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0.5-2.9% decoder speedup
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PiperOrigin-RevId: 529412095
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@eustas
eustas committed Jul 4, 2023
1 parent 11abde4 commit e252f1f
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Showing 2 changed files with 48 additions and 40 deletions.
3 changes: 2 additions & 1 deletion c/dec/bit_reader.c
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Original file line number Diff line number Diff line change
Expand Up @@ -29,7 +29,7 @@ const brotli_reg_t kBrotliBitMask[33] = { 0x00000000,

void BrotliInitBitReader(BrotliBitReader* const br) {
br->val_ = 0;
br->bit_pos_ = sizeof(br->val_) << 3;
br->bit_pos_ = 0;
}

BROTLI_BOOL BrotliWarmupBitReader(BrotliBitReader* const br) {
Expand All @@ -41,6 +41,7 @@ BROTLI_BOOL BrotliWarmupBitReader(BrotliBitReader* const br) {
aligned_read_mask = 0;
}
if (BrotliGetAvailableBits(br) == 0) {
br->val_ = 0;
if (!BrotliPullByte(br)) {
return BROTLI_FALSE;
}
Expand Down
85 changes: 46 additions & 39 deletions c/dec/bit_reader.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -102,7 +102,7 @@ static BROTLI_INLINE void BrotliBitReaderRestoreState(

static BROTLI_INLINE brotli_reg_t BrotliGetAvailableBits(
const BrotliBitReader* br) {
return (BROTLI_64_BITS ? 64 : 32) - br->bit_pos_;
return br->bit_pos_;
}

/* Returns amount of unread bytes the bit reader still has buffered from the
Expand All @@ -122,6 +122,17 @@ static BROTLI_INLINE BROTLI_BOOL BrotliCheckInputAmount(
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
Expand All @@ -132,51 +143,46 @@ static BROTLI_INLINE void BrotliFillBitWindow(
if (BROTLI_UNALIGNED_READ_FAST && BROTLI_IS_CONSTANT(n_bits) &&
(n_bits <= 8)) {
brotli_reg_t bit_pos = br->bit_pos_;
if (bit_pos >= 56) {
br->val_ =
(br->val_ >> 56) | (BROTLI_UNALIGNED_LOAD64LE(br->next_in) << 8);
br->bit_pos_ =
bit_pos ^ 56; /* here same as -= 56 because of the if condition */
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 >= 48) {
br->val_ =
(br->val_ >> 48) | (BROTLI_UNALIGNED_LOAD64LE(br->next_in) << 16);
br->bit_pos_ =
bit_pos ^ 48; /* here same as -= 48 because of the if condition */
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_ = (br->val_ >> 32) |
(((uint64_t)BROTLI_UNALIGNED_LOAD32LE(br->next_in)) << 32);
br->bit_pos_ =
bit_pos ^ 32; /* here same as -= 32 because of the if condition */
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 >= 24) {
br->val_ =
(br->val_ >> 24) | (BROTLI_UNALIGNED_LOAD32LE(br->next_in) << 8);
br->bit_pos_ =
bit_pos ^ 24; /* here same as -= 24 because of the if condition */
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_ = (br->val_ >> 16) |
(((brotli_reg_t)BROTLI_UNALIGNED_LOAD16LE(br->next_in)) << 16);
br->bit_pos_ =
bit_pos ^ 16; /* here same as -= 16 because of the if condition */
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;
}
}
Expand All @@ -195,13 +201,9 @@ static BROTLI_INLINE BROTLI_BOOL BrotliPullByte(BrotliBitReader* const br) {
if (br->next_in == br->last_in) {
return BROTLI_FALSE;
}
br->val_ >>= 8;
#if (BROTLI_64_BITS)
br->val_ |= ((uint64_t)*br->next_in) << 56;
#else
br->val_ |= ((brotli_reg_t)*br->next_in) << 24;
#endif
br->bit_pos_ -= 8;
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;
}
Expand All @@ -210,7 +212,7 @@ static BROTLI_INLINE BROTLI_BOOL BrotliPullByte(BrotliBitReader* const br) {
The number of valid bits could be calculated by BrotliGetAvailableBits. */
static BROTLI_INLINE brotli_reg_t BrotliGetBitsUnmasked(
BrotliBitReader* const br) {
return br->val_ >> br->bit_pos_;
return br->val_;
}

/* Like BrotliGetBits, but does not mask the result.
Expand Down Expand Up @@ -245,20 +247,20 @@ static BROTLI_INLINE BROTLI_BOOL BrotliSafeGetBits(
/* 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->bit_pos_ -= n_bits;
br->val_ >>= n_bits;
}

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);
if (unused_bits == sizeof(br->val_) << 3) {
br->bit_pos_ -= unused_bits;
/* Prepare for possible input discontinuity. */
if (br->bit_pos_ == 0) {
br->val_ = 0;
} else {
br->val_ <<= unused_bits;
}
br->bit_pos_ += unused_bits;
}

/* Reads the specified number of bits from |br| and advances the bit pos.
Expand Down Expand Up @@ -373,6 +375,10 @@ static BROTLI_INLINE void BrotliCopyBytes(uint8_t* dest,
++dest;
--num;
}
/* Prepare for possible input discontinuity. */
if (br->bit_pos_ == 0) {
br->val_ = 0;
}
if (num > 0) {
memcpy(dest, br->next_in, num);
BrotliDropBytes(br, num);
Expand All @@ -383,6 +389,7 @@ BROTLI_UNUSED_FUNCTION void BrotliBitReaderSuppressUnusedFunctions(void) {
BROTLI_UNUSED(&BrotliBitReaderSuppressUnusedFunctions);

BROTLI_UNUSED(&BrotliBitReaderGetAvailIn);
BROTLI_UNUSED(&BrotliBitReaderLoadBits);
BROTLI_UNUSED(&BrotliBitReaderRestoreState);
BROTLI_UNUSED(&BrotliBitReaderSaveState);
BROTLI_UNUSED(&BrotliBitReaderSetInput);
Expand Down

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