From: Yann Collet <yann.collet.73@gmail.com>
Date: Mon, 19 Oct 2015 02:12:23 +0000 (+0100)
Subject: minor speed improvement
X-Git-Tag: zstd-0.2.0^2~11
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=4d1a0ef51537ff7c5296beac40b9f14a8ba51249;p=thirdparty%2Fzstd.git

minor speed improvement
---

diff --git a/lib/zstd.c b/lib/zstd.c
index 63ae947dc..4b4909f2a 100644
--- a/lib/zstd.c
+++ b/lib/zstd.c
@@ -1313,25 +1313,21 @@ static size_t ZSTD_execSequence(BYTE* op,
     static const int dec32table[] = {0, 1, 2, 1, 4, 4, 4, 4};   /* added */
     static const int dec64table[] = {8, 8, 8, 7, 8, 9,10,11};   /* substracted */
     const BYTE* const ostart = op;
-    const size_t litLength = sequence.litLength;   /* for some reason, doing the same with matchLength decreases speed ... */
-    BYTE* const oMatchEnd = op + litLength + sequence.matchLength;   /* risk : address space overflow (32-bits) */
-    const BYTE* const litEnd = *litPtr + litLength;
+    BYTE* const oLitEnd = op + sequence.litLength;
+    BYTE* const oMatchEnd = op + sequence.litLength + sequence.matchLength;   /* risk : address space overflow (32-bits) */
+    BYTE* const oend_8 = oend-8;
+    const BYTE* const litEnd = *litPtr + sequence.litLength;
 
     /* check */
+    if (oLitEnd > oend_8) return ERROR(dstSize_tooSmall);   /* last match must start at a minimum distance of 8 from oend */
     if (oMatchEnd > oend) return ERROR(dstSize_tooSmall);   /* overwrite beyond dst buffer */
-    if (litEnd > litLimit) return ERROR(corruption_detected);
+    if (litEnd > litLimit) return ERROR(corruption_detected);   /* overRead beyond lit buffer */
 
     /* copy Literals */
-    if (op+litLength > oend-8)   /* ZSTD_wildcopy() risks overwrite */
-        memmove(op, *litPtr, litLength);
-    else
-        ZSTD_wildcopy(op, *litPtr, litLength);
-    op += litLength;
+    ZSTD_wildcopy(op, *litPtr, sequence.litLength);   /* note : oLitEnd <= oend-8 : no risk of overwrite beyond oend */
+    op = oLitEnd;
     *litPtr = litEnd;   /* update for next sequence */
 
-    /* check : last match must be at a minimum distance of 8 from end of dst buffer */
-    if (oend-op < 8) return ERROR(dstSize_tooSmall);
-
     /* copy Match */
     {
         const BYTE* match = op - sequence.offset;
@@ -1356,11 +1352,11 @@ static size_t ZSTD_execSequence(BYTE* op,
 
         if (oMatchEnd > oend-12)
         {
-            if (op < oend-8)
+            if (op < oend_8)
             {
-                ZSTD_wildcopy(op, match, (oend-8) - op);
-                match += (oend-8) - op;
-                op = oend-8;
+                ZSTD_wildcopy(op, match, oend_8 - op);
+                match += oend_8 - op;
+                op = oend_8;
             }
             while (op < oMatchEnd) *op++ = *match++;
         }