From: Yann Collet <cyan@fb.com>
Date: Mon, 6 Nov 2017 23:42:50 +0000 (-0800)
Subject: 2-stages LZ4_count
X-Git-Tag: upstream/1.9.3~11^2~26^2~1
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=d51f0466289d9a021291e736b463cf8de7bd60bd;p=platform%2Fupstream%2Flz4.git

2-stages LZ4_count

separate first branch from the rest of the compare loop
to get dedicated prediction.

measured a 3-4% compression speed improvement.
---

diff --git a/lib/lz4.c b/lib/lz4.c
index 64a2e82..ff6496c 100644
--- a/lib/lz4.c
+++ b/lib/lz4.c
@@ -407,7 +407,15 @@ static unsigned LZ4_count(const BYTE* pIn, const BYTE* pMatch, const BYTE* pInLi
 {
     const BYTE* const pStart = pIn;
 
-    while (likely(pIn<pInLimit-(STEPSIZE-1))) {
+    if (likely(pIn < pInLimit-(STEPSIZE-1))) {
+        reg_t const diff = LZ4_read_ARCH(pMatch) ^ LZ4_read_ARCH(pIn);
+        if (!diff) {
+            pIn+=STEPSIZE; pMatch+=STEPSIZE;
+        } else {
+            return LZ4_NbCommonBytes(diff);
+    }   }
+
+    while (likely(pIn < pInLimit-(STEPSIZE-1))) {
         reg_t const diff = LZ4_read_ARCH(pMatch) ^ LZ4_read_ARCH(pIn);
         if (!diff) { pIn+=STEPSIZE; pMatch+=STEPSIZE; continue; }
         pIn += LZ4_NbCommonBytes(diff);