linux/fs/ntfs3/lib/decompress_common.h

/* 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 …

/* 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 …

static forceinline void
copy_unaligned_word(const void *src, void *dst)
{ … }


/* Generate a "word" with platform-dependent size whose bytes all contain the
 * value 'b'.
 */
static forceinline size_t repeat_byte(u8 b)
{ … }

/* 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 { … };

/* 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)
{ … }

/* 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)
{ … }

/* 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)
{ … }

/* 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)
{ … }

/* 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)
{ … }

/* Read and return the next @num_bits bits from the bitstream.  */
static forceinline u32
bitstream_read_bits(struct input_bitstream *is, u32 num_bits)
{ … }

/* Read and return the next literal byte embedded in the bitstream.  */
static forceinline u8
bitstream_read_byte(struct input_bitstream *is)
{ … }

/* Read and return the next 16-bit integer embedded in the bitstream.  */
static forceinline u16
bitstream_read_u16(struct input_bitstream *is)
{ … }

/* Read and return the next 32-bit integer embedded in the bitstream.  */
static forceinline u32
bitstream_read_u32(struct input_bitstream *is)
{ … }

/* 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)
{ … }

/* Align the input bitstream on a coding-unit boundary.  */
static forceinline void bitstream_align(struct input_bitstream *is)
{ … }

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)
{ … }

/*
 * 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)
{ … }

#endif /* _LINUX_NTFS3_LIB_DECOMPRESS_COMMON_H */