summaryrefslogtreecommitdiffstats
path: root/fs/ntfs3/lib/decompress_common.h
diff options
context:
space:
mode:
Diffstat (limited to 'fs/ntfs3/lib/decompress_common.h')
-rw-r--r--fs/ntfs3/lib/decompress_common.h343
1 files changed, 343 insertions, 0 deletions
diff --git a/fs/ntfs3/lib/decompress_common.h b/fs/ntfs3/lib/decompress_common.h
new file mode 100644
index 000000000..dd7ced000
--- /dev/null
+++ b/fs/ntfs3/lib/decompress_common.h
@@ -0,0 +1,343 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * decompress_common.h - Code shared by the XPRESS and LZX decompressors
+ *
+ * Copyright (C) 2015 Eric Biggers
+ */
+
+#ifndef _LINUX_NTFS3_LIB_DECOMPRESS_COMMON_H
+#define _LINUX_NTFS3_LIB_DECOMPRESS_COMMON_H
+
+#include <linux/string.h>
+#include <linux/compiler.h>
+#include <linux/types.h>
+#include <linux/slab.h>
+#include <asm/unaligned.h>
+
+
+/* "Force inline" macro (not required, but helpful for performance) */
+#define forceinline __always_inline
+
+/* Enable whole-word match copying on selected architectures */
+#if defined(__i386__) || defined(__x86_64__) || defined(__ARM_FEATURE_UNALIGNED)
+# define FAST_UNALIGNED_ACCESS
+#endif
+
+/* Size of a machine word */
+#define WORDBYTES (sizeof(size_t))
+
+static forceinline void
+copy_unaligned_word(const void *src, void *dst)
+{
+ put_unaligned(get_unaligned((const size_t *)src), (size_t *)dst);
+}
+
+
+/* Generate a "word" with platform-dependent size whose bytes all contain the
+ * value 'b'.
+ */
+static forceinline size_t repeat_byte(u8 b)
+{
+ size_t v;
+
+ v = b;
+ v |= v << 8;
+ v |= v << 16;
+ v |= v << ((WORDBYTES == 8) ? 32 : 0);
+ return v;
+}
+
+/* Structure that encapsulates a block of in-memory data being interpreted as a
+ * stream of bits, optionally with interwoven literal bytes. Bits are assumed
+ * to be stored in little endian 16-bit coding units, with the bits ordered high
+ * to low.
+ */
+struct input_bitstream {
+
+ /* Bits that have been read from the input buffer. The bits are
+ * left-justified; the next bit is always bit 31.
+ */
+ u32 bitbuf;
+
+ /* Number of bits currently held in @bitbuf. */
+ u32 bitsleft;
+
+ /* Pointer to the next byte to be retrieved from the input buffer. */
+ const u8 *next;
+
+ /* Pointer to just past the end of the input buffer. */
+ const u8 *end;
+};
+
+/* Initialize a bitstream to read from the specified input buffer. */
+static forceinline void init_input_bitstream(struct input_bitstream *is,
+ const void *buffer, u32 size)
+{
+ is->bitbuf = 0;
+ is->bitsleft = 0;
+ is->next = buffer;
+ is->end = is->next + size;
+}
+
+/* Ensure the bit buffer variable for the bitstream contains at least @num_bits
+ * bits. Following this, bitstream_peek_bits() and/or bitstream_remove_bits()
+ * may be called on the bitstream to peek or remove up to @num_bits bits. Note
+ * that @num_bits must be <= 16.
+ */
+static forceinline void bitstream_ensure_bits(struct input_bitstream *is,
+ u32 num_bits)
+{
+ if (is->bitsleft < num_bits) {
+ if (is->end - is->next >= 2) {
+ is->bitbuf |= (u32)get_unaligned_le16(is->next)
+ << (16 - is->bitsleft);
+ is->next += 2;
+ }
+ is->bitsleft += 16;
+ }
+}
+
+/* Return the next @num_bits bits from the bitstream, without removing them.
+ * There must be at least @num_bits remaining in the buffer variable, from a
+ * previous call to bitstream_ensure_bits().
+ */
+static forceinline u32
+bitstream_peek_bits(const struct input_bitstream *is, const u32 num_bits)
+{
+ return (is->bitbuf >> 1) >> (sizeof(is->bitbuf) * 8 - num_bits - 1);
+}
+
+/* Remove @num_bits from the bitstream. There must be at least @num_bits
+ * remaining in the buffer variable, from a previous call to
+ * bitstream_ensure_bits().
+ */
+static forceinline void
+bitstream_remove_bits(struct input_bitstream *is, u32 num_bits)
+{
+ is->bitbuf <<= num_bits;
+ is->bitsleft -= num_bits;
+}
+
+/* Remove and return @num_bits bits from the bitstream. There must be at least
+ * @num_bits remaining in the buffer variable, from a previous call to
+ * bitstream_ensure_bits().
+ */
+static forceinline u32
+bitstream_pop_bits(struct input_bitstream *is, u32 num_bits)
+{
+ u32 bits = bitstream_peek_bits(is, num_bits);
+
+ bitstream_remove_bits(is, num_bits);
+ return bits;
+}
+
+/* Read and return the next @num_bits bits from the bitstream. */
+static forceinline u32
+bitstream_read_bits(struct input_bitstream *is, u32 num_bits)
+{
+ bitstream_ensure_bits(is, num_bits);
+ return bitstream_pop_bits(is, num_bits);
+}
+
+/* Read and return the next literal byte embedded in the bitstream. */
+static forceinline u8
+bitstream_read_byte(struct input_bitstream *is)
+{
+ if (unlikely(is->end == is->next))
+ return 0;
+ return *is->next++;
+}
+
+/* Read and return the next 16-bit integer embedded in the bitstream. */
+static forceinline u16
+bitstream_read_u16(struct input_bitstream *is)
+{
+ u16 v;
+
+ if (unlikely(is->end - is->next < 2))
+ return 0;
+ v = get_unaligned_le16(is->next);
+ is->next += 2;
+ return v;
+}
+
+/* Read and return the next 32-bit integer embedded in the bitstream. */
+static forceinline u32
+bitstream_read_u32(struct input_bitstream *is)
+{
+ u32 v;
+
+ if (unlikely(is->end - is->next < 4))
+ return 0;
+ v = get_unaligned_le32(is->next);
+ is->next += 4;
+ return v;
+}
+
+/* Read into @dst_buffer an array of literal bytes embedded in the bitstream.
+ * Return either a pointer to the byte past the last written, or NULL if the
+ * read overflows the input buffer.
+ */
+static forceinline void *bitstream_read_bytes(struct input_bitstream *is,
+ void *dst_buffer, size_t count)
+{
+ if ((size_t)(is->end - is->next) < count)
+ return NULL;
+ memcpy(dst_buffer, is->next, count);
+ is->next += count;
+ return (u8 *)dst_buffer + count;
+}
+
+/* Align the input bitstream on a coding-unit boundary. */
+static forceinline void bitstream_align(struct input_bitstream *is)
+{
+ is->bitsleft = 0;
+ is->bitbuf = 0;
+}
+
+extern int make_huffman_decode_table(u16 decode_table[], const u32 num_syms,
+ const u32 num_bits, const u8 lens[],
+ const u32 max_codeword_len,
+ u16 working_space[]);
+
+
+/* Reads and returns the next Huffman-encoded symbol from a bitstream. If the
+ * input data is exhausted, the Huffman symbol is decoded as if the missing bits
+ * are all zeroes.
+ */
+static forceinline u32 read_huffsym(struct input_bitstream *istream,
+ const u16 decode_table[],
+ u32 table_bits,
+ u32 max_codeword_len)
+{
+ u32 entry;
+ u32 key_bits;
+
+ bitstream_ensure_bits(istream, max_codeword_len);
+
+ /* Index the decode table by the next table_bits bits of the input. */
+ key_bits = bitstream_peek_bits(istream, table_bits);
+ entry = decode_table[key_bits];
+ if (entry < 0xC000) {
+ /* Fast case: The decode table directly provided the
+ * symbol and codeword length. The low 11 bits are the
+ * symbol, and the high 5 bits are the codeword length.
+ */
+ bitstream_remove_bits(istream, entry >> 11);
+ return entry & 0x7FF;
+ }
+ /* Slow case: The codeword for the symbol is longer than
+ * table_bits, so the symbol does not have an entry
+ * directly in the first (1 << table_bits) entries of the
+ * decode table. Traverse the appropriate binary tree
+ * bit-by-bit to decode the symbol.
+ */
+ bitstream_remove_bits(istream, table_bits);
+ do {
+ key_bits = (entry & 0x3FFF) + bitstream_pop_bits(istream, 1);
+ } while ((entry = decode_table[key_bits]) >= 0xC000);
+ return entry;
+}
+
+/*
+ * Copy an LZ77 match at (dst - offset) to dst.
+ *
+ * The length and offset must be already validated --- that is, (dst - offset)
+ * can't underrun the output buffer, and (dst + length) can't overrun the output
+ * buffer. Also, the length cannot be 0.
+ *
+ * @bufend points to the byte past the end of the output buffer. This function
+ * won't write any data beyond this position.
+ *
+ * Returns dst + length.
+ */
+static forceinline u8 *lz_copy(u8 *dst, u32 length, u32 offset, const u8 *bufend,
+ u32 min_length)
+{
+ const u8 *src = dst - offset;
+
+ /*
+ * Try to copy one machine word at a time. On i386 and x86_64 this is
+ * faster than copying one byte at a time, unless the data is
+ * near-random and all the matches have very short lengths. Note that
+ * since this requires unaligned memory accesses, it won't necessarily
+ * be faster on every architecture.
+ *
+ * Also note that we might copy more than the length of the match. For
+ * example, if a word is 8 bytes and the match is of length 5, then
+ * we'll simply copy 8 bytes. This is okay as long as we don't write
+ * beyond the end of the output buffer, hence the check for (bufend -
+ * end >= WORDBYTES - 1).
+ */
+#ifdef FAST_UNALIGNED_ACCESS
+ u8 * const end = dst + length;
+
+ if (bufend - end >= (ptrdiff_t)(WORDBYTES - 1)) {
+
+ if (offset >= WORDBYTES) {
+ /* The source and destination words don't overlap. */
+
+ /* To improve branch prediction, one iteration of this
+ * loop is unrolled. Most matches are short and will
+ * fail the first check. But if that check passes, then
+ * it becomes increasing likely that the match is long
+ * and we'll need to continue copying.
+ */
+
+ copy_unaligned_word(src, dst);
+ src += WORDBYTES;
+ dst += WORDBYTES;
+
+ if (dst < end) {
+ do {
+ copy_unaligned_word(src, dst);
+ src += WORDBYTES;
+ dst += WORDBYTES;
+ } while (dst < end);
+ }
+ return end;
+ } else if (offset == 1) {
+
+ /* Offset 1 matches are equivalent to run-length
+ * encoding of the previous byte. This case is common
+ * if the data contains many repeated bytes.
+ */
+ size_t v = repeat_byte(*(dst - 1));
+
+ do {
+ put_unaligned(v, (size_t *)dst);
+ src += WORDBYTES;
+ dst += WORDBYTES;
+ } while (dst < end);
+ return end;
+ }
+ /*
+ * We don't bother with special cases for other 'offset <
+ * WORDBYTES', which are usually rarer than 'offset == 1'. Extra
+ * checks will just slow things down. Actually, it's possible
+ * to handle all the 'offset < WORDBYTES' cases using the same
+ * code, but it still becomes more complicated doesn't seem any
+ * faster overall; it definitely slows down the more common
+ * 'offset == 1' case.
+ */
+ }
+#endif /* FAST_UNALIGNED_ACCESS */
+
+ /* Fall back to a bytewise copy. */
+
+ if (min_length >= 2) {
+ *dst++ = *src++;
+ length--;
+ }
+ if (min_length >= 3) {
+ *dst++ = *src++;
+ length--;
+ }
+ do {
+ *dst++ = *src++;
+ } while (--length);
+
+ return dst;
+}
+
+#endif /* _LINUX_NTFS3_LIB_DECOMPRESS_COMMON_H */