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/* Copyright 2013 Google Inc. All Rights Reserved.
Distributed under MIT license.
*/
/* Bit reading helpers */
#ifndef BROTLI_DEC_BIT_READER_H_
#define BROTLI_DEC_BIT_READER_H_
#include <string.h> /* memcpy */
#include <brotli/types.h>
#include "../common/constants.h"
#include "../common/platform.h"
#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif
#define BROTLI_SHORT_FILL_BIT_WINDOW_READ (sizeof(brotli_reg_t) >> 1)
/* 162 bits + 7 bytes */
#define BROTLI_FAST_INPUT_SLACK 28
BROTLI_INTERNAL extern const brotli_reg_t kBrotliBitMask[33];
static BROTLI_INLINE brotli_reg_t BitMask(brotli_reg_t n) {
if (BROTLI_IS_CONSTANT(n) || BROTLI_HAS_UBFX) {
/* Masking with this expression turns to a single
"Unsigned Bit Field Extract" UBFX instruction on ARM. */
return ~(~((brotli_reg_t)0) << n);
} else {
return kBrotliBitMask[n];
}
}
typedef struct {
brotli_reg_t val_; /* pre-fetched bits */
brotli_reg_t bit_pos_; /* current bit-reading position in val_ */
const uint8_t* next_in; /* the byte we're reading from */
const uint8_t* guard_in; /* position from which "fast-path" is prohibited */
const uint8_t* last_in; /* == next_in + avail_in */
} BrotliBitReader;
typedef struct {
brotli_reg_t val_;
brotli_reg_t bit_pos_;
const uint8_t* next_in;
size_t avail_in;
} BrotliBitReaderState;
/* Initializes the BrotliBitReader fields. */
BROTLI_INTERNAL void BrotliInitBitReader(BrotliBitReader* 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_UNALIGNED_READ_FAST this function also prepares bit reader for
aligned reading. */
BROTLI_INTERNAL BROTLI_BOOL BrotliWarmupBitReader(BrotliBitReader* 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* br, brotli_reg_t n_bits, brotli_reg_t* val);
static BROTLI_INLINE size_t
BrotliBitReaderGetAvailIn(BrotliBitReader* const br) {
return (size_t)(br->last_in - br->next_in);
}
static BROTLI_INLINE void BrotliBitReaderSaveState(
BrotliBitReader* const from, BrotliBitReaderState* to) {
to->val_ = from->val_;
to->bit_pos_ = from->bit_pos_;
to->next_in = from->next_in;
to->avail_in = BrotliBitReaderGetAvailIn(from);
}
static BROTLI_INLINE void BrotliBitReaderSetInput(
BrotliBitReader* const br, const uint8_t* next_in, size_t avail_in) {
br->next_in = next_in;
br->last_in = (avail_in == 0) ? next_in : (next_in + avail_in);
if (avail_in + 1 > BROTLI_FAST_INPUT_SLACK) {
br->guard_in = next_in + (avail_in + 1 - BROTLI_FAST_INPUT_SLACK);
} else {
br->guard_in = next_in;
}
}
static BROTLI_INLINE void BrotliBitReaderRestoreState(
BrotliBitReader* const to, BrotliBitReaderState* from) {
to->val_ = from->val_;
to->bit_pos_ = from->bit_pos_;
to->next_in = from->next_in;
BrotliBitReaderSetInput(to, from->next_in, from->avail_in);
}
static BROTLI_INLINE brotli_reg_t BrotliGetAvailableBits(
const BrotliBitReader* br) {
return br->bit_pos_;
}
/* 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) {
static const size_t kCap = (size_t)1 << BROTLI_LARGE_MAX_WBITS;
size_t avail_in = BrotliBitReaderGetAvailIn(br);
if (avail_in > kCap) return kCap;
return avail_in + (BrotliGetAvailableBits(br) >> 3);
}
/* 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) {
return TO_BROTLI_BOOL(br->next_in < br->guard_in);
}
/* Load more bits into accumulator. */
static BROTLI_INLINE brotli_reg_t BrotliBitReaderLoadBits(brotli_reg_t val,
brotli_reg_t new_bits,
brotli_reg_t count,
brotli_reg_t offset) {
BROTLI_DCHECK(
!((val >> offset) & ~new_bits & ~(~((brotli_reg_t)0) << count)));
(void)count;
return val | (new_bits << offset);
}
/* 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, brotli_reg_t n_bits) {
#if (BROTLI_64_BITS)
if (BROTLI_UNALIGNED_READ_FAST && BROTLI_IS_CONSTANT(n_bits) &&
(n_bits <= 8)) {
brotli_reg_t bit_pos = br->bit_pos_;
if (bit_pos <= 8) {
br->val_ = BrotliBitReaderLoadBits(br->val_,
BROTLI_UNALIGNED_LOAD64LE(br->next_in), 56, bit_pos);
br->bit_pos_ = bit_pos + 56;
br->next_in += 7;
}
} else if (BROTLI_UNALIGNED_READ_FAST && BROTLI_IS_CONSTANT(n_bits) &&
(n_bits <= 16)) {
brotli_reg_t bit_pos = br->bit_pos_;
if (bit_pos <= 16) {
br->val_ = BrotliBitReaderLoadBits(br->val_,
BROTLI_UNALIGNED_LOAD64LE(br->next_in), 48, bit_pos);
br->bit_pos_ = bit_pos + 48;
br->next_in += 6;
}
} else {
brotli_reg_t bit_pos = br->bit_pos_;
if (bit_pos <= 32) {
br->val_ = BrotliBitReaderLoadBits(br->val_,
(uint64_t)BROTLI_UNALIGNED_LOAD32LE(br->next_in), 32, bit_pos);
br->bit_pos_ = bit_pos + 32;
br->next_in += BROTLI_SHORT_FILL_BIT_WINDOW_READ;
}
}
#else
if (BROTLI_UNALIGNED_READ_FAST && BROTLI_IS_CONSTANT(n_bits) &&
(n_bits <= 8)) {
brotli_reg_t bit_pos = br->bit_pos_;
if (bit_pos <= 8) {
br->val_ = BrotliBitReaderLoadBits(br->val_,
BROTLI_UNALIGNED_LOAD32LE(br->next_in), 24, bit_pos);
br->bit_pos_ = bit_pos + 24;
br->next_in += 3;
}
} else {
brotli_reg_t bit_pos = br->bit_pos_;
if (bit_pos <= 16) {
br->val_ = BrotliBitReaderLoadBits(br->val_,
(uint32_t)BROTLI_UNALIGNED_LOAD16LE(br->next_in), 16, bit_pos);
br->bit_pos_ = bit_pos + 16;
br->next_in += BROTLI_SHORT_FILL_BIT_WINDOW_READ;
}
}
#endif
}
/* 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) {
BrotliFillBitWindow(br, 17);
}
/* 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) {
if (br->next_in == br->last_in) {
return BROTLI_FALSE;
}
br->val_ = BrotliBitReaderLoadBits(br->val_,
(brotli_reg_t)*br->next_in, 8, br->bit_pos_);
br->bit_pos_ += 8;
++br->next_in;
return BROTLI_TRUE;
}
/* Returns currently available bits.
The number of valid bits could be calculated by BrotliGetAvailableBits. */
static BROTLI_INLINE brotli_reg_t BrotliGetBitsUnmasked(
BrotliBitReader* const br) {
return br->val_;
}
/* Like BrotliGetBits, but does not mask the result.
The result contains at least 16 valid bits. */
static BROTLI_INLINE brotli_reg_t BrotliGet16BitsUnmasked(
BrotliBitReader* const br) {
BrotliFillBitWindow(br, 16);
return (brotli_reg_t)BrotliGetBitsUnmasked(br);
}
/* Returns the specified number of bits from |br| without advancing bit
position. */
static BROTLI_INLINE brotli_reg_t BrotliGetBits(
BrotliBitReader* const br, brotli_reg_t n_bits) {
BrotliFillBitWindow(br, n_bits);
return BrotliGetBitsUnmasked(br) & BitMask(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, brotli_reg_t n_bits, brotli_reg_t* val) {
while (BrotliGetAvailableBits(br) < n_bits) {
if (!BrotliPullByte(br)) {
return BROTLI_FALSE;
}
}
*val = BrotliGetBitsUnmasked(br) & BitMask(n_bits);
return BROTLI_TRUE;
}
/* Advances the bit pos by |n_bits|. */
static BROTLI_INLINE void BrotliDropBits(
BrotliBitReader* const br, brotli_reg_t n_bits) {
br->bit_pos_ -= n_bits;
br->val_ >>= n_bits;
}
/* Make sure that there are no spectre bits in accumulator.
This is important for the cases when some bytes are skipped
(i.e. never placed into accumulator). */
static BROTLI_INLINE void BrotliBitReaderNormalize(BrotliBitReader* br) {
/* Actually, it is enough to normalize when br->bit_pos_ == 0 */
if (br->bit_pos_ < (sizeof(brotli_reg_t) << 3u)) {
br->val_ &= (((brotli_reg_t)1) << br->bit_pos_) - 1;
}
}
static BROTLI_INLINE void BrotliBitReaderUnload(BrotliBitReader* br) {
brotli_reg_t unused_bytes = BrotliGetAvailableBits(br) >> 3;
brotli_reg_t unused_bits = unused_bytes << 3;
br->next_in =
(unused_bytes == 0) ? br->next_in : (br->next_in - unused_bytes);
br->bit_pos_ -= unused_bits;
BrotliBitReaderNormalize(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,
brotli_reg_t n_bits,
brotli_reg_t* val) {
*val = BrotliGetBitsUnmasked(br) & BitMask(n_bits);
BROTLI_LOG(("[BrotliTakeBits] %d %d %d val: %6x\n",
(int)BrotliBitReaderGetAvailIn(br), (int)br->bit_pos_,
(int)n_bits, (int)*val));
BrotliDropBits(br, n_bits);
}
/* 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 brotli_reg_t BrotliReadBits24(
BrotliBitReader* const br, brotli_reg_t n_bits) {
BROTLI_DCHECK(n_bits <= 24);
if (BROTLI_64_BITS || (n_bits <= 16)) {
brotli_reg_t val;
BrotliFillBitWindow(br, n_bits);
BrotliTakeBits(br, n_bits, &val);
return val;
} else {
brotli_reg_t low_val;
brotli_reg_t high_val;
BrotliFillBitWindow(br, 16);
BrotliTakeBits(br, 16, &low_val);
BrotliFillBitWindow(br, 8);
BrotliTakeBits(br, n_bits - 16, &high_val);
return low_val | (high_val << 16);
}
}
/* Same as BrotliReadBits24, but allows reading up to 32 bits. */
static BROTLI_INLINE brotli_reg_t BrotliReadBits32(
BrotliBitReader* const br, brotli_reg_t n_bits) {
BROTLI_DCHECK(n_bits <= 32);
if (BROTLI_64_BITS || (n_bits <= 16)) {
brotli_reg_t val;
BrotliFillBitWindow(br, n_bits);
BrotliTakeBits(br, n_bits, &val);
return val;
} else {
brotli_reg_t low_val;
brotli_reg_t high_val;
BrotliFillBitWindow(br, 16);
BrotliTakeBits(br, 16, &low_val);
BrotliFillBitWindow(br, 16);
BrotliTakeBits(br, n_bits - 16, &high_val);
return low_val | (high_val << 16);
}
}
/* 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, brotli_reg_t n_bits, brotli_reg_t* val) {
BROTLI_DCHECK(n_bits <= 24);
while (BrotliGetAvailableBits(br) < n_bits) {
if (!BrotliPullByte(br)) {
return BROTLI_FALSE;
}
}
BrotliTakeBits(br, n_bits, val);
return BROTLI_TRUE;
}
/* Same as BrotliSafeReadBits, but allows reading up to 32 bits. */
static BROTLI_INLINE BROTLI_BOOL BrotliSafeReadBits32(
BrotliBitReader* const br, brotli_reg_t n_bits, brotli_reg_t* val) {
BROTLI_DCHECK(n_bits <= 32);
if (BROTLI_64_BITS || (n_bits <= 24)) {
while (BrotliGetAvailableBits(br) < n_bits) {
if (!BrotliPullByte(br)) {
return BROTLI_FALSE;
}
}
BrotliTakeBits(br, n_bits, val);
return BROTLI_TRUE;
} else {
return BrotliSafeReadBits32Slow(br, n_bits, 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) {
brotli_reg_t pad_bits_count = BrotliGetAvailableBits(br) & 0x7;
brotli_reg_t pad_bits = 0;
if (pad_bits_count != 0) {
BrotliTakeBits(br, pad_bits_count, &pad_bits);
}
BrotliBitReaderNormalize(br);
return TO_BROTLI_BOOL(pad_bits == 0);
}
static BROTLI_INLINE void BrotliDropBytes(BrotliBitReader* br, size_t num) {
/* Check detour is legal: accumulator must to be empty. */
BROTLI_DCHECK(br->bit_pos_ == 0);
BROTLI_DCHECK(br->val_ == 0);
br->next_in += num;
}
/* 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) {
while (BrotliGetAvailableBits(br) >= 8 && num > 0) {
*dest = (uint8_t)BrotliGetBitsUnmasked(br);
BrotliDropBits(br, 8);
++dest;
--num;
}
BrotliBitReaderNormalize(br);
if (num > 0) {
memcpy(dest, br->next_in, num);
BrotliDropBytes(br, num);
}
}
BROTLI_UNUSED_FUNCTION void BrotliBitReaderSuppressUnusedFunctions(void) {
BROTLI_UNUSED(&BrotliBitReaderSuppressUnusedFunctions);
BROTLI_UNUSED(&BrotliBitReaderGetAvailIn);
BROTLI_UNUSED(&BrotliBitReaderLoadBits);
BROTLI_UNUSED(&BrotliBitReaderRestoreState);
BROTLI_UNUSED(&BrotliBitReaderSaveState);
BROTLI_UNUSED(&BrotliBitReaderSetInput);
BROTLI_UNUSED(&BrotliBitReaderUnload);
BROTLI_UNUSED(&BrotliCheckInputAmount);
BROTLI_UNUSED(&BrotliCopyBytes);
BROTLI_UNUSED(&BrotliFillBitWindow16);
BROTLI_UNUSED(&BrotliGet16BitsUnmasked);
BROTLI_UNUSED(&BrotliGetBits);
BROTLI_UNUSED(&BrotliGetRemainingBytes);
BROTLI_UNUSED(&BrotliJumpToByteBoundary);
BROTLI_UNUSED(&BrotliReadBits24);
BROTLI_UNUSED(&BrotliReadBits32);
BROTLI_UNUSED(&BrotliSafeGetBits);
BROTLI_UNUSED(&BrotliSafeReadBits);
BROTLI_UNUSED(&BrotliSafeReadBits32);
}
#if defined(__cplusplus) || defined(c_plusplus)
} /* extern "C" */
#endif
#endif /* BROTLI_DEC_BIT_READER_H_ */