Fix undefined behavior when srcSize==1

lib/common/bitstream.h

@@ -168,6 +168,8 @@ MEM_STATIC size_t BIT_readBitsFast(BIT_DStream_t* bitD, unsigned nbBits);
 *  Internal functions
 ****************************************************************/
 MEM_STATIC unsigned BIT_highbit32 (register U32 val)
+{
+    assert(val != 0);
     {
 #   if defined(_MSC_VER)   /* Visual */
         unsigned long r=0;
@@ -189,6 +191,7 @@ MEM_STATIC unsigned BIT_highbit32 (register U32 val)
         return DeBruijnClz[ (U32) (v * 0x07C4ACDDU) >> 27];
 #   endif
     }
+}
 
 /*=====    Local Constants   =====*/
 static const unsigned BIT_mask[] = { 0, 1, 3, 7, 0xF, 0x1F, 0x3F, 0x7F,

lib/common/zstd_internal.h

@@ -267,6 +267,8 @@ void ZSTD_free(void* ptr, ZSTD_customMem customMem);
 /*======  common function  ======*/
 
 MEM_STATIC U32 ZSTD_highbit32(U32 val)
+{
+    assert(val != 0);
     {
 #   if defined(_MSC_VER)   /* Visual */
         unsigned long r=0;
@@ -287,6 +289,7 @@ MEM_STATIC U32 ZSTD_highbit32(U32 val)
         return r;
 #   endif
     }
+}
 
 
 /* hidden functions */

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;