Merge pull request #813 from stellamplau/highbit32fix

Fix undefined behavior when srcSize==1

lib/common/bitstream.h

@@ -169,25 +169,28 @@ MEM_STATIC size_t BIT_readBitsFast(BIT_DStream_t* bitD, unsigned nbBits);
 ****************************************************************/
 MEM_STATIC unsigned BIT_highbit32 (register U32 val)
 {
+    assert(val != 0);
+    {
 #   if defined(_MSC_VER)   /* Visual */
-    unsigned long r=0;
+        unsigned long r=0;
-    _BitScanReverse ( &r, val );
+        _BitScanReverse ( &r, val );
-    return (unsigned) r;
+        return (unsigned) r;
 #   elif defined(__GNUC__) && (__GNUC__ >= 3)   /* Use GCC Intrinsic */
-    return 31 - __builtin_clz (val);
+        return 31 - __builtin_clz (val);
 #   else   /* Software version */
-    static const unsigned DeBruijnClz[32] = { 0,  9,  1, 10, 13, 21,  2, 29,
+        static const unsigned DeBruijnClz[32] = { 0,  9,  1, 10, 13, 21,  2, 29,
-                                             11, 14, 16, 18, 22, 25,  3, 30,
+                                                 11, 14, 16, 18, 22, 25,  3, 30,
-                                              8, 12, 20, 28, 15, 17, 24,  7,
+                                                  8, 12, 20, 28, 15, 17, 24,  7,
-                                             19, 27, 23,  6, 26,  5,  4, 31 };
+                                                 19, 27, 23,  6, 26,  5,  4, 31 };
-    U32 v = val;
+        U32 v = val;
-    v |= v >> 1;
+        v |= v >> 1;
-    v |= v >> 2;
+        v |= v >> 2;
-    v |= v >> 4;
+        v |= v >> 4;
-    v |= v >> 8;
+        v |= v >> 8;
-    v |= v >> 16;
+        v |= v >> 16;
-    return DeBruijnClz[ (U32) (v * 0x07C4ACDDU) >> 27];
+        return DeBruijnClz[ (U32) (v * 0x07C4ACDDU) >> 27];
 #   endif
+    }
 }
 
 /*=====    Local Constants   =====*/

lib/common/zstd_internal.h

@@ -268,24 +268,27 @@ void ZSTD_free(void* ptr, ZSTD_customMem customMem);
 
 MEM_STATIC U32 ZSTD_highbit32(U32 val)
 {
+    assert(val != 0);
+    {
 #   if defined(_MSC_VER)   /* Visual */
-    unsigned long r=0;
+        unsigned long r=0;
-    _BitScanReverse(&r, val);
+        _BitScanReverse(&r, val);
-    return (unsigned)r;
+        return (unsigned)r;
 #   elif defined(__GNUC__) && (__GNUC__ >= 3)   /* GCC Intrinsic */
-    return 31 - __builtin_clz(val);
+        return 31 - __builtin_clz(val);
 #   else   /* Software version */
-    static const int DeBruijnClz[32] = { 0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30, 8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31 };
+        static const int DeBruijnClz[32] = { 0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30, 8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31 };
-    U32 v = val;
+        U32 v = val;
-    int r;
+        int r;
-    v |= v >> 1;
+        v |= v >> 1;
-    v |= v >> 2;
+        v |= v >> 2;
-    v |= v >> 4;
+        v |= v >> 4;
-    v |= v >> 8;
+        v |= v >> 8;
-    v |= v >> 16;
+        v |= v >> 16;
-    r = DeBruijnClz[(U32)(v * 0x07C4ACDDU) >> 27];
+        r = DeBruijnClz[(U32)(v * 0x07C4ACDDU) >> 27];
-    return r;
+        return r;
 #   endif
+    }
 }
 
 

lib/compress/zstd_compress.c

@@ -497,7 +497,8 @@ ZSTD_compressionParameters ZSTD_adjustCParams_internal(ZSTD_compressionParameter
     {   U32 const minSrcSize = (srcSize==0) ? 500 : 0;
         U64 const rSize = srcSize + dictSize + minSrcSize;
         if (rSize < ((U64)1<<ZSTD_WINDOWLOG_MAX)) {
-            U32 const srcLog = MAX(ZSTD_HASHLOG_MIN, ZSTD_highbit32((U32)(rSize)-1) + 1);
+            U32 const srcLog =
+                    MAX(ZSTD_HASHLOG_MIN, (rSize==1) ? 1 : ZSTD_highbit32((U32)(rSize)-1) + 1);
             if (cPar.windowLog > srcLog) cPar.windowLog = srcLog;
     }   }
     if (cPar.hashLog > cPar.windowLog) cPar.hashLog = cPar.windowLog;