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Speed up BackwardReferences

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Speed up BackwardReferencesHashChainDistanceOnly method by:
1.) Remove for loop for shortmax code path.
2.) Execute the shortmax code path after regular call to
HashChainFindCopy, only if HashChainFindCopy() returns length > 2 (MIN_LENGTH).
3.) Also for shortmax, call method HashChainFindOffset (for length = 2),
instead of expensive method HashChainFindCopy().
4.) Handling first pixel (i==0) outside main loop and removing one if
condition (i > 0) per pixel.
5.) Handle the last pixel outside the main 'for' loop.

Overall compression speedup observed is around 5% (+/- noise).

Change-Id: Ifa30c4035f8d26e6e43e3c4881244d777961c22b
This commit is contained in:
Vikas Arora 2014-10-30 10:53:15 -07:00
parent abf04205b3
commit 77bdddf016
1 changed files with 88 additions and 68 deletions
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156
src/enc/backward_references.c
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@ -536,6 +536,33 @@ static WEBP_INLINE double GetDistanceCost(const CostModel* const m,
return m->distance_[code] + extra_bits;
}
static void AddSingleLiteral(const uint32_t* const argb,
VP8LHashChain* const hash_chain,
VP8LColorCache* const hashers,
const CostModel* const cost_model,
int idx, int is_last, int use_color_cache,
double prev_cost, float* const cost,
uint32_t* const dist_array) {
double cost_val = prev_cost;
const uint32_t color = argb[0];
if (!is_last) {
HashChainInsert(hash_chain, argb, idx);
}
if (use_color_cache && VP8LColorCacheContains(hashers, color)) {
const double mul0 = 0.68;
const int ix = VP8LColorCacheGetIndex(hashers, color);
cost_val += GetCacheCost(cost_model, ix) * mul0;
} else {
const double mul1 = 0.82;
if (use_color_cache) VP8LColorCacheInsert(hashers, color);
cost_val += GetLiteralCost(cost_model, color) * mul1;
}
if (cost[idx] > cost_val) {
cost[idx] = (float)cost_val;
dist_array[idx] = 1; // only one is inserted.
}
}
static int BackwardReferencesHashChainDistanceOnly(
int xsize, int ysize, const uint32_t* const argb,
int quality, int cache_bits, VP8LHashChain* const hash_chain,
@ -554,7 +581,7 @@ static int BackwardReferencesHashChainDistanceOnly(
CostModel* const cost_model =
(CostModel*)WebPSafeMalloc(1ULL, cost_model_size);
VP8LColorCache hashers;
const int min_distance_code = 2; // TODO(vikasa): tune as function of quality
const int min_distance_code = 2;
int window_size = WINDOW_SIZE;
int iter_pos = 1;
int iter_limit = -1;
@ -579,82 +606,75 @@ static int BackwardReferencesHashChainDistanceOnly(
GetParamsForHashChainFindCopy(quality, xsize, cache_bits,
&window_size, &iter_pos, &iter_limit);
HashChainInit(hash_chain);
for (i = 0; i < pix_count; ++i) {
double prev_cost = 0.0;
int shortmax;
if (i > 0) {
prev_cost = cost[i - 1];
}
for (shortmax = 0; shortmax < 2; ++shortmax) {
int offset = 0;
int len = 0;
if (i < pix_count - 1) { // FindCopy reads pixels at [i] and [i + 1].
int max_len = shortmax ? 2 : pix_count - i;
HashChainFindCopy(hash_chain, i, xsize, argb, max_len,
window_size, iter_pos, iter_limit,
&offset, &len);
// Add first pixel as literal.
AddSingleLiteral(argb + 0, hash_chain, &hashers, cost_model, 0, 0,
use_color_cache, 0.0, cost, dist_array);
for (i = 1; i < pix_count - 1; ++i) {
int offset = 0;
int len = 0;
double prev_cost = cost[i - 1];
const int max_len = pix_count - i;
HashChainFindCopy(hash_chain, i, xsize, argb, max_len, window_size,
iter_pos, iter_limit, &offset, &len);
if (len >= MIN_LENGTH) {
const int code = DistanceToPlaneCode(xsize, offset);
const double distance_cost =
prev_cost + GetDistanceCost(cost_model, code);
int k;
for (k = 1; k < len; ++k) {
const double cost_val = distance_cost + GetLengthCost(cost_model, k);
if (cost[i + k] > cost_val) {
cost[i + k] = (float)cost_val;
dist_array[i + k] = k + 1;
}
}
if (len >= MIN_LENGTH) {
const int code = DistanceToPlaneCode(xsize, offset);
const double distance_cost =
prev_cost + GetDistanceCost(cost_model, code);
int k;
for (k = 1; k < len; ++k) {
const double cost_val = distance_cost + GetLengthCost(cost_model, k);
if (cost[i + k] > cost_val) {
cost[i + k] = (float)cost_val;
dist_array[i + k] = k + 1;
// This if is for speedup only. It roughly doubles the speed, and
// makes compression worse by .1 %.
if (len >= 128 && code <= min_distance_code) {
// Long copy for short distances, let's skip the middle
// lookups for better copies.
// 1) insert the hashes.
if (use_color_cache) {
for (k = 0; k < len; ++k) {
VP8LColorCacheInsert(&hashers, argb[i + k]);
}
}
// This if is for speedup only. It roughly doubles the speed, and
// makes compression worse by .1 %.
if (len >= 128 && code <= min_distance_code) {
// Long copy for short distances, let's skip the middle
// lookups for better copies.
// 1) insert the hashes.
if (use_color_cache) {
for (k = 0; k < len; ++k) {
VP8LColorCacheInsert(&hashers, argb[i + k]);
}
// 2) Add to the hash_chain (but cannot add the last pixel)
{
const int last = (len + i < pix_count - 1) ? len + i
: pix_count - 1;
for (k = i; k < last; ++k) {
HashChainInsert(hash_chain, &argb[k], k);
}
// 2) Add to the hash_chain (but cannot add the last pixel)
{
const int last = (len + i < pix_count - 1) ? len + i
: pix_count - 1;
for (k = i; k < last; ++k) {
HashChainInsert(hash_chain, &argb[k], k);
}
}
// 3) jump.
i += len - 1; // for loop does ++i, thus -1 here.
goto next_symbol;
}
// 3) jump.
i += len - 1; // for loop does ++i, thus -1 here.
goto next_symbol;
}
if (len != MIN_LENGTH) {
int code_min_length;
double cost_total;
HashChainFindOffset(hash_chain, i, argb, MIN_LENGTH, window_size,
&offset);
code_min_length = DistanceToPlaneCode(xsize, offset);
cost_total = prev_cost +
GetDistanceCost(cost_model, code_min_length) +
GetLengthCost(cost_model, 1);
if (cost[i + 1] > cost_total) {
cost[i + 1] = (float)cost_total;
dist_array[i + 1] = 2;
}
}
}
if (i < pix_count - 1) {
HashChainInsert(hash_chain, &argb[i], i);
}
{
const double mul0 = 0.68;
const double mul1 = 0.82;
// inserting a literal pixel
double cost_val = prev_cost;
if (use_color_cache && VP8LColorCacheContains(&hashers, argb[i])) {
const int ix = VP8LColorCacheGetIndex(&hashers, argb[i]);
cost_val += GetCacheCost(cost_model, ix) * mul0;
} else {
if (use_color_cache) VP8LColorCacheInsert(&hashers, argb[i]);
cost_val += GetLiteralCost(cost_model, argb[i]) * mul1;
}
if (cost[i] > cost_val) {
cost[i] = (float)cost_val;
dist_array[i] = 1; // only one is inserted.
}
}
AddSingleLiteral(argb + i, hash_chain, &hashers, cost_model, i, 0,
use_color_cache, prev_cost, cost, dist_array);
next_symbol: ;
}
// Last pixel still to do, it can only be a single step if not reached
// through cheaper means already.
// Handle the last pixel.
if (i == (pix_count - 1)) {
AddSingleLiteral(argb + i, hash_chain, &hashers, cost_model, i, 1,
use_color_cache, cost[pix_count - 2], cost, dist_array);
}
ok = !refs->error_;
Error:
if (cc_init) VP8LColorCacheClear(&hashers);