chromium/third_party/brotli/dec/bit_reader.h

/* Copyright 2013 Google Inc. All Rights Reserved.

   Distributed under MIT license.
   See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
*/

/* Bit reading helpers */

#ifndef BROTLI_DEC_BIT_READER_H_
#define BROTLI_DEC_BIT_READER_H_

#include <string.h>  /* memcpy */

#include "../common/constants.h"
#include "../common/platform.h"
#include <brotli/types.h>

#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif

#define BROTLI_SHORT_FILL_BIT_WINDOW_READ …

BROTLI_INTERNAL extern const uint32_t kBrotliBitMask[33];

static BROTLI_INLINE uint32_t BitMask(uint32_t n) { … }

BrotliBitReader;

BrotliBitReaderState;

/* Initializes the BrotliBitReader fields. */
BROTLI_INTERNAL void BrotliInitBitReader(BrotliBitReader* const br);

/* Ensures that accumulator is not empty.
   May consume up to sizeof(brotli_reg_t) - 1 bytes of input.
   Returns BROTLI_FALSE if data is required but there is no input available.
   For BROTLI_ALIGNED_READ this function also prepares bit reader for aligned
   reading. */
BROTLI_INTERNAL BROTLI_BOOL BrotliWarmupBitReader(BrotliBitReader* const br);

/* Fallback for BrotliSafeReadBits32. Extracted as noninlined method to unburden
   the main code-path. Never called for RFC brotli streams, required only for
   "large-window" mode and other extensions. */
BROTLI_INTERNAL BROTLI_NOINLINE BROTLI_BOOL BrotliSafeReadBits32Slow(
    BrotliBitReader* const br, uint32_t n_bits, uint32_t* val);

static BROTLI_INLINE void BrotliBitReaderSaveState(
    BrotliBitReader* const from, BrotliBitReaderState* to) { … }

static BROTLI_INLINE void BrotliBitReaderRestoreState(
    BrotliBitReader* const to, BrotliBitReaderState* from) { … }

static BROTLI_INLINE uint32_t BrotliGetAvailableBits(
    const BrotliBitReader* br) { … }

/* Returns amount of unread bytes the bit reader still has buffered from the
   BrotliInput, including whole bytes in br->val_. Result is capped with
   maximal ring-buffer size (larger number won't be utilized anyway). */
static BROTLI_INLINE size_t BrotliGetRemainingBytes(BrotliBitReader* br) { … }

/* Checks if there is at least |num| bytes left in the input ring-buffer
   (excluding the bits remaining in br->val_). */
static BROTLI_INLINE BROTLI_BOOL BrotliCheckInputAmount(
    BrotliBitReader* const br, size_t num) { … }

/* Guarantees that there are at least |n_bits| + 1 bits in accumulator.
   Precondition: accumulator contains at least 1 bit.
   |n_bits| should be in the range [1..24] for regular build. For portable
   non-64-bit little-endian build only 16 bits are safe to request. */
static BROTLI_INLINE void BrotliFillBitWindow(
    BrotliBitReader* const br, uint32_t n_bits) { … }

/* Mostly like BrotliFillBitWindow, but guarantees only 16 bits and reads no
   more than BROTLI_SHORT_FILL_BIT_WINDOW_READ bytes of input. */
static BROTLI_INLINE void BrotliFillBitWindow16(BrotliBitReader* const br) { … }

/* Tries to pull one byte of input to accumulator.
   Returns BROTLI_FALSE if there is no input available. */
static BROTLI_INLINE BROTLI_BOOL BrotliPullByte(BrotliBitReader* const br) { … }

/* Returns currently available bits.
   The number of valid bits could be calculated by BrotliGetAvailableBits. */
static BROTLI_INLINE brotli_reg_t BrotliGetBitsUnmasked(
    BrotliBitReader* const br) { … }

/* Like BrotliGetBits, but does not mask the result.
   The result contains at least 16 valid bits. */
static BROTLI_INLINE uint32_t BrotliGet16BitsUnmasked(
    BrotliBitReader* const br) { … }

/* Returns the specified number of bits from |br| without advancing bit
   position. */
static BROTLI_INLINE uint32_t BrotliGetBits(
    BrotliBitReader* const br, uint32_t n_bits) { … }

/* Tries to peek the specified amount of bits. Returns BROTLI_FALSE, if there
   is not enough input. */
static BROTLI_INLINE BROTLI_BOOL BrotliSafeGetBits(
    BrotliBitReader* const br, uint32_t n_bits, uint32_t* val) { … }

/* Advances the bit pos by |n_bits|. */
static BROTLI_INLINE void BrotliDropBits(
    BrotliBitReader* const br, uint32_t n_bits) { … }

static BROTLI_INLINE void BrotliBitReaderUnload(BrotliBitReader* br) { … }

/* Reads the specified number of bits from |br| and advances the bit pos.
   Precondition: accumulator MUST contain at least |n_bits|. */
static BROTLI_INLINE void BrotliTakeBits(
  BrotliBitReader* const br, uint32_t n_bits, uint32_t* val) { … }

/* Reads the specified number of bits from |br| and advances the bit pos.
   Assumes that there is enough input to perform BrotliFillBitWindow.
   Up to 24 bits are allowed to be requested from this method. */
static BROTLI_INLINE uint32_t BrotliReadBits24(
    BrotliBitReader* const br, uint32_t n_bits) { … }

/* Same as BrotliReadBits24, but allows reading up to 32 bits. */
static BROTLI_INLINE uint32_t BrotliReadBits32(
    BrotliBitReader* const br, uint32_t n_bits) { … }

/* Tries to read the specified amount of bits. Returns BROTLI_FALSE, if there
   is not enough input. |n_bits| MUST be positive.
   Up to 24 bits are allowed to be requested from this method. */
static BROTLI_INLINE BROTLI_BOOL BrotliSafeReadBits(
    BrotliBitReader* const br, uint32_t n_bits, uint32_t* val) { … }

/* Same as BrotliSafeReadBits, but allows reading up to 32 bits. */
static BROTLI_INLINE BROTLI_BOOL BrotliSafeReadBits32(
    BrotliBitReader* const br, uint32_t n_bits, uint32_t* val) { … }

/* Advances the bit reader position to the next byte boundary and verifies
   that any skipped bits are set to zero. */
static BROTLI_INLINE BROTLI_BOOL BrotliJumpToByteBoundary(BrotliBitReader* br) { … }

/* Copies remaining input bytes stored in the bit reader to the output. Value
   |num| may not be larger than BrotliGetRemainingBytes. The bit reader must be
   warmed up again after this. */
static BROTLI_INLINE void BrotliCopyBytes(uint8_t* dest,
                                          BrotliBitReader* br, size_t num) { … }

#if defined(__cplusplus) || defined(c_plusplus)
}  /* extern "C" */
#endif

#endif  /* BROTLI_DEC_BIT_READER_H_ */