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Diffstat (limited to 'fs/ntfs3/lib/decompress_common.h')
| -rw-r--r-- | fs/ntfs3/lib/decompress_common.h | 343 |
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 */ |