From d3a13397d921d9d2ebae56d0503d23c73fee39b1 Mon Sep 17 00:00:00 2001
From: Yann Collet <cyan@fb.com>
Date: Sun, 11 Feb 2018 21:03:39 -0800
Subject: slight hc speed benefit (~+1%)

by optimizing countback
---
 lib/lz4hc.c | 31 ++++++++++---------------------
 1 file changed, 10 insertions(+), 21 deletions(-)

diff --git a/lib/lz4hc.c b/lib/lz4hc.c
index 9f59e80..c888ee1 100644
--- a/lib/lz4hc.c
+++ b/lib/lz4hc.c
@@ -123,10 +123,12 @@ LZ4_FORCE_INLINE
 int LZ4HC_countBack(const BYTE* const ip, const BYTE* const match,
                     const BYTE* const iMin, const BYTE* const mMin)
 {
-    int back=0;
-    while ( (ip+back > iMin)
-         && (match+back > mMin)
-         && (ip[back-1] == match[back-1]))
+    int back = 0;
+    int const min = (int)MAX(iMin - ip, mMin - match);
+    assert(ip >= iMin); assert((size_t)(ip-iMin) < (1U<<31));
+    assert(match >= mMin); assert((size_t)(match - mMin) < (1U<<31));
+    while ( (back > min)
+         && (ip[back-1] == match[back-1]) )
             back--;
     return back;
 }
@@ -223,17 +225,7 @@ LZ4_FORCE_INLINE int LZ4HC_InsertAndGetWiderMatch (
             if (LZ4_read16(iLowLimit + longest - 1) == LZ4_read16(matchPtr - delta + longest - 1)) {
                 if (LZ4_read32(matchPtr) == pattern) {
                     int mlt = MINMATCH + LZ4_count(ip+MINMATCH, matchPtr+MINMATCH, iHighLimit);
-    #if 0
-                    /* more generic but unfortunately slower on clang */
-                    int const back = LZ4HC_countBack(ip, matchPtr, iLowLimit, lowPrefixPtr);
-    #else
-                    int back = 0;
-                    while ( (ip+back > iLowLimit)
-                         && (matchPtr+back > lowPrefixPtr)
-                         && (ip[back-1] == matchPtr[back-1])) {
-                            back--;
-                    }
-    #endif
+                    int const back = delta ? LZ4HC_countBack(ip, matchPtr, iLowLimit, lowPrefixPtr) : 0;
                     mlt -= back;
 
                     if (mlt > longest) {
@@ -252,10 +244,7 @@ LZ4_FORCE_INLINE int LZ4HC_InsertAndGetWiderMatch (
                 mlt = LZ4_count(ip+MINMATCH, matchPtr+MINMATCH, vLimit) + MINMATCH;
                 if ((ip+mlt == vLimit) && (vLimit < iHighLimit))
                     mlt += LZ4_count(ip+mlt, base+dictLimit, iHighLimit);
-                while ( (ip+back > iLowLimit)
-                     && (matchIndex+back > lowLimit)
-                     && (ip[back-1] == matchPtr[back-1]))
-                        back--;
+                back = delta ? LZ4HC_countBack(ip, matchPtr, iLowLimit, dictBase+lowLimit) : 0;
                 mlt -= back;
                 if (mlt > longest) {
                     longest = mlt;
@@ -333,7 +322,7 @@ LZ4_FORCE_INLINE int LZ4HC_encodeSequence (
     size_t length;
     BYTE* const token = (*op)++;
 
-#if defined(LZ4_DEBUG) && (LZ4_DEBUG >= 2)
+#if defined(LZ4_DEBUG) && (LZ4_DEBUG >= 6)
     static const BYTE* start = NULL;
     static U32 totalCost = 0;
     U32 const pos = (start==NULL) ? 0 : (U32)(*anchor - start);
@@ -343,7 +332,7 @@ LZ4_FORCE_INLINE int LZ4HC_encodeSequence (
     U32 const cost = 1 + llAdd + ll + 2 + mlAdd;
     if (start==NULL) start = *anchor;  /* only works for single segment */
     //g_debuglog_enable = (pos >= 2228) & (pos <= 2262);
-    DEBUGLOG(2, "pos:%7u -- literals:%3u, match:%4i, offset:%5u, cost:%3u + %u",
+    DEBUGLOG(6, "pos:%7u -- literals:%3u, match:%4i, offset:%5u, cost:%3u + %u",
                 pos,
                 (U32)(*ip - *anchor), matchLength, (U32)(*ip-match),
                 cost, totalCost);
-- 
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