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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-06-15 09:41:34 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-06-15 09:41:34 +0000 |
commit | cf178685aca107aa37c748de11da01562e78c46c (patch) | |
tree | 84d60b39c1744edcbdd4dbfc5026583914432dba /src/liblzma/lz/lz_decoder.h | |
parent | Adding upstream version 5.6.1+really5.4.5. (diff) | |
download | xz-utils-cf178685aca107aa37c748de11da01562e78c46c.tar.xz xz-utils-cf178685aca107aa37c748de11da01562e78c46c.zip |
Adding upstream version 5.6.2.upstream/5.6.2upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | src/liblzma/lz/lz_decoder.h | 116 |
1 files changed, 66 insertions, 50 deletions
diff --git a/src/liblzma/lz/lz_decoder.h b/src/liblzma/lz/lz_decoder.h index ad80d4d..cb61b6e 100644 --- a/src/liblzma/lz/lz_decoder.h +++ b/src/liblzma/lz/lz_decoder.h @@ -1,3 +1,5 @@ +// SPDX-License-Identifier: 0BSD + /////////////////////////////////////////////////////////////////////////////// // /// \file lz_decoder.h @@ -6,9 +8,6 @@ // Authors: Igor Pavlov // Lasse Collin // -// This file has been put into the public domain. -// You can do whatever you want with this file. -// /////////////////////////////////////////////////////////////////////////////// #ifndef LZMA_LZ_DECODER_H @@ -17,10 +16,28 @@ #include "common.h" +/// Maximum length of a match rounded up to a nice power of 2 which is +/// a good size for aligned memcpy(). The allocated dictionary buffer will +/// be 2 * LZ_DICT_REPEAT_MAX bytes larger than the actual dictionary size: +/// +/// (1) Every time the decoder reaches the end of the dictionary buffer, +/// the last LZ_DICT_REPEAT_MAX bytes will be copied to the beginning. +/// This way dict_repeat() will only need to copy from one place, +/// never from both the end and beginning of the buffer. +/// +/// (2) The other LZ_DICT_REPEAT_MAX bytes is kept as a buffer between +/// the oldest byte still in the dictionary and the current write +/// position. This way dict_repeat(dict, dict->size - 1, &len) +/// won't need memmove() as the copying cannot overlap. +/// +/// Note that memcpy() still cannot be used if distance < len. +/// +/// LZMA's longest match length is 273 so pick a multiple of 16 above that. +#define LZ_DICT_REPEAT_MAX 288 + + typedef struct { - /// Pointer to the dictionary buffer. It can be an allocated buffer - /// internal to liblzma, or it can a be a buffer given by the - /// application when in single-call mode (not implemented yet). + /// Pointer to the dictionary buffer. uint8_t *buf; /// Write position in dictionary. The next byte will be written to @@ -35,9 +52,16 @@ typedef struct { /// Write limit size_t limit; - /// Size of the dictionary + /// Allocated size of buf. This is 2 * LZ_DICT_REPEAT_MAX bytes + /// larger than the actual dictionary size. This is enforced by + /// how the value for "full" is set; it can be at most + /// "size - 2 * LZ_DICT_REPEAT_MAX". size_t size; + /// True once the dictionary has become full and the writing position + /// has been wrapped in decode_buffer() in lz_decoder.c. + bool has_wrapped; + /// True when dictionary should be reset before decoding more data. bool need_reset; @@ -103,7 +127,16 @@ static inline uint8_t dict_get(const lzma_dict *const dict, const uint32_t distance) { return dict->buf[dict->pos - distance - 1 - + (distance < dict->pos ? 0 : dict->size)]; + + (distance < dict->pos + ? 0 : dict->size - LZ_DICT_REPEAT_MAX)]; +} + + +/// Optimized version of dict_get(dict, 0) +static inline uint8_t +dict_get0(const lzma_dict *const dict) +{ + return dict->buf[dict->pos - 1]; } @@ -132,68 +165,51 @@ dict_repeat(lzma_dict *dict, uint32_t distance, uint32_t *len) uint32_t left = my_min(dict_avail, *len); *len -= left; + size_t back = dict->pos - distance - 1; + if (distance >= dict->pos) + back += dict->size - LZ_DICT_REPEAT_MAX; + // Repeat a block of data from the history. Because memcpy() is faster // than copying byte by byte in a loop, the copying process gets split - // into three cases. + // into two cases. if (distance < left) { // Source and target areas overlap, thus we can't use // memcpy() nor even memmove() safely. do { - dict->buf[dict->pos] = dict_get(dict, distance); - ++dict->pos; + dict->buf[dict->pos++] = dict->buf[back++]; } while (--left > 0); - - } else if (distance < dict->pos) { - // The easiest and fastest case - memcpy(dict->buf + dict->pos, - dict->buf + dict->pos - distance - 1, - left); - dict->pos += left; - } else { - // The bigger the dictionary, the more rare this - // case occurs. We need to "wrap" the dict, thus - // we might need two memcpy() to copy all the data. - assert(dict->full == dict->size); - const uint32_t copy_pos - = dict->pos - distance - 1 + dict->size; - uint32_t copy_size = dict->size - copy_pos; - - if (copy_size < left) { - memmove(dict->buf + dict->pos, dict->buf + copy_pos, - copy_size); - dict->pos += copy_size; - copy_size = left - copy_size; - memcpy(dict->buf + dict->pos, dict->buf, copy_size); - dict->pos += copy_size; - } else { - memmove(dict->buf + dict->pos, dict->buf + copy_pos, - left); - dict->pos += left; - } + memcpy(dict->buf + dict->pos, dict->buf + back, left); + dict->pos += left; } // Update how full the dictionary is. - if (dict->full < dict->pos) - dict->full = dict->pos; + if (!dict->has_wrapped) + dict->full = dict->pos - 2 * LZ_DICT_REPEAT_MAX; - return unlikely(*len != 0); + return *len != 0; +} + + +static inline void +dict_put(lzma_dict *dict, uint8_t byte) +{ + dict->buf[dict->pos++] = byte; + + if (!dict->has_wrapped) + dict->full = dict->pos - 2 * LZ_DICT_REPEAT_MAX; } /// Puts one byte into the dictionary. Returns true if the dictionary was /// already full and the byte couldn't be added. static inline bool -dict_put(lzma_dict *dict, uint8_t byte) +dict_put_safe(lzma_dict *dict, uint8_t byte) { if (unlikely(dict->pos == dict->limit)) return true; - dict->buf[dict->pos++] = byte; - - if (dict->pos > dict->full) - dict->full = dict->pos; - + dict_put(dict, byte); return false; } @@ -217,8 +233,8 @@ dict_write(lzma_dict *restrict dict, const uint8_t *restrict in, *left -= lzma_bufcpy(in, in_pos, in_size, dict->buf, &dict->pos, dict->limit); - if (dict->pos > dict->full) - dict->full = dict->pos; + if (!dict->has_wrapped) + dict->full = dict->pos - 2 * LZ_DICT_REPEAT_MAX; return; } |