/* 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 <linux/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 */
