/* 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 */
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