Adding upstream version 5:7.2.4.upstream/5%7.2.4

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2666 insertions, 0 deletions

diff --git a/src/ziplist.c b/src/ziplist.c
new file mode 100644
index 0000000..c891625
--- /dev/null
+++ b/src/ziplist.c
@@ -0,0 +1,2666 @@
+/* The ziplist is a specially encoded dually linked list that is designed
+ * to be very memory efficient. It stores both strings and integer values,
+ * where integers are encoded as actual integers instead of a series of
+ * characters. It allows push and pop operations on either side of the list
+ * in O(1) time. However, because every operation requires a reallocation of
+ * the memory used by the ziplist, the actual complexity is related to the
+ * amount of memory used by the ziplist.
+ *
+ * ----------------------------------------------------------------------------
+ *
+ * ZIPLIST OVERALL LAYOUT
+ * ======================
+ *
+ * The general layout of the ziplist is as follows:
+ *
+ * <zlbytes> <zltail> <zllen> <entry> <entry> ... <entry> <zlend>
+ *
+ * NOTE: all fields are stored in little endian, if not specified otherwise.
+ *
+ * <uint32_t zlbytes> is an unsigned integer to hold the number of bytes that
+ * the ziplist occupies, including the four bytes of the zlbytes field itself.
+ * This value needs to be stored to be able to resize the entire structure
+ * without the need to traverse it first.
+ *
+ * <uint32_t zltail> is the offset to the last entry in the list. This allows
+ * a pop operation on the far side of the list without the need for full
+ * traversal.
+ *
+ * <uint16_t zllen> is the number of entries. When there are more than
+ * 2^16-2 entries, this value is set to 2^16-1 and we need to traverse the
+ * entire list to know how many items it holds.
+ *
+ * <uint8_t zlend> is a special entry representing the end of the ziplist.
+ * Is encoded as a single byte equal to 255. No other normal entry starts
+ * with a byte set to the value of 255.
+ *
+ * ZIPLIST ENTRIES
+ * ===============
+ *
+ * Every entry in the ziplist is prefixed by metadata that contains two pieces
+ * of information. First, the length of the previous entry is stored to be
+ * able to traverse the list from back to front. Second, the entry encoding is
+ * provided. It represents the entry type, integer or string, and in the case
+ * of strings it also represents the length of the string payload.
+ * So a complete entry is stored like this:
+ *
+ * <prevlen> <encoding> <entry-data>
+ *
+ * Sometimes the encoding represents the entry itself, like for small integers
+ * as we'll see later. In such a case the <entry-data> part is missing, and we
+ * could have just:
+ *
+ * <prevlen> <encoding>
+ *
+ * The length of the previous entry, <prevlen>, is encoded in the following way:
+ * If this length is smaller than 254 bytes, it will only consume a single
+ * byte representing the length as an unsigned 8 bit integer. When the length
+ * is greater than or equal to 254, it will consume 5 bytes. The first byte is
+ * set to 254 (FE) to indicate a larger value is following. The remaining 4
+ * bytes take the length of the previous entry as value.
+ *
+ * So practically an entry is encoded in the following way:
+ *
+ * <prevlen from 0 to 253> <encoding> <entry>
+ *
+ * Or alternatively if the previous entry length is greater than 253 bytes
+ * the following encoding is used:
+ *
+ * 0xFE <4 bytes unsigned little endian prevlen> <encoding> <entry>
+ *
+ * The encoding field of the entry depends on the content of the
+ * entry. When the entry is a string, the first 2 bits of the encoding first
+ * byte will hold the type of encoding used to store the length of the string,
+ * followed by the actual length of the string. When the entry is an integer
+ * the first 2 bits are both set to 1. The following 2 bits are used to specify
+ * what kind of integer will be stored after this header. An overview of the
+ * different types and encodings is as follows. The first byte is always enough
+ * to determine the kind of entry.
+ *
+ * |00pppppp| - 1 byte
+ *      String value with length less than or equal to 63 bytes (6 bits).
+ *      "pppppp" represents the unsigned 6 bit length.
+ * |01pppppp|qqqqqqqq| - 2 bytes
+ *      String value with length less than or equal to 16383 bytes (14 bits).
+ *      IMPORTANT: The 14 bit number is stored in big endian.
+ * |10000000|qqqqqqqq|rrrrrrrr|ssssssss|tttttttt| - 5 bytes
+ *      String value with length greater than or equal to 16384 bytes.
+ *      Only the 4 bytes following the first byte represents the length
+ *      up to 2^32-1. The 6 lower bits of the first byte are not used and
+ *      are set to zero.
+ *      IMPORTANT: The 32 bit number is stored in big endian.
+ * |11000000| - 3 bytes
+ *      Integer encoded as int16_t (2 bytes).
+ * |11010000| - 5 bytes
+ *      Integer encoded as int32_t (4 bytes).
+ * |11100000| - 9 bytes
+ *      Integer encoded as int64_t (8 bytes).
+ * |11110000| - 4 bytes
+ *      Integer encoded as 24 bit signed (3 bytes).
+ * |11111110| - 2 bytes
+ *      Integer encoded as 8 bit signed (1 byte).
+ * |1111xxxx| - (with xxxx between 0001 and 1101) immediate 4 bit integer.
+ *      Unsigned integer from 0 to 12. The encoded value is actually from
+ *      1 to 13 because 0000 and 1111 can not be used, so 1 should be
+ *      subtracted from the encoded 4 bit value to obtain the right value.
+ * |11111111| - End of ziplist special entry.
+ *
+ * Like for the ziplist header, all the integers are represented in little
+ * endian byte order, even when this code is compiled in big endian systems.
+ *
+ * EXAMPLES OF ACTUAL ZIPLISTS
+ * ===========================
+ *
+ * The following is a ziplist containing the two elements representing
+ * the strings "2" and "5". It is composed of 15 bytes, that we visually
+ * split into sections:
+ *
+ *  [0f 00 00 00] [0c 00 00 00] [02 00] [00 f3] [02 f6] [ff]
+ *        |             |          |       |       |     |
+ *     zlbytes        zltail     zllen    "2"     "5"   end
+ *
+ * The first 4 bytes represent the number 15, that is the number of bytes
+ * the whole ziplist is composed of. The second 4 bytes are the offset
+ * at which the last ziplist entry is found, that is 12, in fact the
+ * last entry, that is "5", is at offset 12 inside the ziplist.
+ * The next 16 bit integer represents the number of elements inside the
+ * ziplist, its value is 2 since there are just two elements inside.
+ * Finally "00 f3" is the first entry representing the number 2. It is
+ * composed of the previous entry length, which is zero because this is
+ * our first entry, and the byte F3 which corresponds to the encoding
+ * |1111xxxx| with xxxx between 0001 and 1101. We need to remove the "F"
+ * higher order bits 1111, and subtract 1 from the "3", so the entry value
+ * is "2". The next entry has a prevlen of 02, since the first entry is
+ * composed of exactly two bytes. The entry itself, F6, is encoded exactly
+ * like the first entry, and 6-1 = 5, so the value of the entry is 5.
+ * Finally the special entry FF signals the end of the ziplist.
+ *
+ * Adding another element to the above string with the value "Hello World"
+ * allows us to show how the ziplist encodes small strings. We'll just show
+ * the hex dump of the entry itself. Imagine the bytes as following the
+ * entry that stores "5" in the ziplist above:
+ *
+ * [02] [0b] [48 65 6c 6c 6f 20 57 6f 72 6c 64]
+ *
+ * The first byte, 02, is the length of the previous entry. The next
+ * byte represents the encoding in the pattern |00pppppp| that means
+ * that the entry is a string of length <pppppp>, so 0B means that
+ * an 11 bytes string follows. From the third byte (48) to the last (64)
+ * there are just the ASCII characters for "Hello World".
+ *
+ * ----------------------------------------------------------------------------
+ *
+ * Copyright (c) 2009-2012, Pieter Noordhuis <pcnoordhuis at gmail dot com>
+ * Copyright (c) 2009-2017, Salvatore Sanfilippo <antirez at gmail dot com>
+ * Copyright (c) 2020, Redis Labs, Inc
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *   * Redistributions of source code must retain the above copyright notice,
+ *     this list of conditions and the following disclaimer.
+ *   * Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *   * Neither the name of Redis nor the names of its contributors may be used
+ *     to endorse or promote products derived from this software without
+ *     specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <limits.h>
+#include "zmalloc.h"
+#include "util.h"
+#include "ziplist.h"
+#include "config.h"
+#include "endianconv.h"
+#include "redisassert.h"
+
+#define ZIP_END 255         /* Special "end of ziplist" entry. */
+#define ZIP_BIG_PREVLEN 254 /* ZIP_BIG_PREVLEN - 1 is the max number of bytes of
+                               the previous entry, for the "prevlen" field prefixing
+                               each entry, to be represented with just a single byte.
+                               Otherwise it is represented as FE AA BB CC DD, where
+                               AA BB CC DD are a 4 bytes unsigned integer
+                               representing the previous entry len. */
+
+/* Different encoding/length possibilities */
+#define ZIP_STR_MASK 0xc0
+#define ZIP_INT_MASK 0x30
+#define ZIP_STR_06B (0 << 6)
+#define ZIP_STR_14B (1 << 6)
+#define ZIP_STR_32B (2 << 6)
+#define ZIP_INT_16B (0xc0 | 0<<4)
+#define ZIP_INT_32B (0xc0 | 1<<4)
+#define ZIP_INT_64B (0xc0 | 2<<4)
+#define ZIP_INT_24B (0xc0 | 3<<4)
+#define ZIP_INT_8B 0xfe
+
+/* 4 bit integer immediate encoding |1111xxxx| with xxxx between
+ * 0001 and 1101. */
+#define ZIP_INT_IMM_MASK 0x0f   /* Mask to extract the 4 bits value. To add
+                                   one is needed to reconstruct the value. */
+#define ZIP_INT_IMM_MIN 0xf1    /* 11110001 */
+#define ZIP_INT_IMM_MAX 0xfd    /* 11111101 */
+
+#define INT24_MAX 0x7fffff
+#define INT24_MIN (-INT24_MAX - 1)
+
+/* Macro to determine if the entry is a string. String entries never start
+ * with "11" as most significant bits of the first byte. */
+#define ZIP_IS_STR(enc) (((enc) & ZIP_STR_MASK) < ZIP_STR_MASK)
+
+/* Utility macros.*/
+
+/* Return total bytes a ziplist is composed of. */
+#define ZIPLIST_BYTES(zl)       (*((uint32_t*)(zl)))
+
+/* Return the offset of the last item inside the ziplist. */
+#define ZIPLIST_TAIL_OFFSET(zl) (*((uint32_t*)((zl)+sizeof(uint32_t))))
+
+/* Return the length of a ziplist, or UINT16_MAX if the length cannot be
+ * determined without scanning the whole ziplist. */
+#define ZIPLIST_LENGTH(zl)      (*((uint16_t*)((zl)+sizeof(uint32_t)*2)))
+
+/* The size of a ziplist header: two 32 bit integers for the total
+ * bytes count and last item offset. One 16 bit integer for the number
+ * of items field. */
+#define ZIPLIST_HEADER_SIZE     (sizeof(uint32_t)*2+sizeof(uint16_t))
+
+/* Size of the "end of ziplist" entry. Just one byte. */
+#define ZIPLIST_END_SIZE        (sizeof(uint8_t))
+
+/* Return the pointer to the first entry of a ziplist. */
+#define ZIPLIST_ENTRY_HEAD(zl)  ((zl)+ZIPLIST_HEADER_SIZE)
+
+/* Return the pointer to the last entry of a ziplist, using the
+ * last entry offset inside the ziplist header. */
+#define ZIPLIST_ENTRY_TAIL(zl)  ((zl)+intrev32ifbe(ZIPLIST_TAIL_OFFSET(zl)))
+
+/* Return the pointer to the last byte of a ziplist, which is, the
+ * end of ziplist FF entry. */
+#define ZIPLIST_ENTRY_END(zl)   ((zl)+intrev32ifbe(ZIPLIST_BYTES(zl))-ZIPLIST_END_SIZE)
+
+/* Increment the number of items field in the ziplist header. Note that this
+ * macro should never overflow the unsigned 16 bit integer, since entries are
+ * always pushed one at a time. When UINT16_MAX is reached we want the count
+ * to stay there to signal that a full scan is needed to get the number of
+ * items inside the ziplist. */
+#define ZIPLIST_INCR_LENGTH(zl,incr) { \
+    if (intrev16ifbe(ZIPLIST_LENGTH(zl)) < UINT16_MAX) \
+        ZIPLIST_LENGTH(zl) = intrev16ifbe(intrev16ifbe(ZIPLIST_LENGTH(zl))+incr); \
+}
+
+/* Don't let ziplists grow over 1GB in any case, don't wanna risk overflow in
+ * zlbytes */
+#define ZIPLIST_MAX_SAFETY_SIZE (1<<30)
+int ziplistSafeToAdd(unsigned char* zl, size_t add) {
+    size_t len = zl? ziplistBlobLen(zl): 0;
+    if (len + add > ZIPLIST_MAX_SAFETY_SIZE)
+        return 0;
+    return 1;
+}
+
+
+/* We use this function to receive information about a ziplist entry.
+ * Note that this is not how the data is actually encoded, is just what we
+ * get filled by a function in order to operate more easily. */
+typedef struct zlentry {
+    unsigned int prevrawlensize; /* Bytes used to encode the previous entry len*/
+    unsigned int prevrawlen;     /* Previous entry len. */
+    unsigned int lensize;        /* Bytes used to encode this entry type/len.
+                                    For example strings have a 1, 2 or 5 bytes
+                                    header. Integers always use a single byte.*/
+    unsigned int len;            /* Bytes used to represent the actual entry.
+                                    For strings this is just the string length
+                                    while for integers it is 1, 2, 3, 4, 8 or
+                                    0 (for 4 bit immediate) depending on the
+                                    number range. */
+    unsigned int headersize;     /* prevrawlensize + lensize. */
+    unsigned char encoding;      /* Set to ZIP_STR_* or ZIP_INT_* depending on
+                                    the entry encoding. However for 4 bits
+                                    immediate integers this can assume a range
+                                    of values and must be range-checked. */
+    unsigned char *p;            /* Pointer to the very start of the entry, that
+                                    is, this points to prev-entry-len field. */
+} zlentry;
+
+#define ZIPLIST_ENTRY_ZERO(zle) { \
+    (zle)->prevrawlensize = (zle)->prevrawlen = 0; \
+    (zle)->lensize = (zle)->len = (zle)->headersize = 0; \
+    (zle)->encoding = 0; \
+    (zle)->p = NULL; \
+}
+
+/* Extract the encoding from the byte pointed by 'ptr' and set it into
+ * 'encoding' field of the zlentry structure. */
+#define ZIP_ENTRY_ENCODING(ptr, encoding) do {  \
+    (encoding) = ((ptr)[0]); \
+    if ((encoding) < ZIP_STR_MASK) (encoding) &= ZIP_STR_MASK; \
+} while(0)
+
+#define ZIP_ENCODING_SIZE_INVALID 0xff
+/* Return the number of bytes required to encode the entry type + length.
+ * On error, return ZIP_ENCODING_SIZE_INVALID */
+static inline unsigned int zipEncodingLenSize(unsigned char encoding) {
+    if (encoding == ZIP_INT_16B || encoding == ZIP_INT_32B ||
+        encoding == ZIP_INT_24B || encoding == ZIP_INT_64B ||
+        encoding == ZIP_INT_8B)
+        return 1;
+    if (encoding >= ZIP_INT_IMM_MIN && encoding <= ZIP_INT_IMM_MAX)
+        return 1;
+    if (encoding == ZIP_STR_06B)
+        return 1;
+    if (encoding == ZIP_STR_14B)
+        return 2;
+    if (encoding == ZIP_STR_32B)
+        return 5;
+    return ZIP_ENCODING_SIZE_INVALID;
+}
+
+#define ZIP_ASSERT_ENCODING(encoding) do {                                     \
+    assert(zipEncodingLenSize(encoding) != ZIP_ENCODING_SIZE_INVALID);         \
+} while (0)
+
+/* Return bytes needed to store integer encoded by 'encoding' */
+static inline unsigned int zipIntSize(unsigned char encoding) {
+    switch(encoding) {
+    case ZIP_INT_8B:  return 1;
+    case ZIP_INT_16B: return 2;
+    case ZIP_INT_24B: return 3;
+    case ZIP_INT_32B: return 4;
+    case ZIP_INT_64B: return 8;
+    }
+    if (encoding >= ZIP_INT_IMM_MIN && encoding <= ZIP_INT_IMM_MAX)
+        return 0; /* 4 bit immediate */
+    /* bad encoding, covered by a previous call to ZIP_ASSERT_ENCODING */
+    redis_unreachable();
+    return 0;
+}
+
+/* Write the encoding header of the entry in 'p'. If p is NULL it just returns
+ * the amount of bytes required to encode such a length. Arguments:
+ *
+ * 'encoding' is the encoding we are using for the entry. It could be
+ * ZIP_INT_* or ZIP_STR_* or between ZIP_INT_IMM_MIN and ZIP_INT_IMM_MAX
+ * for single-byte small immediate integers.
+ *
+ * 'rawlen' is only used for ZIP_STR_* encodings and is the length of the
+ * string that this entry represents.
+ *
+ * The function returns the number of bytes used by the encoding/length
+ * header stored in 'p'. */
+unsigned int zipStoreEntryEncoding(unsigned char *p, unsigned char encoding, unsigned int rawlen) {
+    unsigned char len = 1, buf[5];
+
+    if (ZIP_IS_STR(encoding)) {
+        /* Although encoding is given it may not be set for strings,
+         * so we determine it here using the raw length. */
+        if (rawlen <= 0x3f) {
+            if (!p) return len;
+            buf[0] = ZIP_STR_06B | rawlen;
+        } else if (rawlen <= 0x3fff) {
+            len += 1;
+            if (!p) return len;
+            buf[0] = ZIP_STR_14B | ((rawlen >> 8) & 0x3f);
+            buf[1] = rawlen & 0xff;
+        } else {
+            len += 4;
+            if (!p) return len;
+            buf[0] = ZIP_STR_32B;
+            buf[1] = (rawlen >> 24) & 0xff;
+            buf[2] = (rawlen >> 16) & 0xff;
+            buf[3] = (rawlen >> 8) & 0xff;
+            buf[4] = rawlen & 0xff;
+        }
+    } else {
+        /* Implies integer encoding, so length is always 1. */
+        if (!p) return len;
+        buf[0] = encoding;
+    }
+
+    /* Store this length at p. */
+    memcpy(p,buf,len);
+    return len;
+}
+
+/* Decode the entry encoding type and data length (string length for strings,
+ * number of bytes used for the integer for integer entries) encoded in 'ptr'.
+ * The 'encoding' variable is input, extracted by the caller, the 'lensize'
+ * variable will hold the number of bytes required to encode the entry
+ * length, and the 'len' variable will hold the entry length.
+ * On invalid encoding error, lensize is set to 0. */
+#define ZIP_DECODE_LENGTH(ptr, encoding, lensize, len) do {                    \
+    if ((encoding) < ZIP_STR_MASK) {                                           \
+        if ((encoding) == ZIP_STR_06B) {                                       \
+            (lensize) = 1;                                                     \
+            (len) = (ptr)[0] & 0x3f;                                           \
+        } else if ((encoding) == ZIP_STR_14B) {                                \
+            (lensize) = 2;                                                     \
+            (len) = (((ptr)[0] & 0x3f) << 8) | (ptr)[1];                       \
+        } else if ((encoding) == ZIP_STR_32B) {                                \
+            (lensize) = 5;                                                     \
+            (len) = ((uint32_t)(ptr)[1] << 24) |                               \
+                    ((uint32_t)(ptr)[2] << 16) |                               \
+                    ((uint32_t)(ptr)[3] <<  8) |                               \
+                    ((uint32_t)(ptr)[4]);                                      \
+        } else {                                                               \
+            (lensize) = 0; /* bad encoding, should be covered by a previous */ \
+            (len) = 0;     /* ZIP_ASSERT_ENCODING / zipEncodingLenSize, or  */ \
+                           /* match the lensize after this macro with 0.    */ \
+        }                                                                      \
+    } else {                                                                   \
+        (lensize) = 1;                                                         \
+        if ((encoding) == ZIP_INT_8B)  (len) = 1;                              \
+        else if ((encoding) == ZIP_INT_16B) (len) = 2;                         \
+        else if ((encoding) == ZIP_INT_24B) (len) = 3;                         \
+        else if ((encoding) == ZIP_INT_32B) (len) = 4;                         \
+        else if ((encoding) == ZIP_INT_64B) (len) = 8;                         \
+        else if (encoding >= ZIP_INT_IMM_MIN && encoding <= ZIP_INT_IMM_MAX)   \
+            (len) = 0; /* 4 bit immediate */                                   \
+        else                                                                   \
+            (lensize) = (len) = 0; /* bad encoding */                          \
+    }                                                                          \
+} while(0)
+
+/* Encode the length of the previous entry and write it to "p". This only
+ * uses the larger encoding (required in __ziplistCascadeUpdate). */
+int zipStorePrevEntryLengthLarge(unsigned char *p, unsigned int len) {
+    uint32_t u32;
+    if (p != NULL) {
+        p[0] = ZIP_BIG_PREVLEN;
+        u32 = len;
+        memcpy(p+1,&u32,sizeof(u32));
+        memrev32ifbe(p+1);
+    }
+    return 1 + sizeof(uint32_t);
+}
+
+/* Encode the length of the previous entry and write it to "p". Return the
+ * number of bytes needed to encode this length if "p" is NULL. */
+unsigned int zipStorePrevEntryLength(unsigned char *p, unsigned int len) {
+    if (p == NULL) {
+        return (len < ZIP_BIG_PREVLEN) ? 1 : sizeof(uint32_t) + 1;
+    } else {
+        if (len < ZIP_BIG_PREVLEN) {
+            p[0] = len;
+            return 1;
+        } else {
+            return zipStorePrevEntryLengthLarge(p,len);
+        }
+    }
+}
+
+/* Return the number of bytes used to encode the length of the previous
+ * entry. The length is returned by setting the var 'prevlensize'. */
+#define ZIP_DECODE_PREVLENSIZE(ptr, prevlensize) do {                          \
+    if ((ptr)[0] < ZIP_BIG_PREVLEN) {                                          \
+        (prevlensize) = 1;                                                     \
+    } else {                                                                   \
+        (prevlensize) = 5;                                                     \
+    }                                                                          \
+} while(0)
+
+/* Return the length of the previous element, and the number of bytes that
+ * are used in order to encode the previous element length.
+ * 'ptr' must point to the prevlen prefix of an entry (that encodes the
+ * length of the previous entry in order to navigate the elements backward).
+ * The length of the previous entry is stored in 'prevlen', the number of
+ * bytes needed to encode the previous entry length are stored in
+ * 'prevlensize'. */
+#define ZIP_DECODE_PREVLEN(ptr, prevlensize, prevlen) do {                     \
+    ZIP_DECODE_PREVLENSIZE(ptr, prevlensize);                                  \
+    if ((prevlensize) == 1) {                                                  \
+        (prevlen) = (ptr)[0];                                                  \
+    } else { /* prevlensize == 5 */                                            \
+        (prevlen) = ((ptr)[4] << 24) |                                         \
+                    ((ptr)[3] << 16) |                                         \
+                    ((ptr)[2] <<  8) |                                         \
+                    ((ptr)[1]);                                                \
+    }                                                                          \
+} while(0)
+
+/* Given a pointer 'p' to the prevlen info that prefixes an entry, this
+ * function returns the difference in number of bytes needed to encode
+ * the prevlen if the previous entry changes of size.
+ *
+ * So if A is the number of bytes used right now to encode the 'prevlen'
+ * field.
+ *
+ * And B is the number of bytes that are needed in order to encode the
+ * 'prevlen' if the previous element will be updated to one of size 'len'.
+ *
+ * Then the function returns B - A
+ *
+ * So the function returns a positive number if more space is needed,
+ * a negative number if less space is needed, or zero if the same space
+ * is needed. */
+int zipPrevLenByteDiff(unsigned char *p, unsigned int len) {
+    unsigned int prevlensize;
+    ZIP_DECODE_PREVLENSIZE(p, prevlensize);
+    return zipStorePrevEntryLength(NULL, len) - prevlensize;
+}
+
+/* Check if string pointed to by 'entry' can be encoded as an integer.
+ * Stores the integer value in 'v' and its encoding in 'encoding'. */
+int zipTryEncoding(unsigned char *entry, unsigned int entrylen, long long *v, unsigned char *encoding) {
+    long long value;
+
+    if (entrylen >= 32 || entrylen == 0) return 0;
+    if (string2ll((char*)entry,entrylen,&value)) {
+        /* Great, the string can be encoded. Check what's the smallest
+         * of our encoding types that can hold this value. */
+        if (value >= 0 && value <= 12) {
+            *encoding = ZIP_INT_IMM_MIN+value;
+        } else if (value >= INT8_MIN && value <= INT8_MAX) {
+            *encoding = ZIP_INT_8B;
+        } else if (value >= INT16_MIN && value <= INT16_MAX) {
+            *encoding = ZIP_INT_16B;
+        } else if (value >= INT24_MIN && value <= INT24_MAX) {
+            *encoding = ZIP_INT_24B;
+        } else if (value >= INT32_MIN && value <= INT32_MAX) {
+            *encoding = ZIP_INT_32B;
+        } else {
+            *encoding = ZIP_INT_64B;
+        }
+        *v = value;
+        return 1;
+    }
+    return 0;
+}
+
+/* Store integer 'value' at 'p', encoded as 'encoding' */
+void zipSaveInteger(unsigned char *p, int64_t value, unsigned char encoding) {
+    int16_t i16;
+    int32_t i32;
+    int64_t i64;
+    if (encoding == ZIP_INT_8B) {
+        ((int8_t*)p)[0] = (int8_t)value;
+    } else if (encoding == ZIP_INT_16B) {
+        i16 = value;
+        memcpy(p,&i16,sizeof(i16));
+        memrev16ifbe(p);
+    } else if (encoding == ZIP_INT_24B) {
+        i32 = ((uint64_t)value)<<8;
+        memrev32ifbe(&i32);
+        memcpy(p,((uint8_t*)&i32)+1,sizeof(i32)-sizeof(uint8_t));
+    } else if (encoding == ZIP_INT_32B) {
+        i32 = value;
+        memcpy(p,&i32,sizeof(i32));
+        memrev32ifbe(p);
+    } else if (encoding == ZIP_INT_64B) {
+        i64 = value;
+        memcpy(p,&i64,sizeof(i64));
+        memrev64ifbe(p);
+    } else if (encoding >= ZIP_INT_IMM_MIN && encoding <= ZIP_INT_IMM_MAX) {
+        /* Nothing to do, the value is stored in the encoding itself. */
+    } else {
+        assert(NULL);
+    }
+}
+
+/* Read integer encoded as 'encoding' from 'p' */
+int64_t zipLoadInteger(unsigned char *p, unsigned char encoding) {
+    int16_t i16;
+    int32_t i32;
+    int64_t i64, ret = 0;
+    if (encoding == ZIP_INT_8B) {
+        ret = ((int8_t*)p)[0];
+    } else if (encoding == ZIP_INT_16B) {
+        memcpy(&i16,p,sizeof(i16));
+        memrev16ifbe(&i16);
+        ret = i16;
+    } else if (encoding == ZIP_INT_32B) {
+        memcpy(&i32,p,sizeof(i32));
+        memrev32ifbe(&i32);
+        ret = i32;
+    } else if (encoding == ZIP_INT_24B) {
+        i32 = 0;
+        memcpy(((uint8_t*)&i32)+1,p,sizeof(i32)-sizeof(uint8_t));
+        memrev32ifbe(&i32);
+        ret = i32>>8;
+    } else if (encoding == ZIP_INT_64B) {
+        memcpy(&i64,p,sizeof(i64));
+        memrev64ifbe(&i64);
+        ret = i64;
+    } else if (encoding >= ZIP_INT_IMM_MIN && encoding <= ZIP_INT_IMM_MAX) {
+        ret = (encoding & ZIP_INT_IMM_MASK)-1;
+    } else {
+        assert(NULL);
+    }
+    return ret;
+}
+
+/* Fills a struct with all information about an entry.
+ * This function is the "unsafe" alternative to the one below.
+ * Generally, all function that return a pointer to an element in the ziplist
+ * will assert that this element is valid, so it can be freely used.
+ * Generally functions such ziplistGet assume the input pointer is already
+ * validated (since it's the return value of another function). */
+static inline void zipEntry(unsigned char *p, zlentry *e) {
+    ZIP_DECODE_PREVLEN(p, e->prevrawlensize, e->prevrawlen);
+    ZIP_ENTRY_ENCODING(p + e->prevrawlensize, e->encoding);
+    ZIP_DECODE_LENGTH(p + e->prevrawlensize, e->encoding, e->lensize, e->len);
+    assert(e->lensize != 0); /* check that encoding was valid. */
+    e->headersize = e->prevrawlensize + e->lensize;
+    e->p = p;
+}
+
+/* Fills a struct with all information about an entry.
+ * This function is safe to use on untrusted pointers, it'll make sure not to
+ * try to access memory outside the ziplist payload.
+ * Returns 1 if the entry is valid, and 0 otherwise. */
+static inline int zipEntrySafe(unsigned char* zl, size_t zlbytes, unsigned char *p, zlentry *e, int validate_prevlen) {
+    unsigned char *zlfirst = zl + ZIPLIST_HEADER_SIZE;
+    unsigned char *zllast = zl + zlbytes - ZIPLIST_END_SIZE;
+#define OUT_OF_RANGE(p) (unlikely((p) < zlfirst || (p) > zllast))
+
+    /* If there's no possibility for the header to reach outside the ziplist,
+     * take the fast path. (max lensize and prevrawlensize are both 5 bytes) */
+    if (p >= zlfirst && p + 10 < zllast) {
+        ZIP_DECODE_PREVLEN(p, e->prevrawlensize, e->prevrawlen);
+        ZIP_ENTRY_ENCODING(p + e->prevrawlensize, e->encoding);
+        ZIP_DECODE_LENGTH(p + e->prevrawlensize, e->encoding, e->lensize, e->len);
+        e->headersize = e->prevrawlensize + e->lensize;
+        e->p = p;
+        /* We didn't call ZIP_ASSERT_ENCODING, so we check lensize was set to 0. */
+        if (unlikely(e->lensize == 0))
+            return 0;
+        /* Make sure the entry doesn't reach outside the edge of the ziplist */
+        if (OUT_OF_RANGE(p + e->headersize + e->len))
+            return 0;
+        /* Make sure prevlen doesn't reach outside the edge of the ziplist */
+        if (validate_prevlen && OUT_OF_RANGE(p - e->prevrawlen))
+            return 0;
+        return 1;
+    }
+
+    /* Make sure the pointer doesn't reach outside the edge of the ziplist */
+    if (OUT_OF_RANGE(p))
+        return 0;
+
+    /* Make sure the encoded prevlen header doesn't reach outside the allocation */
+    ZIP_DECODE_PREVLENSIZE(p, e->prevrawlensize);
+    if (OUT_OF_RANGE(p + e->prevrawlensize))
+        return 0;
+
+    /* Make sure encoded entry header is valid. */
+    ZIP_ENTRY_ENCODING(p + e->prevrawlensize, e->encoding);
+    e->lensize = zipEncodingLenSize(e->encoding);
+    if (unlikely(e->lensize == ZIP_ENCODING_SIZE_INVALID))
+        return 0;
+
+    /* Make sure the encoded entry header doesn't reach outside the allocation */
+    if (OUT_OF_RANGE(p + e->prevrawlensize + e->lensize))
+        return 0;
+
+    /* Decode the prevlen and entry len headers. */
+    ZIP_DECODE_PREVLEN(p, e->prevrawlensize, e->prevrawlen);
+    ZIP_DECODE_LENGTH(p + e->prevrawlensize, e->encoding, e->lensize, e->len);
+    e->headersize = e->prevrawlensize + e->lensize;
+
+    /* Make sure the entry doesn't reach outside the edge of the ziplist */
+    if (OUT_OF_RANGE(p + e->headersize + e->len))
+        return 0;
+
+    /* Make sure prevlen doesn't reach outside the edge of the ziplist */
+    if (validate_prevlen && OUT_OF_RANGE(p - e->prevrawlen))
+        return 0;
+
+    e->p = p;
+    return 1;
+#undef OUT_OF_RANGE
+}
+
+/* Return the total number of bytes used by the entry pointed to by 'p'. */
+static inline unsigned int zipRawEntryLengthSafe(unsigned char* zl, size_t zlbytes, unsigned char *p) {
+    zlentry e;
+    assert(zipEntrySafe(zl, zlbytes, p, &e, 0));
+    return e.headersize + e.len;
+}
+
+/* Return the total number of bytes used by the entry pointed to by 'p'. */
+static inline unsigned int zipRawEntryLength(unsigned char *p) {
+    zlentry e;
+    zipEntry(p, &e);
+    return e.headersize + e.len;
+}
+
+/* Validate that the entry doesn't reach outside the ziplist allocation. */
+static inline void zipAssertValidEntry(unsigned char* zl, size_t zlbytes, unsigned char *p) {
+    zlentry e;
+    assert(zipEntrySafe(zl, zlbytes, p, &e, 1));
+}
+
+/* Create a new empty ziplist. */
+unsigned char *ziplistNew(void) {
+    unsigned int bytes = ZIPLIST_HEADER_SIZE+ZIPLIST_END_SIZE;
+    unsigned char *zl = zmalloc(bytes);
+    ZIPLIST_BYTES(zl) = intrev32ifbe(bytes);
+    ZIPLIST_TAIL_OFFSET(zl) = intrev32ifbe(ZIPLIST_HEADER_SIZE);
+    ZIPLIST_LENGTH(zl) = 0;
+    zl[bytes-1] = ZIP_END;
+    return zl;
+}
+
+/* Resize the ziplist. */
+unsigned char *ziplistResize(unsigned char *zl, size_t len) {
+    assert(len < UINT32_MAX);
+    zl = zrealloc(zl,len);
+    ZIPLIST_BYTES(zl) = intrev32ifbe(len);
+    zl[len-1] = ZIP_END;
+    return zl;
+}
+
+/* When an entry is inserted, we need to set the prevlen field of the next
+ * entry to equal the length of the inserted entry. It can occur that this
+ * length cannot be encoded in 1 byte and the next entry needs to be grow
+ * a bit larger to hold the 5-byte encoded prevlen. This can be done for free,
+ * because this only happens when an entry is already being inserted (which
+ * causes a realloc and memmove). However, encoding the prevlen may require
+ * that this entry is grown as well. This effect may cascade throughout
+ * the ziplist when there are consecutive entries with a size close to
+ * ZIP_BIG_PREVLEN, so we need to check that the prevlen can be encoded in
+ * every consecutive entry.
+ *
+ * Note that this effect can also happen in reverse, where the bytes required
+ * to encode the prevlen field can shrink. This effect is deliberately ignored,
+ * because it can cause a "flapping" effect where a chain prevlen fields is
+ * first grown and then shrunk again after consecutive inserts. Rather, the
+ * field is allowed to stay larger than necessary, because a large prevlen
+ * field implies the ziplist is holding large entries anyway.
+ *
+ * The pointer "p" points to the first entry that does NOT need to be
+ * updated, i.e. consecutive fields MAY need an update. */
+unsigned char *__ziplistCascadeUpdate(unsigned char *zl, unsigned char *p) {
+    zlentry cur;
+    size_t prevlen, prevlensize, prevoffset; /* Informat of the last changed entry. */
+    size_t firstentrylen; /* Used to handle insert at head. */
+    size_t rawlen, curlen = intrev32ifbe(ZIPLIST_BYTES(zl));
+    size_t extra = 0, cnt = 0, offset;
+    size_t delta = 4; /* Extra bytes needed to update a entry's prevlen (5-1). */
+    unsigned char *tail = zl + intrev32ifbe(ZIPLIST_TAIL_OFFSET(zl));
+
+    /* Empty ziplist */
+    if (p[0] == ZIP_END) return zl;
+
+    zipEntry(p, &cur); /* no need for "safe" variant since the input pointer was validated by the function that returned it. */
+    firstentrylen = prevlen = cur.headersize + cur.len;
+    prevlensize = zipStorePrevEntryLength(NULL, prevlen);
+    prevoffset = p - zl;
+    p += prevlen;
+
+    /* Iterate ziplist to find out how many extra bytes do we need to update it. */
+    while (p[0] != ZIP_END) {
+        assert(zipEntrySafe(zl, curlen, p, &cur, 0));
+
+        /* Abort when "prevlen" has not changed. */
+        if (cur.prevrawlen == prevlen) break;
+
+        /* Abort when entry's "prevlensize" is big enough. */
+        if (cur.prevrawlensize >= prevlensize) {
+            if (cur.prevrawlensize == prevlensize) {
+                zipStorePrevEntryLength(p, prevlen);
+            } else {
+                /* This would result in shrinking, which we want to avoid.
+                 * So, set "prevlen" in the available bytes. */
+                zipStorePrevEntryLengthLarge(p, prevlen);
+            }
+            break;
+        }
+
+        /* cur.prevrawlen means cur is the former head entry. */
+        assert(cur.prevrawlen == 0 || cur.prevrawlen + delta == prevlen);
+
+        /* Update prev entry's info and advance the cursor. */
+        rawlen = cur.headersize + cur.len;
+        prevlen = rawlen + delta; 
+        prevlensize = zipStorePrevEntryLength(NULL, prevlen);
+        prevoffset = p - zl;
+        p += rawlen;
+        extra += delta;
+        cnt++;
+    }
+
+    /* Extra bytes is zero all update has been done(or no need to update). */
+    if (extra == 0) return zl;
+
+    /* Update tail offset after loop. */
+    if (tail == zl + prevoffset) {
+        /* When the last entry we need to update is also the tail, update tail offset
+         * unless this is the only entry that was updated (so the tail offset didn't change). */
+        if (extra - delta != 0) {
+            ZIPLIST_TAIL_OFFSET(zl) =
+                intrev32ifbe(intrev32ifbe(ZIPLIST_TAIL_OFFSET(zl))+extra-delta);
+        }
+    } else {
+        /* Update the tail offset in cases where the last entry we updated is not the tail. */
+        ZIPLIST_TAIL_OFFSET(zl) =
+            intrev32ifbe(intrev32ifbe(ZIPLIST_TAIL_OFFSET(zl))+extra);
+    }
+
+    /* Now "p" points at the first unchanged byte in original ziplist,
+     * move data after that to new ziplist. */
+    offset = p - zl;
+    zl = ziplistResize(zl, curlen + extra);
+    p = zl + offset;
+    memmove(p + extra, p, curlen - offset - 1);
+    p += extra;
+
+    /* Iterate all entries that need to be updated tail to head. */
+    while (cnt) {
+        zipEntry(zl + prevoffset, &cur); /* no need for "safe" variant since we already iterated on all these entries above. */
+        rawlen = cur.headersize + cur.len;
+        /* Move entry to tail and reset prevlen. */
+        memmove(p - (rawlen - cur.prevrawlensize), 
+                zl + prevoffset + cur.prevrawlensize, 
+                rawlen - cur.prevrawlensize);
+        p -= (rawlen + delta);
+        if (cur.prevrawlen == 0) {
+            /* "cur" is the previous head entry, update its prevlen with firstentrylen. */
+            zipStorePrevEntryLength(p, firstentrylen);
+        } else {
+            /* An entry's prevlen can only increment 4 bytes. */
+            zipStorePrevEntryLength(p, cur.prevrawlen+delta);
+        }
+        /* Forward to previous entry. */
+        prevoffset -= cur.prevrawlen;
+        cnt--;
+    }
+    return zl;
+}
+
+/* Delete "num" entries, starting at "p". Returns pointer to the ziplist. */
+unsigned char *__ziplistDelete(unsigned char *zl, unsigned char *p, unsigned int num) {
+    unsigned int i, totlen, deleted = 0;
+    size_t offset;
+    int nextdiff = 0;
+    zlentry first, tail;
+    size_t zlbytes = intrev32ifbe(ZIPLIST_BYTES(zl));
+
+    zipEntry(p, &first); /* no need for "safe" variant since the input pointer was validated by the function that returned it. */
+    for (i = 0; p[0] != ZIP_END && i < num; i++) {
+        p += zipRawEntryLengthSafe(zl, zlbytes, p);
+        deleted++;
+    }
+
+    assert(p >= first.p);
+    totlen = p-first.p; /* Bytes taken by the element(s) to delete. */
+    if (totlen > 0) {
+        uint32_t set_tail;
+        if (p[0] != ZIP_END) {
+            /* Storing `prevrawlen` in this entry may increase or decrease the
+             * number of bytes required compare to the current `prevrawlen`.
+             * There always is room to store this, because it was previously
+             * stored by an entry that is now being deleted. */
+            nextdiff = zipPrevLenByteDiff(p,first.prevrawlen);
+
+            /* Note that there is always space when p jumps backward: if
+             * the new previous entry is large, one of the deleted elements
+             * had a 5 bytes prevlen header, so there is for sure at least
+             * 5 bytes free and we need just 4. */
+            p -= nextdiff;
+            assert(p >= first.p && p<zl+zlbytes-1);
+            zipStorePrevEntryLength(p,first.prevrawlen);
+
+            /* Update offset for tail */
+            set_tail = intrev32ifbe(ZIPLIST_TAIL_OFFSET(zl))-totlen;
+
+            /* When the tail contains more than one entry, we need to take
+             * "nextdiff" in account as well. Otherwise, a change in the
+             * size of prevlen doesn't have an effect on the *tail* offset. */
+            assert(zipEntrySafe(zl, zlbytes, p, &tail, 1));
+            if (p[tail.headersize+tail.len] != ZIP_END) {
+                set_tail = set_tail + nextdiff;
+            }
+
+            /* Move tail to the front of the ziplist */
+            /* since we asserted that p >= first.p. we know totlen >= 0,
+             * so we know that p > first.p and this is guaranteed not to reach
+             * beyond the allocation, even if the entries lens are corrupted. */
+            size_t bytes_to_move = zlbytes-(p-zl)-1;
+            memmove(first.p,p,bytes_to_move);
+        } else {
+            /* The entire tail was deleted. No need to move memory. */
+            set_tail = (first.p-zl)-first.prevrawlen;
+        }
+
+        /* Resize the ziplist */
+        offset = first.p-zl;
+        zlbytes -= totlen - nextdiff;
+        zl = ziplistResize(zl, zlbytes);
+        p = zl+offset;
+
+        /* Update record count */
+        ZIPLIST_INCR_LENGTH(zl,-deleted);
+
+        /* Set the tail offset computed above */
+        assert(set_tail <= zlbytes - ZIPLIST_END_SIZE);
+        ZIPLIST_TAIL_OFFSET(zl) = intrev32ifbe(set_tail);
+
+        /* When nextdiff != 0, the raw length of the next entry has changed, so
+         * we need to cascade the update throughout the ziplist */
+        if (nextdiff != 0)
+            zl = __ziplistCascadeUpdate(zl,p);
+    }
+    return zl;
+}
+
+/* Insert item at "p". */
+unsigned char *__ziplistInsert(unsigned char *zl, unsigned char *p, unsigned char *s, unsigned int slen) {
+    size_t curlen = intrev32ifbe(ZIPLIST_BYTES(zl)), reqlen, newlen;
+    unsigned int prevlensize, prevlen = 0;
+    size_t offset;
+    int nextdiff = 0;
+    unsigned char encoding = 0;
+    long long value = 123456789; /* initialized to avoid warning. Using a value
+                                    that is easy to see if for some reason
+                                    we use it uninitialized. */
+    zlentry tail;
+
+    /* Find out prevlen for the entry that is inserted. */
+    if (p[0] != ZIP_END) {
+        ZIP_DECODE_PREVLEN(p, prevlensize, prevlen);
+    } else {
+        unsigned char *ptail = ZIPLIST_ENTRY_TAIL(zl);
+        if (ptail[0] != ZIP_END) {
+            prevlen = zipRawEntryLengthSafe(zl, curlen, ptail);
+        }
+    }
+
+    /* See if the entry can be encoded */
+    if (zipTryEncoding(s,slen,&value,&encoding)) {
+        /* 'encoding' is set to the appropriate integer encoding */
+        reqlen = zipIntSize(encoding);
+    } else {
+        /* 'encoding' is untouched, however zipStoreEntryEncoding will use the
+         * string length to figure out how to encode it. */
+        reqlen = slen;
+    }
+    /* We need space for both the length of the previous entry and
+     * the length of the payload. */
+    reqlen += zipStorePrevEntryLength(NULL,prevlen);
+    reqlen += zipStoreEntryEncoding(NULL,encoding,slen);
+
+    /* When the insert position is not equal to the tail, we need to
+     * make sure that the next entry can hold this entry's length in
+     * its prevlen field. */
+    int forcelarge = 0;
+    nextdiff = (p[0] != ZIP_END) ? zipPrevLenByteDiff(p,reqlen) : 0;
+    if (nextdiff == -4 && reqlen < 4) {
+        nextdiff = 0;
+        forcelarge = 1;
+    }
+
+    /* Store offset because a realloc may change the address of zl. */
+    offset = p-zl;
+    newlen = curlen+reqlen+nextdiff;
+    zl = ziplistResize(zl,newlen);
+    p = zl+offset;
+
+    /* Apply memory move when necessary and update tail offset. */
+    if (p[0] != ZIP_END) {
+        /* Subtract one because of the ZIP_END bytes */
+        memmove(p+reqlen,p-nextdiff,curlen-offset-1+nextdiff);
+
+        /* Encode this entry's raw length in the next entry. */
+        if (forcelarge)
+            zipStorePrevEntryLengthLarge(p+reqlen,reqlen);
+        else
+            zipStorePrevEntryLength(p+reqlen,reqlen);
+
+        /* Update offset for tail */
+        ZIPLIST_TAIL_OFFSET(zl) =
+            intrev32ifbe(intrev32ifbe(ZIPLIST_TAIL_OFFSET(zl))+reqlen);
+
+        /* When the tail contains more than one entry, we need to take
+         * "nextdiff" in account as well. Otherwise, a change in the
+         * size of prevlen doesn't have an effect on the *tail* offset. */
+        assert(zipEntrySafe(zl, newlen, p+reqlen, &tail, 1));
+        if (p[reqlen+tail.headersize+tail.len] != ZIP_END) {
+            ZIPLIST_TAIL_OFFSET(zl) =
+                intrev32ifbe(intrev32ifbe(ZIPLIST_TAIL_OFFSET(zl))+nextdiff);
+        }
+    } else {
+        /* This element will be the new tail. */
+        ZIPLIST_TAIL_OFFSET(zl) = intrev32ifbe(p-zl);
+    }
+
+    /* When nextdiff != 0, the raw length of the next entry has changed, so
+     * we need to cascade the update throughout the ziplist */
+    if (nextdiff != 0) {
+        offset = p-zl;
+        zl = __ziplistCascadeUpdate(zl,p+reqlen);
+        p = zl+offset;
+    }
+
+    /* Write the entry */
+    p += zipStorePrevEntryLength(p,prevlen);
+    p += zipStoreEntryEncoding(p,encoding,slen);
+    if (ZIP_IS_STR(encoding)) {
+        memcpy(p,s,slen);
+    } else {
+        zipSaveInteger(p,value,encoding);
+    }
+    ZIPLIST_INCR_LENGTH(zl,1);
+    return zl;
+}
+
+/* Merge ziplists 'first' and 'second' by appending 'second' to 'first'.
+ *
+ * NOTE: The larger ziplist is reallocated to contain the new merged ziplist.
+ * Either 'first' or 'second' can be used for the result.  The parameter not
+ * used will be free'd and set to NULL.
+ *
+ * After calling this function, the input parameters are no longer valid since
+ * they are changed and free'd in-place.
+ *
+ * The result ziplist is the contents of 'first' followed by 'second'.
+ *
+ * On failure: returns NULL if the merge is impossible.
+ * On success: returns the merged ziplist (which is expanded version of either
+ * 'first' or 'second', also frees the other unused input ziplist, and sets the
+ * input ziplist argument equal to newly reallocated ziplist return value. */
+unsigned char *ziplistMerge(unsigned char **first, unsigned char **second) {
+    /* If any params are null, we can't merge, so NULL. */
+    if (first == NULL || *first == NULL || second == NULL || *second == NULL)
+        return NULL;
+
+    /* Can't merge same list into itself. */
+    if (*first == *second)
+        return NULL;
+
+    size_t first_bytes = intrev32ifbe(ZIPLIST_BYTES(*first));
+    size_t first_len = intrev16ifbe(ZIPLIST_LENGTH(*first));
+
+    size_t second_bytes = intrev32ifbe(ZIPLIST_BYTES(*second));
+    size_t second_len = intrev16ifbe(ZIPLIST_LENGTH(*second));
+
+    int append;
+    unsigned char *source, *target;
+    size_t target_bytes, source_bytes;
+    /* Pick the largest ziplist so we can resize easily in-place.
+     * We must also track if we are now appending or prepending to
+     * the target ziplist. */
+    if (first_len >= second_len) {
+        /* retain first, append second to first. */
+        target = *first;
+        target_bytes = first_bytes;
+        source = *second;
+        source_bytes = second_bytes;
+        append = 1;
+    } else {
+        /* else, retain second, prepend first to second. */
+        target = *second;
+        target_bytes = second_bytes;
+        source = *first;
+        source_bytes = first_bytes;
+        append = 0;
+    }
+
+    /* Calculate final bytes (subtract one pair of metadata) */
+    size_t zlbytes = first_bytes + second_bytes -
+                     ZIPLIST_HEADER_SIZE - ZIPLIST_END_SIZE;
+    size_t zllength = first_len + second_len;
+
+    /* Combined zl length should be limited within UINT16_MAX */
+    zllength = zllength < UINT16_MAX ? zllength : UINT16_MAX;
+
+    /* larger values can't be stored into ZIPLIST_BYTES */
+    assert(zlbytes < UINT32_MAX);
+
+    /* Save offset positions before we start ripping memory apart. */
+    size_t first_offset = intrev32ifbe(ZIPLIST_TAIL_OFFSET(*first));
+    size_t second_offset = intrev32ifbe(ZIPLIST_TAIL_OFFSET(*second));
+
+    /* Extend target to new zlbytes then append or prepend source. */
+    target = zrealloc(target, zlbytes);
+    if (append) {
+        /* append == appending to target */
+        /* Copy source after target (copying over original [END]):
+         *   [TARGET - END, SOURCE - HEADER] */
+        memcpy(target + target_bytes - ZIPLIST_END_SIZE,
+               source + ZIPLIST_HEADER_SIZE,
+               source_bytes - ZIPLIST_HEADER_SIZE);
+    } else {
+        /* !append == prepending to target */
+        /* Move target *contents* exactly size of (source - [END]),
+         * then copy source into vacated space (source - [END]):
+         *   [SOURCE - END, TARGET - HEADER] */
+        memmove(target + source_bytes - ZIPLIST_END_SIZE,
+                target + ZIPLIST_HEADER_SIZE,
+                target_bytes - ZIPLIST_HEADER_SIZE);
+        memcpy(target, source, source_bytes - ZIPLIST_END_SIZE);
+    }
+
+    /* Update header metadata. */
+    ZIPLIST_BYTES(target) = intrev32ifbe(zlbytes);
+    ZIPLIST_LENGTH(target) = intrev16ifbe(zllength);
+    /* New tail offset is:
+     *   + N bytes of first ziplist
+     *   - 1 byte for [END] of first ziplist
+     *   + M bytes for the offset of the original tail of the second ziplist
+     *   - J bytes for HEADER because second_offset keeps no header. */
+    ZIPLIST_TAIL_OFFSET(target) = intrev32ifbe(
+                                   (first_bytes - ZIPLIST_END_SIZE) +
+                                   (second_offset - ZIPLIST_HEADER_SIZE));
+
+    /* __ziplistCascadeUpdate just fixes the prev length values until it finds a
+     * correct prev length value (then it assumes the rest of the list is okay).
+     * We tell CascadeUpdate to start at the first ziplist's tail element to fix
+     * the merge seam. */
+    target = __ziplistCascadeUpdate(target, target+first_offset);
+
+    /* Now free and NULL out what we didn't realloc */
+    if (append) {
+        zfree(*second);
+        *second = NULL;
+        *first = target;
+    } else {
+        zfree(*first);
+        *first = NULL;
+        *second = target;
+    }
+    return target;
+}
+
+unsigned char *ziplistPush(unsigned char *zl, unsigned char *s, unsigned int slen, int where) {
+    unsigned char *p;
+    p = (where == ZIPLIST_HEAD) ? ZIPLIST_ENTRY_HEAD(zl) : ZIPLIST_ENTRY_END(zl);
+    return __ziplistInsert(zl,p,s,slen);
+}
+
+/* Returns an offset to use for iterating with ziplistNext. When the given
+ * index is negative, the list is traversed back to front. When the list
+ * doesn't contain an element at the provided index, NULL is returned. */
+unsigned char *ziplistIndex(unsigned char *zl, int index) {
+    unsigned char *p;
+    unsigned int prevlensize, prevlen = 0;
+    size_t zlbytes = intrev32ifbe(ZIPLIST_BYTES(zl));
+    if (index < 0) {
+        index = (-index)-1;
+        p = ZIPLIST_ENTRY_TAIL(zl);
+        if (p[0] != ZIP_END) {
+            /* No need for "safe" check: when going backwards, we know the header
+             * we're parsing is in the range, we just need to assert (below) that
+             * the size we take doesn't cause p to go outside the allocation. */
+            ZIP_DECODE_PREVLENSIZE(p, prevlensize);
+            assert(p + prevlensize < zl + zlbytes - ZIPLIST_END_SIZE);
+            ZIP_DECODE_PREVLEN(p, prevlensize, prevlen);
+            while (prevlen > 0 && index--) {
+                p -= prevlen;
+                assert(p >= zl + ZIPLIST_HEADER_SIZE && p < zl + zlbytes - ZIPLIST_END_SIZE);
+                ZIP_DECODE_PREVLEN(p, prevlensize, prevlen);
+            }
+        }
+    } else {
+        p = ZIPLIST_ENTRY_HEAD(zl);
+        while (index--) {
+            /* Use the "safe" length: When we go forward, we need to be careful
+             * not to decode an entry header if it's past the ziplist allocation. */
+            p += zipRawEntryLengthSafe(zl, zlbytes, p);
+            if (p[0] == ZIP_END)
+                break;
+        }
+    }
+    if (p[0] == ZIP_END || index > 0)
+        return NULL;
+    zipAssertValidEntry(zl, zlbytes, p);
+    return p;
+}
+
+/* Return pointer to next entry in ziplist.
+ *
+ * zl is the pointer to the ziplist
+ * p is the pointer to the current element
+ *
+ * The element after 'p' is returned, otherwise NULL if we are at the end. */
+unsigned char *ziplistNext(unsigned char *zl, unsigned char *p) {
+    ((void) zl);
+    size_t zlbytes = intrev32ifbe(ZIPLIST_BYTES(zl));
+
+    /* "p" could be equal to ZIP_END, caused by ziplistDelete,
+     * and we should return NULL. Otherwise, we should return NULL
+     * when the *next* element is ZIP_END (there is no next entry). */
+    if (p[0] == ZIP_END) {
+        return NULL;
+    }
+
+    p += zipRawEntryLength(p);
+    if (p[0] == ZIP_END) {
+        return NULL;
+    }
+
+    zipAssertValidEntry(zl, zlbytes, p);
+    return p;
+}
+
+/* Return pointer to previous entry in ziplist. */
+unsigned char *ziplistPrev(unsigned char *zl, unsigned char *p) {
+    unsigned int prevlensize, prevlen = 0;
+
+    /* Iterating backwards from ZIP_END should return the tail. When "p" is
+     * equal to the first element of the list, we're already at the head,
+     * and should return NULL. */
+    if (p[0] == ZIP_END) {
+        p = ZIPLIST_ENTRY_TAIL(zl);
+        return (p[0] == ZIP_END) ? NULL : p;
+    } else if (p == ZIPLIST_ENTRY_HEAD(zl)) {
+        return NULL;
+    } else {
+        ZIP_DECODE_PREVLEN(p, prevlensize, prevlen);
+        assert(prevlen > 0);
+        p-=prevlen;
+        size_t zlbytes = intrev32ifbe(ZIPLIST_BYTES(zl));
+        zipAssertValidEntry(zl, zlbytes, p);
+        return p;
+    }
+}
+
+/* Get entry pointed to by 'p' and store in either '*sstr' or 'sval' depending
+ * on the encoding of the entry. '*sstr' is always set to NULL to be able
+ * to find out whether the string pointer or the integer value was set.
+ * Return 0 if 'p' points to the end of the ziplist, 1 otherwise. */
+unsigned int ziplistGet(unsigned char *p, unsigned char **sstr, unsigned int *slen, long long *sval) {
+    zlentry entry;
+    if (p == NULL || p[0] == ZIP_END) return 0;
+    if (sstr) *sstr = NULL;
+
+    zipEntry(p, &entry); /* no need for "safe" variant since the input pointer was validated by the function that returned it. */
+    if (ZIP_IS_STR(entry.encoding)) {
+        if (sstr) {
+            *slen = entry.len;
+            *sstr = p+entry.headersize;
+        }
+    } else {
+        if (sval) {
+            *sval = zipLoadInteger(p+entry.headersize,entry.encoding);
+        }
+    }
+    return 1;
+}
+
+/* Insert an entry at "p". */
+unsigned char *ziplistInsert(unsigned char *zl, unsigned char *p, unsigned char *s, unsigned int slen) {
+    return __ziplistInsert(zl,p,s,slen);
+}
+
+/* Delete a single entry from the ziplist, pointed to by *p.
+ * Also update *p in place, to be able to iterate over the
+ * ziplist, while deleting entries. */
+unsigned char *ziplistDelete(unsigned char *zl, unsigned char **p) {
+    size_t offset = *p-zl;
+    zl = __ziplistDelete(zl,*p,1);
+
+    /* Store pointer to current element in p, because ziplistDelete will
+     * do a realloc which might result in a different "zl"-pointer.
+     * When the delete direction is back to front, we might delete the last
+     * entry and end up with "p" pointing to ZIP_END, so check this. */
+    *p = zl+offset;
+    return zl;
+}
+
+/* Delete a range of entries from the ziplist. */
+unsigned char *ziplistDeleteRange(unsigned char *zl, int index, unsigned int num) {
+    unsigned char *p = ziplistIndex(zl,index);
+    return (p == NULL) ? zl : __ziplistDelete(zl,p,num);
+}
+
+/* Replaces the entry at p. This is equivalent to a delete and an insert,
+ * but avoids some overhead when replacing a value of the same size. */
+unsigned char *ziplistReplace(unsigned char *zl, unsigned char *p, unsigned char *s, unsigned int slen) {
+
+    /* get metadata of the current entry */
+    zlentry entry;
+    zipEntry(p, &entry);
+
+    /* compute length of entry to store, excluding prevlen */
+    unsigned int reqlen;
+    unsigned char encoding = 0;
+    long long value = 123456789; /* initialized to avoid warning. */
+    if (zipTryEncoding(s,slen,&value,&encoding)) {
+        reqlen = zipIntSize(encoding); /* encoding is set */
+    } else {
+        reqlen = slen; /* encoding == 0 */
+    }
+    reqlen += zipStoreEntryEncoding(NULL,encoding,slen);
+
+    if (reqlen == entry.lensize + entry.len) {
+        /* Simply overwrite the element. */
+        p += entry.prevrawlensize;
+        p += zipStoreEntryEncoding(p,encoding,slen);
+        if (ZIP_IS_STR(encoding)) {
+            memcpy(p,s,slen);
+        } else {
+            zipSaveInteger(p,value,encoding);
+        }
+    } else {
+        /* Fallback. */
+        zl = ziplistDelete(zl,&p);
+        zl = ziplistInsert(zl,p,s,slen);
+    }
+    return zl;
+}
+
+/* Compare entry pointer to by 'p' with 'sstr' of length 'slen'. */
+/* Return 1 if equal. */
+unsigned int ziplistCompare(unsigned char *p, unsigned char *sstr, unsigned int slen) {
+    zlentry entry;
+    unsigned char sencoding;
+    long long zval, sval;
+    if (p[0] == ZIP_END) return 0;
+
+    zipEntry(p, &entry); /* no need for "safe" variant since the input pointer was validated by the function that returned it. */
+    if (ZIP_IS_STR(entry.encoding)) {
+        /* Raw compare */
+        if (entry.len == slen) {
+            return memcmp(p+entry.headersize,sstr,slen) == 0;
+        } else {
+            return 0;
+        }
+    } else {
+        /* Try to compare encoded values. Don't compare encoding because
+         * different implementations may encoded integers differently. */
+        if (zipTryEncoding(sstr,slen,&sval,&sencoding)) {
+          zval = zipLoadInteger(p+entry.headersize,entry.encoding);
+          return zval == sval;
+        }
+    }
+    return 0;
+}
+
+/* Find pointer to the entry equal to the specified entry. Skip 'skip' entries
+ * between every comparison. Returns NULL when the field could not be found. */
+unsigned char *ziplistFind(unsigned char *zl, unsigned char *p, unsigned char *vstr, unsigned int vlen, unsigned int skip) {
+    int skipcnt = 0;
+    unsigned char vencoding = 0;
+    long long vll = 0;
+    size_t zlbytes = ziplistBlobLen(zl);
+
+    while (p[0] != ZIP_END) {
+        struct zlentry e;
+        unsigned char *q;
+
+        assert(zipEntrySafe(zl, zlbytes, p, &e, 1));
+        q = p + e.prevrawlensize + e.lensize;
+
+        if (skipcnt == 0) {
+            /* Compare current entry with specified entry */
+            if (ZIP_IS_STR(e.encoding)) {
+                if (e.len == vlen && memcmp(q, vstr, vlen) == 0) {
+                    return p;
+                }
+            } else {
+                /* Find out if the searched field can be encoded. Note that
+                 * we do it only the first time, once done vencoding is set
+                 * to non-zero and vll is set to the integer value. */
+                if (vencoding == 0) {
+                    if (!zipTryEncoding(vstr, vlen, &vll, &vencoding)) {
+                        /* If the entry can't be encoded we set it to
+                         * UCHAR_MAX so that we don't retry again the next
+                         * time. */
+                        vencoding = UCHAR_MAX;
+                    }
+                    /* Must be non-zero by now */
+                    assert(vencoding);
+                }
+
+                /* Compare current entry with specified entry, do it only
+                 * if vencoding != UCHAR_MAX because if there is no encoding
+                 * possible for the field it can't be a valid integer. */
+                if (vencoding != UCHAR_MAX) {
+                    long long ll = zipLoadInteger(q, e.encoding);
+                    if (ll == vll) {
+                        return p;
+                    }
+                }
+            }
+
+            /* Reset skip count */
+            skipcnt = skip;
+        } else {
+            /* Skip entry */
+            skipcnt--;
+        }
+
+        /* Move to next entry */
+        p = q + e.len;
+    }
+
+    return NULL;
+}
+
+/* Return length of ziplist. */
+unsigned int ziplistLen(unsigned char *zl) {
+    unsigned int len = 0;
+    if (intrev16ifbe(ZIPLIST_LENGTH(zl)) < UINT16_MAX) {
+        len = intrev16ifbe(ZIPLIST_LENGTH(zl));
+    } else {
+        unsigned char *p = zl+ZIPLIST_HEADER_SIZE;
+        size_t zlbytes = intrev32ifbe(ZIPLIST_BYTES(zl));
+        while (*p != ZIP_END) {
+            p += zipRawEntryLengthSafe(zl, zlbytes, p);
+            len++;
+        }
+
+        /* Re-store length if small enough */
+        if (len < UINT16_MAX) ZIPLIST_LENGTH(zl) = intrev16ifbe(len);
+    }
+    return len;
+}
+
+/* Return ziplist blob size in bytes. */
+size_t ziplistBlobLen(unsigned char *zl) {
+    return intrev32ifbe(ZIPLIST_BYTES(zl));
+}
+
+void ziplistRepr(unsigned char *zl) {
+    unsigned char *p;
+    int index = 0;
+    zlentry entry;
+    size_t zlbytes = ziplistBlobLen(zl);
+
+    printf(
+        "{total bytes %u} "
+        "{num entries %u}\n"
+        "{tail offset %u}\n",
+        intrev32ifbe(ZIPLIST_BYTES(zl)),
+        intrev16ifbe(ZIPLIST_LENGTH(zl)),
+        intrev32ifbe(ZIPLIST_TAIL_OFFSET(zl)));
+    p = ZIPLIST_ENTRY_HEAD(zl);
+    while(*p != ZIP_END) {
+        assert(zipEntrySafe(zl, zlbytes, p, &entry, 1));
+        printf(
+            "{\n"
+                "\taddr 0x%08lx,\n"
+                "\tindex %2d,\n"
+                "\toffset %5lu,\n"
+                "\thdr+entry len: %5u,\n"
+                "\thdr len%2u,\n"
+                "\tprevrawlen: %5u,\n"
+                "\tprevrawlensize: %2u,\n"
+                "\tpayload %5u\n",
+            (long unsigned)p,
+            index,
+            (unsigned long) (p-zl),
+            entry.headersize+entry.len,
+            entry.headersize,
+            entry.prevrawlen,
+            entry.prevrawlensize,
+            entry.len);
+        printf("\tbytes: ");
+        for (unsigned int i = 0; i < entry.headersize+entry.len; i++) {
+            printf("%02x|",p[i]);
+        }
+        printf("\n");
+        p += entry.headersize;
+        if (ZIP_IS_STR(entry.encoding)) {
+            printf("\t[str]");
+            if (entry.len > 40) {
+                if (fwrite(p,40,1,stdout) == 0) perror("fwrite");
+                printf("...");
+            } else {
+                if (entry.len &&
+                    fwrite(p,entry.len,1,stdout) == 0) perror("fwrite");
+            }
+        } else {
+            printf("\t[int]%lld", (long long) zipLoadInteger(p,entry.encoding));
+        }
+        printf("\n}\n");
+        p += entry.len;
+        index++;
+    }
+    printf("{end}\n\n");
+}
+
+/* Validate the integrity of the data structure.
+ * when `deep` is 0, only the integrity of the header is validated.
+ * when `deep` is 1, we scan all the entries one by one. */
+int ziplistValidateIntegrity(unsigned char *zl, size_t size, int deep,
+    ziplistValidateEntryCB entry_cb, void *cb_userdata) {
+    /* check that we can actually read the header. (and ZIP_END) */
+    if (size < ZIPLIST_HEADER_SIZE + ZIPLIST_END_SIZE)
+        return 0;
+
+    /* check that the encoded size in the header must match the allocated size. */
+    size_t bytes = intrev32ifbe(ZIPLIST_BYTES(zl));
+    if (bytes != size)
+        return 0;
+
+    /* the last byte must be the terminator. */
+    if (zl[size - ZIPLIST_END_SIZE] != ZIP_END)
+        return 0;
+
+    /* make sure the tail offset isn't reaching outside the allocation. */
+    if (intrev32ifbe(ZIPLIST_TAIL_OFFSET(zl)) > size - ZIPLIST_END_SIZE)
+        return 0;
+
+    if (!deep)
+        return 1;
+
+    unsigned int count = 0;
+    unsigned int header_count = intrev16ifbe(ZIPLIST_LENGTH(zl));
+    unsigned char *p = ZIPLIST_ENTRY_HEAD(zl);
+    unsigned char *prev = NULL;
+    size_t prev_raw_size = 0;
+    while(*p != ZIP_END) {
+        struct zlentry e;
+        /* Decode the entry headers and fail if invalid or reaches outside the allocation */
+        if (!zipEntrySafe(zl, size, p, &e, 1))
+            return 0;
+
+        /* Make sure the record stating the prev entry size is correct. */
+        if (e.prevrawlen != prev_raw_size)
+            return 0;
+
+        /* Optionally let the caller validate the entry too. */
+        if (entry_cb && !entry_cb(p, header_count, cb_userdata))
+            return 0;
+
+        /* Move to the next entry */
+        prev_raw_size = e.headersize + e.len;
+        prev = p;
+        p += e.headersize + e.len;
+        count++;
+    }
+
+    /* Make sure 'p' really does point to the end of the ziplist. */
+    if (p != zl + bytes - ZIPLIST_END_SIZE)
+        return 0;
+
+    /* Make sure the <zltail> entry really do point to the start of the last entry. */
+    if (prev != NULL && prev != ZIPLIST_ENTRY_TAIL(zl))
+        return 0;
+
+    /* Check that the count in the header is correct */
+    if (header_count != UINT16_MAX && count != header_count)
+        return 0;
+
+    return 1;
+}
+
+/* Randomly select a pair of key and value.
+ * total_count is a pre-computed length/2 of the ziplist (to avoid calls to ziplistLen)
+ * 'key' and 'val' are used to store the result key value pair.
+ * 'val' can be NULL if the value is not needed. */
+void ziplistRandomPair(unsigned char *zl, unsigned long total_count, ziplistEntry *key, ziplistEntry *val) {
+    int ret;
+    unsigned char *p;
+
+    /* Avoid div by zero on corrupt ziplist */
+    assert(total_count);
+
+    /* Generate even numbers, because ziplist saved K-V pair */
+    int r = (rand() % total_count) * 2;
+    p = ziplistIndex(zl, r);
+    ret = ziplistGet(p, &key->sval, &key->slen, &key->lval);
+    assert(ret != 0);
+
+    if (!val)
+        return;
+    p = ziplistNext(zl, p);
+    ret = ziplistGet(p, &val->sval, &val->slen, &val->lval);
+    assert(ret != 0);
+}
+
+/* int compare for qsort */
+int uintCompare(const void *a, const void *b) {
+    return (*(unsigned int *) a - *(unsigned int *) b);
+}
+
+/* Helper method to store a string into from val or lval into dest */
+static inline void ziplistSaveValue(unsigned char *val, unsigned int len, long long lval, ziplistEntry *dest) {
+    dest->sval = val;
+    dest->slen = len;
+    dest->lval = lval;
+}
+
+/* Randomly select count of key value pairs and store into 'keys' and
+ * 'vals' args. The order of the picked entries is random, and the selections
+ * are non-unique (repetitions are possible).
+ * The 'vals' arg can be NULL in which case we skip these. */
+void ziplistRandomPairs(unsigned char *zl, unsigned int count, ziplistEntry *keys, ziplistEntry *vals) {
+    unsigned char *p, *key, *value;
+    unsigned int klen = 0, vlen = 0;
+    long long klval = 0, vlval = 0;
+
+    /* Notice: the index member must be first due to the use in uintCompare */
+    typedef struct {
+        unsigned int index;
+        unsigned int order;
+    } rand_pick;
+    rand_pick *picks = zmalloc(sizeof(rand_pick)*count);
+    unsigned int total_size = ziplistLen(zl)/2;
+
+    /* Avoid div by zero on corrupt ziplist */
+    assert(total_size);
+
+    /* create a pool of random indexes (some may be duplicate). */
+    for (unsigned int i = 0; i < count; i++) {
+        picks[i].index = (rand() % total_size) * 2; /* Generate even indexes */
+        /* keep track of the order we picked them */
+        picks[i].order = i;
+    }
+
+    /* sort by indexes. */
+    qsort(picks, count, sizeof(rand_pick), uintCompare);
+
+    /* fetch the elements form the ziplist into a output array respecting the original order. */
+    unsigned int zipindex = picks[0].index, pickindex = 0;
+    p = ziplistIndex(zl, zipindex);
+    while (ziplistGet(p, &key, &klen, &klval) && pickindex < count) {
+        p = ziplistNext(zl, p);
+        assert(ziplistGet(p, &value, &vlen, &vlval));
+        while (pickindex < count && zipindex == picks[pickindex].index) {
+            int storeorder = picks[pickindex].order;
+            ziplistSaveValue(key, klen, klval, &keys[storeorder]);
+            if (vals)
+                ziplistSaveValue(value, vlen, vlval, &vals[storeorder]);
+             pickindex++;
+        }
+        zipindex += 2;
+        p = ziplistNext(zl, p);
+    }
+
+    zfree(picks);
+}
+
+/* Randomly select count of key value pairs and store into 'keys' and
+ * 'vals' args. The selections are unique (no repetitions), and the order of
+ * the picked entries is NOT-random.
+ * The 'vals' arg can be NULL in which case we skip these.
+ * The return value is the number of items picked which can be lower than the
+ * requested count if the ziplist doesn't hold enough pairs. */
+unsigned int ziplistRandomPairsUnique(unsigned char *zl, unsigned int count, ziplistEntry *keys, ziplistEntry *vals) {
+    unsigned char *p, *key;
+    unsigned int klen = 0;
+    long long klval = 0;
+    unsigned int total_size = ziplistLen(zl)/2;
+    unsigned int index = 0;
+    if (count > total_size)
+        count = total_size;
+
+    /* To only iterate once, every time we try to pick a member, the probability
+     * we pick it is the quotient of the count left we want to pick and the
+     * count still we haven't visited in the dict, this way, we could make every
+     * member be equally picked.*/
+    p = ziplistIndex(zl, 0);
+    unsigned int picked = 0, remaining = count;
+    while (picked < count && p) {
+        double randomDouble = ((double)rand()) / RAND_MAX;
+        double threshold = ((double)remaining) / (total_size - index);
+        if (randomDouble <= threshold) {
+            assert(ziplistGet(p, &key, &klen, &klval));
+            ziplistSaveValue(key, klen, klval, &keys[picked]);
+            p = ziplistNext(zl, p);
+            assert(p);
+            if (vals) {
+                assert(ziplistGet(p, &key, &klen, &klval));
+                ziplistSaveValue(key, klen, klval, &vals[picked]);
+            }
+            remaining--;
+            picked++;
+        } else {
+            p = ziplistNext(zl, p);
+            assert(p);
+        }
+        p = ziplistNext(zl, p);
+        index++;
+    }
+    return picked;
+}
+
+#ifdef REDIS_TEST
+#include <sys/time.h>
+#include "adlist.h"
+#include "sds.h"
+#include "testhelp.h"
+
+#define debug(f, ...) { if (DEBUG) printf(f, __VA_ARGS__); }
+
+static unsigned char *createList(void) {
+    unsigned char *zl = ziplistNew();
+    zl = ziplistPush(zl, (unsigned char*)"foo", 3, ZIPLIST_TAIL);
+    zl = ziplistPush(zl, (unsigned char*)"quux", 4, ZIPLIST_TAIL);
+    zl = ziplistPush(zl, (unsigned char*)"hello", 5, ZIPLIST_HEAD);
+    zl = ziplistPush(zl, (unsigned char*)"1024", 4, ZIPLIST_TAIL);
+    return zl;
+}
+
+static unsigned char *createIntList(void) {
+    unsigned char *zl = ziplistNew();
+    char buf[32];
+
+    snprintf(buf, sizeof(buf), "100");
+    zl = ziplistPush(zl, (unsigned char*)buf, strlen(buf), ZIPLIST_TAIL);
+    snprintf(buf, sizeof(buf), "128000");
+    zl = ziplistPush(zl, (unsigned char*)buf, strlen(buf), ZIPLIST_TAIL);
+    snprintf(buf, sizeof(buf), "-100");
+    zl = ziplistPush(zl, (unsigned char*)buf, strlen(buf), ZIPLIST_HEAD);
+    snprintf(buf, sizeof(buf), "4294967296");
+    zl = ziplistPush(zl, (unsigned char*)buf, strlen(buf), ZIPLIST_HEAD);
+    snprintf(buf, sizeof(buf), "non integer");
+    zl = ziplistPush(zl, (unsigned char*)buf, strlen(buf), ZIPLIST_TAIL);
+    snprintf(buf,sizeof(buf), "much much longer non integer");
+    zl = ziplistPush(zl, (unsigned char*)buf, strlen(buf), ZIPLIST_TAIL);
+    return zl;
+}
+
+static long long usec(void) {
+    struct timeval tv;
+    gettimeofday(&tv,NULL);
+    return (((long long)tv.tv_sec)*1000000)+tv.tv_usec;
+}
+
+static void stress(int pos, int num, int maxsize, int dnum) {
+    int i,j,k;
+    unsigned char *zl;
+    char posstr[2][5] = { "HEAD", "TAIL" };
+    long long start;
+    for (i = 0; i < maxsize; i+=dnum) {
+        zl = ziplistNew();
+        for (j = 0; j < i; j++) {
+            zl = ziplistPush(zl,(unsigned char*)"quux",4,ZIPLIST_TAIL);
+        }
+
+        /* Do num times a push+pop from pos */
+        start = usec();
+        for (k = 0; k < num; k++) {
+            zl = ziplistPush(zl,(unsigned char*)"quux",4,pos);
+            zl = ziplistDeleteRange(zl,0,1);
+        }
+        printf("List size: %8d, bytes: %8d, %dx push+pop (%s): %6lld usec\n",
+            i,intrev32ifbe(ZIPLIST_BYTES(zl)),num,posstr[pos],usec()-start);
+        zfree(zl);
+    }
+}
+
+static unsigned char *pop(unsigned char *zl, int where) {
+    unsigned char *p, *vstr;
+    unsigned int vlen;
+    long long vlong = 0;
+
+    p = ziplistIndex(zl,where == ZIPLIST_HEAD ? 0 : -1);
+    if (ziplistGet(p,&vstr,&vlen,&vlong)) {
+        if (where == ZIPLIST_HEAD)
+            printf("Pop head: ");
+        else
+            printf("Pop tail: ");
+
+        if (vstr) {
+            if (vlen && fwrite(vstr,vlen,1,stdout) == 0) perror("fwrite");
+        }
+        else {
+            printf("%lld", vlong);
+        }
+
+        printf("\n");
+        return ziplistDelete(zl,&p);
+    } else {
+        printf("ERROR: Could not pop\n");
+        exit(1);
+    }
+}
+
+static int randstring(char *target, unsigned int min, unsigned int max) {
+    int p = 0;
+    int len = min+rand()%(max-min+1);
+    int minval, maxval;
+    switch(rand() % 3) {
+    case 0:
+        minval = 0;
+        maxval = 255;
+    break;
+    case 1:
+        minval = 48;
+        maxval = 122;
+    break;
+    case 2:
+        minval = 48;
+        maxval = 52;
+    break;
+    default:
+        assert(NULL);
+    }
+
+    while(p < len)
+        target[p++] = minval+rand()%(maxval-minval+1);
+    return len;
+}
+
+static void verify(unsigned char *zl, zlentry *e) {
+    int len = ziplistLen(zl);
+    zlentry _e;
+
+    ZIPLIST_ENTRY_ZERO(&_e);
+
+    for (int i = 0; i < len; i++) {
+        memset(&e[i], 0, sizeof(zlentry));
+        zipEntry(ziplistIndex(zl, i), &e[i]);
+
+        memset(&_e, 0, sizeof(zlentry));
+        zipEntry(ziplistIndex(zl, -len+i), &_e);
+
+        assert(memcmp(&e[i], &_e, sizeof(zlentry)) == 0);
+    }
+}
+
+static unsigned char *insertHelper(unsigned char *zl, char ch, size_t len, unsigned char *pos) {
+    assert(len <= ZIP_BIG_PREVLEN);
+    unsigned char data[ZIP_BIG_PREVLEN] = {0};
+    memset(data, ch, len);
+    return ziplistInsert(zl, pos, data, len);
+}
+
+static int compareHelper(unsigned char *zl, char ch, size_t len, int index) {
+    assert(len <= ZIP_BIG_PREVLEN);
+    unsigned char data[ZIP_BIG_PREVLEN] = {0};
+    memset(data, ch, len);
+    unsigned char *p = ziplistIndex(zl, index);
+    assert(p != NULL);
+    return ziplistCompare(p, data, len);
+}
+
+static size_t strEntryBytesSmall(size_t slen) {
+    return slen + zipStorePrevEntryLength(NULL, 0) + zipStoreEntryEncoding(NULL, 0, slen);
+}
+
+static size_t strEntryBytesLarge(size_t slen) {
+    return slen + zipStorePrevEntryLength(NULL, ZIP_BIG_PREVLEN) + zipStoreEntryEncoding(NULL, 0, slen);
+}
+
+/* ./redis-server test ziplist <randomseed> */
+int ziplistTest(int argc, char **argv, int flags) {
+    int accurate = (flags & REDIS_TEST_ACCURATE);
+    unsigned char *zl, *p;
+    unsigned char *entry;
+    unsigned int elen;
+    long long value;
+    int iteration;
+
+    /* If an argument is given, use it as the random seed. */
+    if (argc >= 4)
+        srand(atoi(argv[3]));
+
+    zl = createIntList();
+    ziplistRepr(zl);
+
+    zfree(zl);
+
+    zl = createList();
+    ziplistRepr(zl);
+
+    zl = pop(zl,ZIPLIST_TAIL);
+    ziplistRepr(zl);
+
+    zl = pop(zl,ZIPLIST_HEAD);
+    ziplistRepr(zl);
+
+    zl = pop(zl,ZIPLIST_TAIL);
+    ziplistRepr(zl);
+
+    zl = pop(zl,ZIPLIST_TAIL);
+    ziplistRepr(zl);
+
+    zfree(zl);
+
+    printf("Get element at index 3:\n");
+    {
+        zl = createList();
+        p = ziplistIndex(zl, 3);
+        if (!ziplistGet(p, &entry, &elen, &value)) {
+            printf("ERROR: Could not access index 3\n");
+            return 1;
+        }
+        if (entry) {
+            if (elen && fwrite(entry,elen,1,stdout) == 0) perror("fwrite");
+            printf("\n");
+        } else {
+            printf("%lld\n", value);
+        }
+        printf("\n");
+        zfree(zl);
+    }
+
+    printf("Get element at index 4 (out of range):\n");
+    {
+        zl = createList();
+        p = ziplistIndex(zl, 4);
+        if (p == NULL) {
+            printf("No entry\n");
+        } else {
+            printf("ERROR: Out of range index should return NULL, returned offset: %ld\n", (long)(p-zl));
+            return 1;
+        }
+        printf("\n");
+        zfree(zl);
+    }
+
+    printf("Get element at index -1 (last element):\n");
+    {
+        zl = createList();
+        p = ziplistIndex(zl, -1);
+        if (!ziplistGet(p, &entry, &elen, &value)) {
+            printf("ERROR: Could not access index -1\n");
+            return 1;
+        }
+        if (entry) {
+            if (elen && fwrite(entry,elen,1,stdout) == 0) perror("fwrite");
+            printf("\n");
+        } else {
+            printf("%lld\n", value);
+        }
+        printf("\n");
+        zfree(zl);
+    }
+
+    printf("Get element at index -4 (first element):\n");
+    {
+        zl = createList();
+        p = ziplistIndex(zl, -4);
+        if (!ziplistGet(p, &entry, &elen, &value)) {
+            printf("ERROR: Could not access index -4\n");
+            return 1;
+        }
+        if (entry) {
+            if (elen && fwrite(entry,elen,1,stdout) == 0) perror("fwrite");
+            printf("\n");
+        } else {
+            printf("%lld\n", value);
+        }
+        printf("\n");
+        zfree(zl);
+    }
+
+    printf("Get element at index -5 (reverse out of range):\n");
+    {
+        zl = createList();
+        p = ziplistIndex(zl, -5);
+        if (p == NULL) {
+            printf("No entry\n");
+        } else {
+            printf("ERROR: Out of range index should return NULL, returned offset: %ld\n", (long)(p-zl));
+            return 1;
+        }
+        printf("\n");
+        zfree(zl);
+    }
+
+    printf("Iterate list from 0 to end:\n");
+    {
+        zl = createList();
+        p = ziplistIndex(zl, 0);
+        while (ziplistGet(p, &entry, &elen, &value)) {
+            printf("Entry: ");
+            if (entry) {
+                if (elen && fwrite(entry,elen,1,stdout) == 0) perror("fwrite");
+            } else {
+                printf("%lld", value);
+            }
+            p = ziplistNext(zl,p);
+            printf("\n");
+        }
+        printf("\n");
+        zfree(zl);
+    }
+
+    printf("Iterate list from 1 to end:\n");
+    {
+        zl = createList();
+        p = ziplistIndex(zl, 1);
+        while (ziplistGet(p, &entry, &elen, &value)) {
+            printf("Entry: ");
+            if (entry) {
+                if (elen && fwrite(entry,elen,1,stdout) == 0) perror("fwrite");
+            } else {
+                printf("%lld", value);
+            }
+            p = ziplistNext(zl,p);
+            printf("\n");
+        }
+        printf("\n");
+        zfree(zl);
+    }
+
+    printf("Iterate list from 2 to end:\n");
+    {
+        zl = createList();
+        p = ziplistIndex(zl, 2);
+        while (ziplistGet(p, &entry, &elen, &value)) {
+            printf("Entry: ");
+            if (entry) {
+                if (elen && fwrite(entry,elen,1,stdout) == 0) perror("fwrite");
+            } else {
+                printf("%lld", value);
+            }
+            p = ziplistNext(zl,p);
+            printf("\n");
+        }
+        printf("\n");
+        zfree(zl);
+    }
+
+    printf("Iterate starting out of range:\n");
+    {
+        zl = createList();
+        p = ziplistIndex(zl, 4);
+        if (!ziplistGet(p, &entry, &elen, &value)) {
+            printf("No entry\n");
+        } else {
+            printf("ERROR\n");
+        }
+        printf("\n");
+        zfree(zl);
+    }
+
+    printf("Iterate from back to front:\n");
+    {
+        zl = createList();
+        p = ziplistIndex(zl, -1);
+        while (ziplistGet(p, &entry, &elen, &value)) {
+            printf("Entry: ");
+            if (entry) {
+                if (elen && fwrite(entry,elen,1,stdout) == 0) perror("fwrite");
+            } else {
+                printf("%lld", value);
+            }
+            p = ziplistPrev(zl,p);
+            printf("\n");
+        }
+        printf("\n");
+        zfree(zl);
+    }
+
+    printf("Iterate from back to front, deleting all items:\n");
+    {
+        zl = createList();
+        p = ziplistIndex(zl, -1);
+        while (ziplistGet(p, &entry, &elen, &value)) {
+            printf("Entry: ");
+            if (entry) {
+                if (elen && fwrite(entry,elen,1,stdout) == 0) perror("fwrite");
+            } else {
+                printf("%lld", value);
+            }
+            zl = ziplistDelete(zl,&p);
+            p = ziplistPrev(zl,p);
+            printf("\n");
+        }
+        printf("\n");
+        zfree(zl);
+    }
+
+    printf("Delete inclusive range 0,0:\n");
+    {
+        zl = createList();
+        zl = ziplistDeleteRange(zl, 0, 1);
+        ziplistRepr(zl);
+        zfree(zl);
+    }
+
+    printf("Delete inclusive range 0,1:\n");
+    {
+        zl = createList();
+        zl = ziplistDeleteRange(zl, 0, 2);
+        ziplistRepr(zl);
+        zfree(zl);
+    }
+
+    printf("Delete inclusive range 1,2:\n");
+    {
+        zl = createList();
+        zl = ziplistDeleteRange(zl, 1, 2);
+        ziplistRepr(zl);
+        zfree(zl);
+    }
+
+    printf("Delete with start index out of range:\n");
+    {
+        zl = createList();
+        zl = ziplistDeleteRange(zl, 5, 1);
+        ziplistRepr(zl);
+        zfree(zl);
+    }
+
+    printf("Delete with num overflow:\n");
+    {
+        zl = createList();
+        zl = ziplistDeleteRange(zl, 1, 5);
+        ziplistRepr(zl);
+        zfree(zl);
+    }
+
+    printf("Delete foo while iterating:\n");
+    {
+        zl = createList();
+        p = ziplistIndex(zl,0);
+        while (ziplistGet(p,&entry,&elen,&value)) {
+            if (entry && strncmp("foo",(char*)entry,elen) == 0) {
+                printf("Delete foo\n");
+                zl = ziplistDelete(zl,&p);
+            } else {
+                printf("Entry: ");
+                if (entry) {
+                    if (elen && fwrite(entry,elen,1,stdout) == 0)
+                        perror("fwrite");
+                } else {
+                    printf("%lld",value);
+                }
+                p = ziplistNext(zl,p);
+                printf("\n");
+            }
+        }
+        printf("\n");
+        ziplistRepr(zl);
+        zfree(zl);
+    }
+
+    printf("Replace with same size:\n");
+    {
+        zl = createList(); /* "hello", "foo", "quux", "1024" */
+        unsigned char *orig_zl = zl;
+        p = ziplistIndex(zl, 0);
+        zl = ziplistReplace(zl, p, (unsigned char*)"zoink", 5);
+        p = ziplistIndex(zl, 3);
+        zl = ziplistReplace(zl, p, (unsigned char*)"yy", 2);
+        p = ziplistIndex(zl, 1);
+        zl = ziplistReplace(zl, p, (unsigned char*)"65536", 5);
+        p = ziplistIndex(zl, 0);
+        assert(!memcmp((char*)p,
+                       "\x00\x05zoink"
+                       "\x07\xf0\x00\x00\x01" /* 65536 as int24 */
+                       "\x05\x04quux" "\x06\x02yy" "\xff",
+                       23));
+        assert(zl == orig_zl); /* no reallocations have happened */
+        zfree(zl);
+        printf("SUCCESS\n\n");
+    }
+
+    printf("Replace with different size:\n");
+    {
+        zl = createList(); /* "hello", "foo", "quux", "1024" */
+        p = ziplistIndex(zl, 1);
+        zl = ziplistReplace(zl, p, (unsigned char*)"squirrel", 8);
+        p = ziplistIndex(zl, 0);
+        assert(!strncmp((char*)p,
+                        "\x00\x05hello" "\x07\x08squirrel" "\x0a\x04quux"
+                        "\x06\xc0\x00\x04" "\xff",
+                        28));
+        zfree(zl);
+        printf("SUCCESS\n\n");
+    }
+
+    printf("Regression test for >255 byte strings:\n");
+    {
+        char v1[257] = {0}, v2[257] = {0};
+        memset(v1,'x',256);
+        memset(v2,'y',256);
+        zl = ziplistNew();
+        zl = ziplistPush(zl,(unsigned char*)v1,strlen(v1),ZIPLIST_TAIL);
+        zl = ziplistPush(zl,(unsigned char*)v2,strlen(v2),ZIPLIST_TAIL);
+
+        /* Pop values again and compare their value. */
+        p = ziplistIndex(zl,0);
+        assert(ziplistGet(p,&entry,&elen,&value));
+        assert(strncmp(v1,(char*)entry,elen) == 0);
+        p = ziplistIndex(zl,1);
+        assert(ziplistGet(p,&entry,&elen,&value));
+        assert(strncmp(v2,(char*)entry,elen) == 0);
+        printf("SUCCESS\n\n");
+        zfree(zl);
+    }
+
+    printf("Regression test deleting next to last entries:\n");
+    {
+        char v[3][257] = {{0}};
+        zlentry e[3] = {{.prevrawlensize = 0, .prevrawlen = 0, .lensize = 0,
+                         .len = 0, .headersize = 0, .encoding = 0, .p = NULL}};
+        size_t i;
+
+        for (i = 0; i < (sizeof(v)/sizeof(v[0])); i++) {
+            memset(v[i], 'a' + i, sizeof(v[0]));
+        }
+
+        v[0][256] = '\0';
+        v[1][  1] = '\0';
+        v[2][256] = '\0';
+
+        zl = ziplistNew();
+        for (i = 0; i < (sizeof(v)/sizeof(v[0])); i++) {
+            zl = ziplistPush(zl, (unsigned char *) v[i], strlen(v[i]), ZIPLIST_TAIL);
+        }
+
+        verify(zl, e);
+
+        assert(e[0].prevrawlensize == 1);
+        assert(e[1].prevrawlensize == 5);
+        assert(e[2].prevrawlensize == 1);
+
+        /* Deleting entry 1 will increase `prevrawlensize` for entry 2 */
+        unsigned char *p = e[1].p;
+        zl = ziplistDelete(zl, &p);
+
+        verify(zl, e);
+
+        assert(e[0].prevrawlensize == 1);
+        assert(e[1].prevrawlensize == 5);
+
+        printf("SUCCESS\n\n");
+        zfree(zl);
+    }
+
+    printf("Create long list and check indices:\n");
+    {
+        unsigned long long start = usec();
+        zl = ziplistNew();
+        char buf[32];
+        int i,len;
+        for (i = 0; i < 1000; i++) {
+            len = snprintf(buf,sizeof(buf),"%d",i);
+            zl = ziplistPush(zl,(unsigned char*)buf,len,ZIPLIST_TAIL);
+        }
+        for (i = 0; i < 1000; i++) {
+            p = ziplistIndex(zl,i);
+            assert(ziplistGet(p,NULL,NULL,&value));
+            assert(i == value);
+
+            p = ziplistIndex(zl,-i-1);
+            assert(ziplistGet(p,NULL,NULL,&value));
+            assert(999-i == value);
+        }
+        printf("SUCCESS. usec=%lld\n\n", usec()-start);
+        zfree(zl);
+    }
+
+    printf("Compare strings with ziplist entries:\n");
+    {
+        zl = createList();
+        p = ziplistIndex(zl,0);
+        if (!ziplistCompare(p,(unsigned char*)"hello",5)) {
+            printf("ERROR: not \"hello\"\n");
+            return 1;
+        }
+        if (ziplistCompare(p,(unsigned char*)"hella",5)) {
+            printf("ERROR: \"hella\"\n");
+            return 1;
+        }
+
+        p = ziplistIndex(zl,3);
+        if (!ziplistCompare(p,(unsigned char*)"1024",4)) {
+            printf("ERROR: not \"1024\"\n");
+            return 1;
+        }
+        if (ziplistCompare(p,(unsigned char*)"1025",4)) {
+            printf("ERROR: \"1025\"\n");
+            return 1;
+        }
+        printf("SUCCESS\n\n");
+        zfree(zl);
+    }
+
+    printf("Merge test:\n");
+    {
+        /* create list gives us: [hello, foo, quux, 1024] */
+        zl = createList();
+        unsigned char *zl2 = createList();
+
+        unsigned char *zl3 = ziplistNew();
+        unsigned char *zl4 = ziplistNew();
+
+        if (ziplistMerge(&zl4, &zl4)) {
+            printf("ERROR: Allowed merging of one ziplist into itself.\n");
+            return 1;
+        }
+
+        /* Merge two empty ziplists, get empty result back. */
+        zl4 = ziplistMerge(&zl3, &zl4);
+        ziplistRepr(zl4);
+        if (ziplistLen(zl4)) {
+            printf("ERROR: Merging two empty ziplists created entries.\n");
+            return 1;
+        }
+        zfree(zl4);
+
+        zl2 = ziplistMerge(&zl, &zl2);
+        /* merge gives us: [hello, foo, quux, 1024, hello, foo, quux, 1024] */
+        ziplistRepr(zl2);
+
+        if (ziplistLen(zl2) != 8) {
+            printf("ERROR: Merged length not 8, but: %u\n", ziplistLen(zl2));
+            return 1;
+        }
+
+        p = ziplistIndex(zl2,0);
+        if (!ziplistCompare(p,(unsigned char*)"hello",5)) {
+            printf("ERROR: not \"hello\"\n");
+            return 1;
+        }
+        if (ziplistCompare(p,(unsigned char*)"hella",5)) {
+            printf("ERROR: \"hella\"\n");
+            return 1;
+        }
+
+        p = ziplistIndex(zl2,3);
+        if (!ziplistCompare(p,(unsigned char*)"1024",4)) {
+            printf("ERROR: not \"1024\"\n");
+            return 1;
+        }
+        if (ziplistCompare(p,(unsigned char*)"1025",4)) {
+            printf("ERROR: \"1025\"\n");
+            return 1;
+        }
+
+        p = ziplistIndex(zl2,4);
+        if (!ziplistCompare(p,(unsigned char*)"hello",5)) {
+            printf("ERROR: not \"hello\"\n");
+            return 1;
+        }
+        if (ziplistCompare(p,(unsigned char*)"hella",5)) {
+            printf("ERROR: \"hella\"\n");
+            return 1;
+        }
+
+        p = ziplistIndex(zl2,7);
+        if (!ziplistCompare(p,(unsigned char*)"1024",4)) {
+            printf("ERROR: not \"1024\"\n");
+            return 1;
+        }
+        if (ziplistCompare(p,(unsigned char*)"1025",4)) {
+            printf("ERROR: \"1025\"\n");
+            return 1;
+        }
+        printf("SUCCESS\n\n");
+        zfree(zl);
+    }
+
+    printf("Stress with random payloads of different encoding:\n");
+    {
+        unsigned long long start = usec();
+        int i,j,len,where;
+        unsigned char *p;
+        char buf[1024];
+        int buflen;
+        list *ref;
+        listNode *refnode;
+
+        /* Hold temp vars from ziplist */
+        unsigned char *sstr;
+        unsigned int slen;
+        long long sval;
+
+        iteration = accurate ? 20000 : 20;
+        for (i = 0; i < iteration; i++) {
+            zl = ziplistNew();
+            ref = listCreate();
+            listSetFreeMethod(ref,(void (*)(void*))sdsfree);
+            len = rand() % 256;
+
+            /* Create lists */
+            for (j = 0; j < len; j++) {
+                where = (rand() & 1) ? ZIPLIST_HEAD : ZIPLIST_TAIL;
+                if (rand() % 2) {
+                    buflen = randstring(buf,1,sizeof(buf)-1);
+                } else {
+                    switch(rand() % 3) {
+                    case 0:
+                        buflen = snprintf(buf,sizeof(buf),"%lld",(0LL + rand()) >> 20);
+                        break;
+                    case 1:
+                        buflen = snprintf(buf,sizeof(buf),"%lld",(0LL + rand()));
+                        break;
+                    case 2:
+                        buflen = snprintf(buf,sizeof(buf),"%lld",(0LL + rand()) << 20);
+                        break;
+                    default:
+                        assert(NULL);
+                    }
+                }
+
+                /* Add to ziplist */
+                zl = ziplistPush(zl, (unsigned char*)buf, buflen, where);
+
+                /* Add to reference list */
+                if (where == ZIPLIST_HEAD) {
+                    listAddNodeHead(ref,sdsnewlen(buf, buflen));
+                } else if (where == ZIPLIST_TAIL) {
+                    listAddNodeTail(ref,sdsnewlen(buf, buflen));
+                } else {
+                    assert(NULL);
+                }
+            }
+
+            assert(listLength(ref) == ziplistLen(zl));
+            for (j = 0; j < len; j++) {
+                /* Naive way to get elements, but similar to the stresser
+                 * executed from the Tcl test suite. */
+                p = ziplistIndex(zl,j);
+                refnode = listIndex(ref,j);
+
+                assert(ziplistGet(p,&sstr,&slen,&sval));
+                if (sstr == NULL) {
+                    buflen = snprintf(buf,sizeof(buf),"%lld",sval);
+                } else {
+                    buflen = slen;
+                    memcpy(buf,sstr,buflen);
+                    buf[buflen] = '\0';
+                }
+                assert(memcmp(buf,listNodeValue(refnode),buflen) == 0);
+            }
+            zfree(zl);
+            listRelease(ref);
+        }
+        printf("Done. usec=%lld\n\n", usec()-start);
+    }
+
+    printf("Stress with variable ziplist size:\n");
+    {
+        unsigned long long start = usec();
+        int maxsize = accurate ? 16384 : 16;
+        stress(ZIPLIST_HEAD,100000,maxsize,256);
+        stress(ZIPLIST_TAIL,100000,maxsize,256);
+        printf("Done. usec=%lld\n\n", usec()-start);
+    }
+
+    /* Benchmarks */
+    {
+        zl = ziplistNew();
+        iteration = accurate ? 100000 : 100;
+        for (int i=0; i<iteration; i++) {
+            char buf[4096] = "asdf";
+            zl = ziplistPush(zl, (unsigned char*)buf, 4, ZIPLIST_TAIL);
+            zl = ziplistPush(zl, (unsigned char*)buf, 40, ZIPLIST_TAIL);
+            zl = ziplistPush(zl, (unsigned char*)buf, 400, ZIPLIST_TAIL);
+            zl = ziplistPush(zl, (unsigned char*)buf, 4000, ZIPLIST_TAIL);
+            zl = ziplistPush(zl, (unsigned char*)"1", 1, ZIPLIST_TAIL);
+            zl = ziplistPush(zl, (unsigned char*)"10", 2, ZIPLIST_TAIL);
+            zl = ziplistPush(zl, (unsigned char*)"100", 3, ZIPLIST_TAIL);
+            zl = ziplistPush(zl, (unsigned char*)"1000", 4, ZIPLIST_TAIL);
+            zl = ziplistPush(zl, (unsigned char*)"10000", 5, ZIPLIST_TAIL);
+            zl = ziplistPush(zl, (unsigned char*)"100000", 6, ZIPLIST_TAIL);
+        }
+
+        printf("Benchmark ziplistFind:\n");
+        {
+            unsigned long long start = usec();
+            for (int i = 0; i < 2000; i++) {
+                unsigned char *fptr = ziplistIndex(zl, ZIPLIST_HEAD);
+                fptr = ziplistFind(zl, fptr, (unsigned char*)"nothing", 7, 1);
+            }
+            printf("%lld\n", usec()-start);
+        }
+
+        printf("Benchmark ziplistIndex:\n");
+        {
+            unsigned long long start = usec();
+            for (int i = 0; i < 2000; i++) {
+                ziplistIndex(zl, 99999);
+            }
+            printf("%lld\n", usec()-start);
+        }
+
+        printf("Benchmark ziplistValidateIntegrity:\n");
+        {
+            unsigned long long start = usec();
+            for (int i = 0; i < 2000; i++) {
+                ziplistValidateIntegrity(zl, ziplistBlobLen(zl), 1, NULL, NULL);
+            }
+            printf("%lld\n", usec()-start);
+        }
+
+        printf("Benchmark ziplistCompare with string\n");
+        {
+            unsigned long long start = usec();
+            for (int i = 0; i < 2000; i++) {
+                unsigned char *eptr = ziplistIndex(zl,0);
+                while (eptr != NULL) {
+                    ziplistCompare(eptr,(unsigned char*)"nothing",7);
+                    eptr = ziplistNext(zl,eptr);
+                }
+            }
+            printf("Done. usec=%lld\n", usec()-start);
+        }
+
+        printf("Benchmark ziplistCompare with number\n");
+        {
+            unsigned long long start = usec();
+            for (int i = 0; i < 2000; i++) {
+                unsigned char *eptr = ziplistIndex(zl,0);
+                while (eptr != NULL) {
+                    ziplistCompare(eptr,(unsigned char*)"99999",5);
+                    eptr = ziplistNext(zl,eptr);
+                }
+            }
+            printf("Done. usec=%lld\n", usec()-start);
+        }
+
+        zfree(zl);
+    }
+
+    printf("Stress __ziplistCascadeUpdate:\n");
+    {
+        char data[ZIP_BIG_PREVLEN];
+        zl = ziplistNew();
+        iteration = accurate ? 100000 : 100;
+        for (int i = 0; i < iteration; i++) {
+            zl = ziplistPush(zl, (unsigned char*)data, ZIP_BIG_PREVLEN-4, ZIPLIST_TAIL);
+        }
+        unsigned long long start = usec();
+        zl = ziplistPush(zl, (unsigned char*)data, ZIP_BIG_PREVLEN-3, ZIPLIST_HEAD);
+        printf("Done. usec=%lld\n\n", usec()-start);
+        zfree(zl);
+    }
+
+    printf("Edge cases of __ziplistCascadeUpdate:\n");
+    {
+        /* Inserting a entry with data length greater than ZIP_BIG_PREVLEN-4 
+         * will leads to cascade update. */
+        size_t s1 = ZIP_BIG_PREVLEN-4, s2 = ZIP_BIG_PREVLEN-3;
+        zl = ziplistNew();
+
+        zlentry e[4] = {{.prevrawlensize = 0, .prevrawlen = 0, .lensize = 0,
+                         .len = 0, .headersize = 0, .encoding = 0, .p = NULL}};
+
+        zl = insertHelper(zl, 'a', s1, ZIPLIST_ENTRY_HEAD(zl));
+        verify(zl, e);
+
+        assert(e[0].prevrawlensize == 1 && e[0].prevrawlen == 0);
+        assert(compareHelper(zl, 'a', s1, 0));
+        ziplistRepr(zl);
+
+        /* No expand. */
+        zl = insertHelper(zl, 'b', s1, ZIPLIST_ENTRY_HEAD(zl));
+        verify(zl, e);
+
+        assert(e[0].prevrawlensize == 1 && e[0].prevrawlen == 0);
+        assert(compareHelper(zl, 'b', s1, 0));
+
+        assert(e[1].prevrawlensize == 1 && e[1].prevrawlen == strEntryBytesSmall(s1));
+        assert(compareHelper(zl, 'a', s1, 1));
+
+        ziplistRepr(zl);
+
+        /* Expand(tail included). */
+        zl = insertHelper(zl, 'c', s2, ZIPLIST_ENTRY_HEAD(zl));
+        verify(zl, e);
+
+        assert(e[0].prevrawlensize == 1 && e[0].prevrawlen == 0);
+        assert(compareHelper(zl, 'c', s2, 0));
+
+        assert(e[1].prevrawlensize == 5 && e[1].prevrawlen == strEntryBytesSmall(s2));
+        assert(compareHelper(zl, 'b', s1, 1));
+
+        assert(e[2].prevrawlensize == 5 && e[2].prevrawlen == strEntryBytesLarge(s1));
+        assert(compareHelper(zl, 'a', s1, 2));
+
+        ziplistRepr(zl);
+
+        /* Expand(only previous head entry). */
+        zl = insertHelper(zl, 'd', s2, ZIPLIST_ENTRY_HEAD(zl));
+        verify(zl, e);
+
+        assert(e[0].prevrawlensize == 1 && e[0].prevrawlen == 0);
+        assert(compareHelper(zl, 'd', s2, 0));
+
+        assert(e[1].prevrawlensize == 5 && e[1].prevrawlen == strEntryBytesSmall(s2));
+        assert(compareHelper(zl, 'c', s2, 1));
+
+        assert(e[2].prevrawlensize == 5 && e[2].prevrawlen == strEntryBytesLarge(s2));
+        assert(compareHelper(zl, 'b', s1, 2));
+
+        assert(e[3].prevrawlensize == 5 && e[3].prevrawlen == strEntryBytesLarge(s1));
+        assert(compareHelper(zl, 'a', s1, 3));
+
+        ziplistRepr(zl);
+
+        /* Delete from mid. */
+        unsigned char *p = ziplistIndex(zl, 2);
+        zl = ziplistDelete(zl, &p);
+        verify(zl, e);
+
+        assert(e[0].prevrawlensize == 1 && e[0].prevrawlen == 0);
+        assert(compareHelper(zl, 'd', s2, 0));
+
+        assert(e[1].prevrawlensize == 5 && e[1].prevrawlen == strEntryBytesSmall(s2));
+        assert(compareHelper(zl, 'c', s2, 1));
+
+        assert(e[2].prevrawlensize == 5 && e[2].prevrawlen == strEntryBytesLarge(s2));
+        assert(compareHelper(zl, 'a', s1, 2));
+
+        ziplistRepr(zl);
+
+        zfree(zl);
+    }
+
+    printf("__ziplistInsert nextdiff == -4 && reqlen < 4 (issue #7170):\n");
+    {
+        zl = ziplistNew();
+
+        /* We set some values to almost reach the critical point - 254 */
+        char A_252[253] = {0}, A_250[251] = {0};
+        memset(A_252, 'A', 252);
+        memset(A_250, 'A', 250);
+
+        /* After the rpush, the list look like: [one two A_252 A_250 three 10] */
+        zl = ziplistPush(zl, (unsigned char*)"one", 3, ZIPLIST_TAIL);
+        zl = ziplistPush(zl, (unsigned char*)"two", 3, ZIPLIST_TAIL);
+        zl = ziplistPush(zl, (unsigned char*)A_252, strlen(A_252), ZIPLIST_TAIL);
+        zl = ziplistPush(zl, (unsigned char*)A_250, strlen(A_250), ZIPLIST_TAIL);
+        zl = ziplistPush(zl, (unsigned char*)"three", 5, ZIPLIST_TAIL);
+        zl = ziplistPush(zl, (unsigned char*)"10", 2, ZIPLIST_TAIL);
+        ziplistRepr(zl);
+
+        p = ziplistIndex(zl, 2);
+        if (!ziplistCompare(p, (unsigned char*)A_252, strlen(A_252))) {
+            printf("ERROR: not \"A_252\"\n");
+            return 1;
+        }
+
+        /* When we remove A_252, the list became: [one two A_250 three 10]
+         * A_250's prev node became node two, because node two quite small
+         * So A_250's prevlenSize shrink to 1, A_250's total size became 253(1+2+250)
+         * The prev node of node three is still node A_250.
+         * We will not shrink the node three's prevlenSize, keep it at 5 bytes */
+        zl = ziplistDelete(zl, &p);
+        ziplistRepr(zl);
+
+        p = ziplistIndex(zl, 3);
+        if (!ziplistCompare(p, (unsigned char*)"three", 5)) {
+            printf("ERROR: not \"three\"\n");
+            return 1;
+        }
+
+        /* We want to insert a node after A_250, the list became: [one two A_250 10 three 10]
+         * Because the new node is quite small, node three prevlenSize will shrink to 1 */
+        zl = ziplistInsert(zl, p, (unsigned char*)"10", 2);
+        ziplistRepr(zl);
+
+        /* Last element should equal 10 */
+        p = ziplistIndex(zl, -1);
+        if (!ziplistCompare(p, (unsigned char*)"10", 2)) {
+            printf("ERROR: not \"10\"\n");
+            return 1;
+        }
+
+        zfree(zl);
+    }
+
+    printf("ALL TESTS PASSED!\n");
+    return 0;
+}
+#endif