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Compute the hash chain once and for all for lossless compression.

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In some cases, the hash chain for a function is filled several
times:
- GetBackwardReferences -> CalculateBestCacheSize ->
BackwardReferencesLz77 that computes the hash chain
- GetBackwardReferences ->
(not always) BackwardReferencesTraceBackwards ->
BackwardReferencesHashChainDistanceOnly that computes the hash
chain in a slightly different way

Speed and compression performance are slightly changed (+ or -)
but will be homogneized in a later patch.

Change-Id: I43f0ecc7a9312c2ed6cdba1c0fabc6c5ad91c953
This commit is contained in:
Vincent Rabaud
2016-05-24 18:00:48 +02:00
parent eee788e26a
commit d963775859
3 changed files with 71 additions and 91 deletions
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9
src/enc/backward_references.h
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@ -115,8 +115,6 @@ static WEBP_INLINE uint32_t PixOrCopyDistance(const PixOrCopy* const p) {
typedef struct VP8LHashChain VP8LHashChain;
struct VP8LHashChain {
// Stores the most recently added position with the given hash value.
int32_t hash_to_first_index_[HASH_SIZE];
// chain_[pos] stores the previous position with the same hash value
// for every pixel in the image.
int32_t* chain_;
@ -127,6 +125,9 @@ struct VP8LHashChain {
// Must be called first, to set size.
int VP8LHashChainInit(VP8LHashChain* const p, int size);
// Pre-compute the best matches for argb.
int VP8LHashChainFill(VP8LHashChain* const p,
const uint32_t* const argb, int xsize, int ysize);
void VP8LHashChainClear(VP8LHashChain* const p); // release memory
// -----------------------------------------------------------------------------
@ -192,8 +193,8 @@ static WEBP_INLINE void VP8LRefsCursorNext(VP8LRefsCursor* const c) {
// refs[0] or refs[1].
VP8LBackwardRefs* VP8LGetBackwardReferences(
int width, int height, const uint32_t* const argb, int quality,
int low_effort, int* const cache_bits, VP8LHashChain* const hash_chain,
VP8LBackwardRefs refs[2]);
int low_effort, int* const cache_bits,
const VP8LHashChain* const hash_chain, VP8LBackwardRefs refs[2]);
#ifdef __cplusplus
}