From: Nick Terrell <terrelln@fb.com>
Date: Sat, 28 Jul 2018 00:30:03 +0000 (-0700)
Subject: [FSE] Fix division by zero
X-Git-Tag: v0.0.29~53^2~2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9889bca530a2b52615eb1cd06260e9cd0c29e001;p=thirdparty%2Fzstd.git

[FSE] Fix division by zero

When the primary normalization method fails, and
`(1 << tableLog) == (maxSymbolValue + 1)`, and every symbol gets assigned
normalized weight 1 or -1 in the first loop, then the next division can
raise `SIGFPE`.
---

diff --git a/lib/compress/fse_compress.c b/lib/compress/fse_compress.c
index 07b3ab89b..95e7c1c7e 100644
--- a/lib/compress/fse_compress.c
+++ b/lib/compress/fse_compress.c
@@ -394,6 +394,9 @@ static size_t FSE_normalizeM2(short* norm, U32 tableLog, const unsigned* count,
     }
     ToDistribute = (1 << tableLog) - distributed;
 
+    if (ToDistribute == 0)
+        return 0;
+
     if ((total / ToDistribute) > lowOne) {
         /* risk of rounding to zero */
         lowOne = (U32)((total * 3) / (ToDistribute * 2));