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Make Brotli decompression faster

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Makes it ~8% faster on my skylake desktop.

PiperOrigin-RevId: 650776651
This commit is contained in:
Ilya Tokar 2024-07-09 15:29:02 -07:00 committed by Copybara-Service
parent 39bcecf455
commit 60ffa68dec
1 changed files with 70 additions and 19 deletions
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89
c/dec/decode.c
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@ -1901,6 +1901,7 @@ static BROTLI_INLINE BROTLI_BOOL CheckInputAmount(
static BROTLI_INLINE BrotliDecoderErrorCode ProcessCommandsInternal(
int safe, BrotliDecoderState* s) {
const int kMaximalOverread = 4;
int pos = s->pos;
int i = s->loop_counter;
BrotliDecoderErrorCode result = BROTLI_DECODER_SUCCESS;
@ -1959,35 +1960,85 @@ CommandInner:
brotli_reg_t bits;
brotli_reg_t value;
PreloadSymbol(safe, s->literal_htree, br, &bits, &value);
do {
if (!CheckInputAmount(safe, br)) {
s->state = BROTLI_STATE_COMMAND_INNER;
result = BROTLI_DECODER_NEEDS_MORE_INPUT;
goto saveStateAndReturn;
if (!safe) {
// This is a hottest part of the decode, so we copy the loop below
// and optimize it by calculating the number of steps where all checks
// evaluate to false (ringbuffer size/block size/input size).
// Since all checks are loop invariant, we just need to find
// minimal number of iterations for a simple loop, and run
// the full version for the remainder.
int num_steps = i - 1;
if (num_steps > 0 && ((brotli_reg_t)(num_steps) > s->block_length[0])) {
// Safe cast, since block_length < steps
num_steps = (int)s->block_length[0];
}
if (BROTLI_PREDICT_FALSE(s->block_length[0] == 0)) {
goto NextLiteralBlock;
if (s->ringbuffer_size >= pos &&
(s->ringbuffer_size - pos) <= num_steps) {
num_steps = s->ringbuffer_size - pos - 1;
}
if (!safe) {
// Calculate range where CheckInputAmount is always true.
// We consume at most 15 bit (2 bytes) per symbol, so if we have
// x bytes, that are safe to read, with 1 iteration per symbol
// we are only guaranteed x/2 safe symbol reads. Bitreader
// also reads in brotli_reg_t sized chunks, so we over-read by
// at most 8 bytes / 2 = 4 iterations.
ptrdiff_t new_lim = (8 * (br->guard_in - br->next_in)) / 15;
if ((new_lim - kMaximalOverread) <= num_steps) {
// Safe cast, since new_lim is already < num_steps
num_steps = (int)(new_lim - kMaximalOverread);
}
if (num_steps < 0) {
num_steps = 0;
}
int pos_limit = pos + num_steps;
for (; pos < pos_limit; pos++) {
s->ringbuffer[pos] =
(uint8_t)ReadPreloadedSymbol(s->literal_htree, br, &bits, &value);
} else {
BROTLI_LOG_ARRAY_INDEX(s->ringbuffer, pos);
}
s->block_length[0] -= (brotli_reg_t)num_steps;
i -= num_steps;
do {
if (!CheckInputAmount(safe, br)) {
s->state = BROTLI_STATE_COMMAND_INNER;
result = BROTLI_DECODER_NEEDS_MORE_INPUT;
goto saveStateAndReturn;
}
if (BROTLI_PREDICT_FALSE(s->block_length[0] == 0)) {
goto NextLiteralBlock;
}
s->ringbuffer[pos] =
(uint8_t)ReadPreloadedSymbol(s->literal_htree, br, &bits, &value);
--s->block_length[0];
BROTLI_LOG_ARRAY_INDEX(s->ringbuffer, pos);
++pos;
if (BROTLI_PREDICT_FALSE(pos == s->ringbuffer_size)) {
s->state = BROTLI_STATE_COMMAND_INNER_WRITE;
--i;
goto saveStateAndReturn;
}
} while (--i != 0);
} else { /* safe */
do {
if (BROTLI_PREDICT_FALSE(s->block_length[0] == 0)) {
goto NextLiteralBlock;
}
brotli_reg_t literal;
if (!SafeReadSymbol(s->literal_htree, br, &literal)) {
result = BROTLI_DECODER_NEEDS_MORE_INPUT;
goto saveStateAndReturn;
}
s->ringbuffer[pos] = (uint8_t)literal;
}
--s->block_length[0];
BROTLI_LOG_ARRAY_INDEX(s->ringbuffer, pos);
++pos;
if (BROTLI_PREDICT_FALSE(pos == s->ringbuffer_size)) {
s->state = BROTLI_STATE_COMMAND_INNER_WRITE;
--i;
goto saveStateAndReturn;
}
} while (--i != 0);
--s->block_length[0];
BROTLI_LOG_ARRAY_INDEX(s->ringbuffer, pos);
++pos;
if (BROTLI_PREDICT_FALSE(pos == s->ringbuffer_size)) {
s->state = BROTLI_STATE_COMMAND_INNER_WRITE;
--i;
goto saveStateAndReturn;
}
} while (--i != 0);
}
} else {
uint8_t p1 = s->ringbuffer[(pos - 1) & s->ringbuffer_mask];
uint8_t p2 = s->ringbuffer[(pos - 2) & s->ringbuffer_mask];