From 1269dc7cfb7d9799a59ae75094c02fdad3ae1eb8 Mon Sep 17 00:00:00 2001
From: hui su <huisu@google.com>
Date: Fri, 12 Aug 2016 15:16:06 -0700
Subject: [PATCH] Refactor VP8LColorCacheContains()

Return key/index if the query is found, and -1 otherwise.
The benefit of this is to save a hashing computation.

Change-Id: Iff056be330f5fb8204011259ac814f7677dd40fe
---
 src/enc/backward_references.c | 16 ++++++++++------
 src/utils/color_cache.h       |  3 ++-
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/src/enc/backward_references.c b/src/enc/backward_references.c
index fd82563a..03246389 100644
--- a/src/enc/backward_references.c
+++ b/src/enc/backward_references.c
@@ -598,9 +598,10 @@ static void AddSingleLiteralWithCostModel(const uint32_t* const argb,
                                           uint16_t* const dist_array) {
   double cost_val = prev_cost;
   const uint32_t color = argb[0];
-  if (use_color_cache && VP8LColorCacheContains(hashers, color)) {
+  const int ix = use_color_cache ? VP8LColorCacheContains(hashers, color) : -1;
+  if (ix >= 0) {
+    // use_color_cache is true and hashers contains 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;
@@ -1410,9 +1411,11 @@ static int BackwardReferencesHashChainFollowChosenPath(
       i += len;
     } else {
       PixOrCopy v;
-      if (use_color_cache && VP8LColorCacheContains(&hashers, argb[i])) {
+      const int idx =
+          use_color_cache ? VP8LColorCacheContains(&hashers, argb[i]) : -1;
+      if (idx >= 0) {
+        // use_color_cache is true and hashers contains argb[i]
         // push pixel as a color cache index
-        const int idx = VP8LColorCacheGetIndex(&hashers, argb[i]);
         v = PixOrCopyCreateCacheIdx(idx);
       } else {
         if (use_color_cache) VP8LColorCacheInsert(&hashers, argb[i]);
@@ -1601,8 +1604,9 @@ static int BackwardRefsWithLocalCache(const uint32_t* const argb,
     PixOrCopy* const v = c.cur_pos;
     if (PixOrCopyIsLiteral(v)) {
       const uint32_t argb_literal = v->argb_or_distance;
-      if (VP8LColorCacheContains(&hashers, argb_literal)) {
-        const int ix = VP8LColorCacheGetIndex(&hashers, argb_literal);
+      const int ix = VP8LColorCacheContains(&hashers, argb_literal);
+      if (ix >= 0) {
+        // hashers contains argb_literal
         *v = PixOrCopyCreateCacheIdx(ix);
       } else {
         VP8LColorCacheInsert(&hashers, argb_literal);
diff --git a/src/utils/color_cache.h b/src/utils/color_cache.h
index a9a9f642..d97fc708 100644
--- a/src/utils/color_cache.h
+++ b/src/utils/color_cache.h
@@ -53,10 +53,11 @@ static WEBP_INLINE int VP8LColorCacheGetIndex(const VP8LColorCache* const cc,
   return (kHashMul * argb) >> cc->hash_shift_;
 }
 
+// Return the key if cc contains argb, and -1 otherwise.
 static WEBP_INLINE int VP8LColorCacheContains(const VP8LColorCache* const cc,
                                               uint32_t argb) {
   const uint32_t key = (kHashMul * argb) >> cc->hash_shift_;
-  return (cc->colors_[key] == argb);
+  return (cc->colors_[key] == argb) ? (int)key : -1;
 }
 
 //------------------------------------------------------------------------------