From: Ma Lin <malincns@163.com>
Date: Fri, 24 Sep 2021 11:24:29 +0000 (+0800)
Subject: Don't initialize the first parameter of _BitScanReverse* functions
X-Git-Tag: v1.5.1~1^2~76^2~3
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=95f492ea17834a6fb21013d2db0d03e0f12db025;p=thirdparty%2Fzstd.git

Don't initialize the first parameter of _BitScanReverse* functions

Like the document example, no need to initialize `r` to 0.
https://docs.microsoft.com/en-us/cpp/intrinsics/bitscanreverse-bitscanreverse64
---

diff --git a/lib/common/bitstream.h b/lib/common/bitstream.h
index 48aad7f3a..cefa1196b 100644
--- a/lib/common/bitstream.h
+++ b/lib/common/bitstream.h
@@ -145,7 +145,7 @@ MEM_STATIC unsigned BIT_highbit32 (U32 val)
 #       if STATIC_BMI2 == 1
 		return _lzcnt_u32(val) ^ 31;
 #       else
-		unsigned long r = 0;
+		unsigned long r;
 		return _BitScanReverse(&r, val) ? (unsigned)r : 0;
 #       endif
 #   elif defined(__GNUC__) && (__GNUC__ >= 3)   /* Use GCC Intrinsic */
diff --git a/lib/common/zstd_internal.h b/lib/common/zstd_internal.h
index aaf7d4665..ba1b7bbc8 100644
--- a/lib/common/zstd_internal.h
+++ b/lib/common/zstd_internal.h
@@ -358,7 +358,7 @@ MEM_STATIC U32 ZSTD_highbit32(U32 val)   /* compress, dictBuilder, decodeCorpus
 #       if STATIC_BMI2 == 1
             return _lzcnt_u32(val)^31;
 #       else
-            unsigned long r=0;
+            unsigned long r;
             return _BitScanReverse(&r, val) ? (unsigned)r : 0;
 #       endif
 #   elif defined(__GNUC__) && (__GNUC__ >= 3)   /* GCC Intrinsic */
diff --git a/lib/compress/zstd_compress_internal.h b/lib/compress/zstd_compress_internal.h
index 3dab83255..6821c9df8 100644
--- a/lib/compress/zstd_compress_internal.h
+++ b/lib/compress/zstd_compress_internal.h
@@ -708,7 +708,7 @@ static unsigned ZSTD_NbCommonBytes (size_t val)
 #           if STATIC_BMI2
 			    return _lzcnt_u64(val) >> 3;
 #           else
-			    unsigned long r = 0;
+			    unsigned long r;
 			    return _BitScanReverse64(&r, (U64)val) ? (unsigned)(r >> 3) : 0;
 #           endif
 #       elif defined(__GNUC__) && (__GNUC__ >= 4)
@@ -723,7 +723,7 @@ static unsigned ZSTD_NbCommonBytes (size_t val)
 #       endif
         } else { /* 32 bits */
 #       if defined(_MSC_VER)
-            unsigned long r = 0;
+            unsigned long r;
             return _BitScanReverse( &r, (unsigned long)val ) ? (unsigned)(r >> 3) : 0;
 #       elif defined(__GNUC__) && (__GNUC__ >= 3)
             return (__builtin_clz((U32)val) >> 3);
diff --git a/lib/dictBuilder/zdict.c b/lib/dictBuilder/zdict.c
index 9edc77fe8..2421f40f3 100644
--- a/lib/dictBuilder/zdict.c
+++ b/lib/dictBuilder/zdict.c
@@ -159,9 +159,8 @@ static unsigned ZDICT_NbCommonBytes (size_t val)
     } else {  /* Big Endian CPU */
         if (MEM_64bits()) {
 #       if defined(_MSC_VER) && defined(_WIN64)
-            unsigned long r = 0;
-            _BitScanReverse64( &r, val );
-            return (unsigned)(r>>3);
+            unsigned long r;
+            return _BitScanReverse64(&r, val) ? (unsigned)(r >> 3) : 0;
 #       elif defined(__GNUC__) && (__GNUC__ >= 3)
             return (unsigned)(__builtin_clzll(val) >> 3);
 #       else
@@ -174,9 +173,8 @@ static unsigned ZDICT_NbCommonBytes (size_t val)
 #       endif
         } else { /* 32 bits */
 #       if defined(_MSC_VER)
-            unsigned long r = 0;
-            _BitScanReverse( &r, (unsigned long)val );
-            return (unsigned)(r>>3);
+            unsigned long r;
+            return _BitScanReverse(&r, (unsigned long)val) ? (unsigned)(r >> 3) : 0;
 #       elif defined(__GNUC__) && (__GNUC__ >= 3)
             return (unsigned)(__builtin_clz((U32)val) >> 3);
 #       else
diff --git a/lib/legacy/zstd_v01.c b/lib/legacy/zstd_v01.c
index 7ab554797..6be9c8105 100644
--- a/lib/legacy/zstd_v01.c
+++ b/lib/legacy/zstd_v01.c
@@ -343,8 +343,7 @@ FORCE_INLINE unsigned FSE_highbit32 (U32 val)
 {
 #   if defined(_MSC_VER)   /* Visual */
     unsigned long r;
-    _BitScanReverse ( &r, val );
-    return (unsigned) r;
+    return _BitScanReverse(&r, val) ? (unsigned)r : 0;
 #   elif defined(__GNUC__) && (GCC_VERSION >= 304)   /* GCC Intrinsic */
     return __builtin_clz (val) ^ 31;
 #   else   /* Software version */
diff --git a/lib/legacy/zstd_v02.c b/lib/legacy/zstd_v02.c
index 89fdc7169..f26b99bc8 100644
--- a/lib/legacy/zstd_v02.c
+++ b/lib/legacy/zstd_v02.c
@@ -353,9 +353,8 @@ MEM_STATIC size_t BIT_readBitsFast(BIT_DStream_t* bitD, unsigned nbBits);
 MEM_STATIC unsigned BIT_highbit32 (U32 val)
 {
 #   if defined(_MSC_VER)   /* Visual */
-    unsigned long r=0;
-    _BitScanReverse ( &r, val );
-    return (unsigned) r;
+    unsigned long r;
+    return _BitScanReverse(&r, val) ? (unsigned)r : 0;
 #   elif defined(__GNUC__) && (__GNUC__ >= 3)   /* Use GCC Intrinsic */
     return __builtin_clz (val) ^ 31;
 #   else   /* Software version */
diff --git a/lib/legacy/zstd_v03.c b/lib/legacy/zstd_v03.c
index 5262d515a..744bde515 100644
--- a/lib/legacy/zstd_v03.c
+++ b/lib/legacy/zstd_v03.c
@@ -356,9 +356,8 @@ MEM_STATIC size_t BIT_readBitsFast(BIT_DStream_t* bitD, unsigned nbBits);
 MEM_STATIC unsigned BIT_highbit32 (U32 val)
 {
 #   if defined(_MSC_VER)   /* Visual */
-    unsigned long r=0;
-    _BitScanReverse ( &r, val );
-    return (unsigned) r;
+    unsigned long r;
+    return _BitScanReverse(&r, val) ? (unsigned)r : 0;
 #   elif defined(__GNUC__) && (__GNUC__ >= 3)   /* Use GCC Intrinsic */
     return __builtin_clz (val) ^ 31;
 #   else   /* Software version */
diff --git a/lib/legacy/zstd_v04.c b/lib/legacy/zstd_v04.c
index bee1b99dd..4d336b59f 100644
--- a/lib/legacy/zstd_v04.c
+++ b/lib/legacy/zstd_v04.c
@@ -627,9 +627,8 @@ MEM_STATIC size_t BIT_readBitsFast(BIT_DStream_t* bitD, unsigned nbBits);
 MEM_STATIC unsigned BIT_highbit32 (U32 val)
 {
 #   if defined(_MSC_VER)   /* Visual */
-    unsigned long r=0;
-    _BitScanReverse ( &r, val );
-    return (unsigned) r;
+    unsigned long r;
+    return _BitScanReverse(&r, val) ? (unsigned)r : 0;
 #   elif defined(__GNUC__) && (__GNUC__ >= 3)   /* Use GCC Intrinsic */
     return __builtin_clz (val) ^ 31;
 #   else   /* Software version */
diff --git a/lib/legacy/zstd_v05.c b/lib/legacy/zstd_v05.c
index eb8966bb4..bc293661e 100644
--- a/lib/legacy/zstd_v05.c
+++ b/lib/legacy/zstd_v05.c
@@ -756,9 +756,8 @@ MEM_STATIC size_t BITv05_readBitsFast(BITv05_DStream_t* bitD, unsigned nbBits);
 MEM_STATIC unsigned BITv05_highbit32 (U32 val)
 {
 #   if defined(_MSC_VER)   /* Visual */
-    unsigned long r=0;
-    _BitScanReverse ( &r, val );
-    return (unsigned) r;
+    unsigned long r;
+    return _BitScanReverse(&r, val) ? (unsigned)r : 0;
 #   elif defined(__GNUC__) && (__GNUC__ >= 3)   /* Use GCC Intrinsic */
     return __builtin_clz (val) ^ 31;
 #   else   /* Software version */
diff --git a/lib/legacy/zstd_v06.c b/lib/legacy/zstd_v06.c
index fcb16d4d8..7d6a35922 100644
--- a/lib/legacy/zstd_v06.c
+++ b/lib/legacy/zstd_v06.c
@@ -860,9 +860,8 @@ MEM_STATIC size_t BITv06_readBitsFast(BITv06_DStream_t* bitD, unsigned nbBits);
 MEM_STATIC unsigned BITv06_highbit32 ( U32 val)
 {
 #   if defined(_MSC_VER)   /* Visual */
-    unsigned long r=0;
-    _BitScanReverse ( &r, val );
-    return (unsigned) r;
+    unsigned long r;
+    return _BitScanReverse(&r, val) ? (unsigned)r : 0;
 #   elif defined(__GNUC__) && (__GNUC__ >= 3)   /* Use GCC Intrinsic */
     return __builtin_clz (val) ^ 31;
 #   else   /* Software version */
diff --git a/lib/legacy/zstd_v07.c b/lib/legacy/zstd_v07.c
index 0d0e46609..1449ef3ab 100644
--- a/lib/legacy/zstd_v07.c
+++ b/lib/legacy/zstd_v07.c
@@ -530,9 +530,8 @@ MEM_STATIC size_t BITv07_readBitsFast(BITv07_DStream_t* bitD, unsigned nbBits);
 MEM_STATIC unsigned BITv07_highbit32 (U32 val)
 {
 #   if defined(_MSC_VER)   /* Visual */
-    unsigned long r=0;
-    _BitScanReverse ( &r, val );
-    return (unsigned) r;
+    unsigned long r;
+    return _BitScanReverse(&r, val) ? (unsigned)r : 0;
 #   elif defined(__GNUC__) && (__GNUC__ >= 3)   /* Use GCC Intrinsic */
     return __builtin_clz (val) ^ 31;
 #   else   /* Software version */