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Optmize VP8LGetBackwardReferences LZ77 references.

Browse Source 
Use the refs_lz77 computed (with cache_bits=0) in the method 'CalculateBestCacheSize'
to regenerate the LZ77 references corresponding to the optimum cache_bits and avoid
calling costly 'BackwardReferencesLz77' one extra time.

This change leaves the compression density unchanged and speeds up compression
by 10-15%.

Change-Id: I5a92e11788d3c3f656aa7e1fba54fb5d96ee0027
This commit is contained in:
Vikas Arora 2014-11-11 11:24:02 -08:00
parent 2f0e2ba826
commit fdaac8e0ca
1 changed files with 66 additions and 10 deletions
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70
src/enc/backward_references.c
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@ -814,31 +814,84 @@ static int CalculateBestCacheSize(const uint32_t* const argb,
int xsize, int ysize, int quality,
VP8LHashChain* const hash_chain,
VP8LBackwardRefs* const refs,
int* const lz77_computed,
int* const best_cache_bits);
// Create the backward references for specified cache_bits from a source
// backward refs that is created without local color cache.
static int BackwardRefsWithLocalCache(const uint32_t* const argb,
int cache_bits,
const VP8LBackwardRefs* const refs_src,
VP8LBackwardRefs* const refs_dst) {
int pixel_index = 0;
VP8LColorCache hashers;
VP8LRefsCursor c = VP8LRefsCursorInit(refs_src);
if (!VP8LColorCacheInit(&hashers, cache_bits)) return 0;
ClearBackwardRefs(refs_dst);
while (VP8LRefsCursorOk(&c)) {
const PixOrCopy* const v_src = c.cur_pos;
if (PixOrCopyIsLiteral(v_src)) {
const uint32_t argb_literal = v_src->argb_or_distance;
if (VP8LColorCacheContains(&hashers, argb_literal)) {
const int ix = VP8LColorCacheGetIndex(&hashers, argb_literal);
BackwardRefsCursorAdd(refs_dst, PixOrCopyCreateCacheIdx(ix));
} else {
VP8LColorCacheInsert(&hashers, argb_literal);
BackwardRefsCursorAdd(refs_dst, *v_src);
}
++pixel_index;
} else {
// refs_src was created without local cache, so it can not have cache
// indexes.
int k;
assert(PixOrCopyIsCopy(v_src));
for (k = 0; k < v_src->len; ++k) {
VP8LColorCacheInsert(&hashers, argb[pixel_index++]);
}
BackwardRefsCursorAdd(refs_dst, *v_src);
}
VP8LRefsCursorNext(&c);
}
VP8LColorCacheClear(&hashers);
return 1;
}
VP8LBackwardRefs* VP8LGetBackwardReferences(
int width, int height, const uint32_t* const argb, int quality,
int* cache_bits, VP8LHashChain* const hash_chain,
VP8LBackwardRefs refs_array[2]) {
int lz77_is_useful;
int lz77_computed;
double bit_cost_lz77, bit_cost_rle;
VP8LBackwardRefs* best = NULL;
VP8LBackwardRefs* const refs_lz77 = &refs_array[0];
VP8LBackwardRefs* const refs_rle = &refs_array[1];
VP8LBackwardRefs* refs_lz77 = &refs_array[0];
VP8LBackwardRefs* refs_rle = &refs_array[1];
VP8LHistogram* histo = NULL;
if (!CalculateBestCacheSize(argb, width, height, quality, hash_chain,
refs_lz77, cache_bits)) {
refs_lz77, &lz77_computed, cache_bits)) {
goto Error;
}
// TODO(vikasa): Use the refs_lz77 computed (with cache_bits=0) in the method
// 'CalculateBestCacheSize' to regenerate the lz77 references corresponding to
// the optimum cache_bits and avoid calling 'BackwardReferencesLz77' here.
if (lz77_computed) {
// Transform refs_lz77 for the optimized cache_bits.
if (*cache_bits > 0) {
if (!BackwardRefsWithLocalCache(argb, *cache_bits, refs_lz77, refs_rle)) {
goto Error;
}
// Swap refs_lz77 and refs_rle.
best = refs_lz77;
refs_lz77 = refs_rle;
refs_rle = best;
}
} else {
if (!BackwardReferencesLz77(width, height, argb, *cache_bits, quality,
hash_chain, refs_lz77)) {
goto Error;
}
}
if (!BackwardReferencesRle(width, height, argb, *cache_bits, refs_rle)) {
goto Error;
}
@ -863,7 +916,7 @@ VP8LBackwardRefs* VP8LGetBackwardReferences(
const int try_lz77_trace_backwards = (quality >= 25);
best = refs_lz77; // default guess: lz77 is better
if (try_lz77_trace_backwards) {
VP8LBackwardRefs* const refs_trace = &refs_array[1];
VP8LBackwardRefs* const refs_trace = refs_rle;
if (!VP8LBackwardRefsCopy(refs_lz77, refs_trace)) {
best = NULL;
goto Error;
@ -955,6 +1008,7 @@ static int CalculateBestCacheSize(const uint32_t* const argb,
int xsize, int ysize, int quality,
VP8LHashChain* const hash_chain,
VP8LBackwardRefs* const refs,
int* const lz77_computed,
int* const best_cache_bits) {
int eval_low = 1;
int eval_high = 1;
@ -966,6 +1020,7 @@ static int CalculateBestCacheSize(const uint32_t* const argb,
assert(cache_bits_high <= MAX_COLOR_CACHE_BITS);
*lz77_computed = 0;
if (cache_bits_high == 0) {
*best_cache_bits = 0;
// Local color cache is disabled.
@ -1000,5 +1055,6 @@ static int CalculateBestCacheSize(const uint32_t* const argb,
if (cache_bits_high != cache_bits_low) eval_high = 1;
}
}
*lz77_computed = 1;
return 1;
}