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lossless: Speed up ComputeCacheEntropy by 40 %

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a total impact of 1 % on encoding speed

This allows for performance neutral removal of the binary search
in cache bits selection. This will give a small improvement in
compression density.

Change-Id: If5d4d59460fa1924ce71af977320834a47c2054a
This commit is contained in:
Jyrki Alakuijala 2015-07-02 19:03:55 +00:00 committed by James Zern
parent 1ceecdc871
commit f722c8f0bd
1 changed files with 33 additions and 31 deletions
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54
src/enc/backward_references.c
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@ -828,12 +828,9 @@ static void BackwardReferences2DLocality(int xsize,
}
// Returns entropy for the given cache bits.
static double ComputeCacheEntropy(const uint32_t* const argb,
int xsize, int ysize,
static double ComputeCacheEntropy(const uint32_t* argb,
const VP8LBackwardRefs* const refs,
int cache_bits) {
int pixel_index = 0;
uint32_t k;
const int use_color_cache = (cache_bits > 0);
int cc_init = 0;
double entropy = MAX_ENTROPY;
@ -847,33 +844,40 @@ static double ComputeCacheEntropy(const uint32_t* const argb,
cc_init = VP8LColorCacheInit(&hashers, cache_bits);
if (!cc_init) goto Error;
}
if (!use_color_cache) {
while (VP8LRefsCursorOk(&c)) {
VP8LHistogramAddSinglePixOrCopy(histo, c.cur_pos);
VP8LRefsCursorNext(&c);
}
} else {
while (VP8LRefsCursorOk(&c)) {
const PixOrCopy* const v = c.cur_pos;
if (PixOrCopyIsLiteral(v)) {
if (use_color_cache &&
VP8LColorCacheContains(&hashers, argb[pixel_index])) {
// push pixel as a cache index
const int ix = VP8LColorCacheGetIndex(&hashers, argb[pixel_index]);
const PixOrCopy token = PixOrCopyCreateCacheIdx(ix);
VP8LHistogramAddSinglePixOrCopy(histo, &token);
const uint32_t pix = *argb++;
const uint32_t key = VP8LColorCacheGetIndex(&hashers, pix);
if (VP8LColorCacheLookup(&hashers, key) == pix) {
++histo->literal_[NUM_LITERAL_CODES + NUM_LENGTH_CODES + key];
} else {
VP8LHistogramAddSinglePixOrCopy(histo, v);
VP8LColorCacheSet(&hashers, key, pix);
++histo->blue_[pix & 0xff];
++histo->literal_[(pix >> 8) & 0xff];
++histo->red_[(pix >> 16) & 0xff];
++histo->alpha_[pix >> 24];
}
} else {
VP8LHistogramAddSinglePixOrCopy(histo, v);
int len = PixOrCopyLength(v);
int code, extra_bits;
VP8LPrefixEncodeBits(len, &code, &extra_bits);
++histo->literal_[NUM_LITERAL_CODES + code];
VP8LPrefixEncodeBits(PixOrCopyDistance(v), &code, &extra_bits);
++histo->distance_[code];
do {
VP8LColorCacheInsert(&hashers, *argb++);
} while(--len != 0);
}
if (use_color_cache) {
for (k = 0; k < PixOrCopyLength(v); ++k) {
VP8LColorCacheInsert(&hashers, argb[pixel_index + k]);
}
}
pixel_index += PixOrCopyLength(v);
VP8LRefsCursorNext(&c);
}
assert(pixel_index == xsize * ysize);
(void)xsize; // xsize is not used in non-debug compilations otherwise.
(void)ysize; // ysize is not used in non-debug compilations otherwise.
}
entropy = VP8LHistogramEstimateBits(histo) +
kSmallPenaltyForLargeCache * cache_bits;
Error:
@ -916,14 +920,12 @@ static int CalculateBestCacheSize(const uint32_t* const argb,
// Do a binary search to find the optimal entropy for cache_bits.
while (eval_low || eval_high) {
if (eval_low) {
entropy_low =
ComputeCacheEntropy(argb, xsize, ysize, refs, cache_bits_low);
entropy_low = ComputeCacheEntropy(argb, refs, cache_bits_low);
entropy_low += entropy_low * cache_bits_low * cost_mul;
eval_low = 0;
}
if (eval_high) {
entropy_high =
ComputeCacheEntropy(argb, xsize, ysize, refs, cache_bits_high);
entropy_high = ComputeCacheEntropy(argb, refs, cache_bits_high);
entropy_high += entropy_high * cache_bits_high * cost_mul;
eval_high = 0;
}