From: cyan4973 <yann.collet.73@gmail.com>
Date: Tue, 17 Jul 2018 16:52:57 +0000 (+0200)
Subject: fix #1241
X-Git-Tag: v0.0.29~51^2~8
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9597b438e931dcdd0cc8497bc330e9bcc495992a;p=thirdparty%2Fzstd.git

fix #1241

Ensure that first input position is valid for a match
even during first usage of context
by starting reference at 1
(avoiding the problematic 0).
---

diff --git a/lib/compress/zstd_compress.c b/lib/compress/zstd_compress.c
index c66862524..8f63eb953 100644
--- a/lib/compress/zstd_compress.c
+++ b/lib/compress/zstd_compress.c
@@ -1032,6 +1032,9 @@ ZSTD_reset_matchState(ZSTD_matchState_t* ms,
 
     ms->hashLog3 = hashLog3;
     memset(&ms->window, 0, sizeof(ms->window));
+    ms->window.dictLimit = 1;    /* start from 1, so that 1st position is valid */
+    ms->window.lowLimit = 1;     /* it ensures first and later CCtx usages compress the same */
+    ms->window.nextSrc = ms->window.base + 1;   /* see issue #1241 */
     ZSTD_invalidateMatchState(ms);
 
     /* opt parser space */
diff --git a/tests/fuzzer.c b/tests/fuzzer.c
index f7bacd5ca..b9d319ea2 100644
--- a/tests/fuzzer.c
+++ b/tests/fuzzer.c
@@ -411,6 +411,26 @@ static int basicUnitTests(U32 seed, double compressibility)
     }
     DISPLAYLEVEL(3, "OK \n");
 
+    DISPLAYLEVEL(3, "test%3d : re-using a CCtx should compress the same : ", testNb++);
+    {   int i;
+        for (i=0; i<20; i++)
+            ((char*)CNBuffer)[i] = i;   /* ensure no match during initial section */
+        memcpy((char*)CNBuffer + 20, CNBuffer, 10);   /* create one match, starting from beginning of sample, which is the difficult case (see #1241) */
+        for (i=1; i<=19; i++) {
+            ZSTD_CCtx* const cctx = ZSTD_createCCtx();
+            size_t size1, size2;
+            DISPLAYLEVEL(5, "l%i ", i);
+            size1 = ZSTD_compressCCtx(cctx, compressedBuffer, compressedBufferSize, CNBuffer, 30, i);
+            CHECK_Z(size1);
+            size2 = ZSTD_compressCCtx(cctx, compressedBuffer, compressedBufferSize, CNBuffer, 30, i);
+            CHECK_Z(size2);
+            CHECK_EQ(size1, size2);
+
+            ZSTD_freeCCtx(cctx);
+        }
+    }
+    DISPLAYLEVEL(3, "OK \n");
+
     DISPLAYLEVEL(3, "test%3d : ZSTD_CCtx_getParameter() : ", testNb++);
     {   ZSTD_CCtx* const cctx = ZSTD_createCCtx();
         ZSTD_outBuffer out = {NULL, 0, 0};