Use clz ^ 31 instead of 31 - clz; better codegen for GCC

diff --git a/lib/common/bitstream.h b/lib/common/bitstream.h
index 306e019cc7e184f08a3cab6ae050d53ad34bf4e0..1c294b80d13f608089278147ecd2cbf70e19f1c1 100644 (file)
--- a/lib/common/bitstream.h
+++ b/lib/common/bitstream.h
@@ -164,7 +164,7 @@ MEM_STATIC unsigned BIT_highbit32 (U32 val)
         _BitScanReverse ( &r, val );
         return (unsigned) r;
 #   elif defined(__GNUC__) && (__GNUC__ >= 3)   /* Use GCC Intrinsic */
-        return 31 - __builtin_clz (val);
+        return __builtin_clz (val) ^ 31;
 #   elif defined(__ICCARM__)    /* IAR Intrinsic */
         return 31 - __CLZ(val);
 #   else   /* Software version */

diff --git a/lib/legacy/zstd_v01.c b/lib/legacy/zstd_v01.c
index ae8cba2a3fa209eaec8514c3d9ad91c1118cc36f..8112527f058b7d82b836ca4813c7234baf50ea62 100644 (file)
--- a/lib/legacy/zstd_v01.c
+++ b/lib/legacy/zstd_v01.c
@@ -346,7 +346,7 @@ FORCE_INLINE unsigned FSE_highbit32 (U32 val)
     _BitScanReverse ( &r, val );
     return (unsigned) r;
 #   elif defined(__GNUC__) && (GCC_VERSION >= 304)   /* GCC Intrinsic */
-    return 31 - __builtin_clz (val);
+    return __builtin_clz (val) ^ 31;
 #   else   /* Software version */
     static const unsigned 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;

diff --git a/lib/legacy/zstd_v02.c b/lib/legacy/zstd_v02.c
index de0a4bd6bbeff46058a74c1c727f0a59c4e3d8e2..c8783799b9c808b667726ce51198304c3b59ba88 100644 (file)
--- a/lib/legacy/zstd_v02.c
+++ b/lib/legacy/zstd_v02.c
@@ -353,7 +353,7 @@ MEM_STATIC unsigned BIT_highbit32 (U32 val)
     _BitScanReverse ( &r, val );
     return (unsigned) r;
 #   elif defined(__GNUC__) && (__GNUC__ >= 3)   /* Use GCC Intrinsic */
-    return 31 - __builtin_clz (val);
+    return __builtin_clz (val) ^ 31;
 #   else   /* Software version */
     static const unsigned 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;

diff --git a/lib/legacy/zstd_v03.c b/lib/legacy/zstd_v03.c
index dbc83f1ee78fd3392435517688c5c6f8bcc7d18a..162bd63024d7e5b26fa7bd8b7bb8741310c80a9f 100644 (file)
--- a/lib/legacy/zstd_v03.c
+++ b/lib/legacy/zstd_v03.c
@@ -356,7 +356,7 @@ MEM_STATIC unsigned BIT_highbit32 (U32 val)
     _BitScanReverse ( &r, val );
     return (unsigned) r;
 #   elif defined(__GNUC__) && (__GNUC__ >= 3)   /* Use GCC Intrinsic */
-    return 31 - __builtin_clz (val);
+    return __builtin_clz (val) ^ 31;
 #   else   /* Software version */
     static const unsigned 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;

diff --git a/lib/legacy/zstd_v04.c b/lib/legacy/zstd_v04.c
index 201ce2b69d1b33db11dacd456176cb9e0403e5ee..4dec308168efbcf6ac5a63055b545bc6dc71ea0e 100644 (file)
--- a/lib/legacy/zstd_v04.c
+++ b/lib/legacy/zstd_v04.c
@@ -627,7 +627,7 @@ MEM_STATIC unsigned BIT_highbit32 (U32 val)
     _BitScanReverse ( &r, val );
     return (unsigned) r;
 #   elif defined(__GNUC__) && (__GNUC__ >= 3)   /* Use GCC Intrinsic */
-    return 31 - __builtin_clz (val);
+    return __builtin_clz (val) ^ 31;
 #   else   /* Software version */
     static const unsigned 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;

diff --git a/lib/legacy/zstd_v05.c b/lib/legacy/zstd_v05.c
index e347b00dcf2e611229898476a4bd3d2ff933b078..570e0ff86ee8cb4174cd0ec9d203a244efa549e9 100644 (file)
--- a/lib/legacy/zstd_v05.c
+++ b/lib/legacy/zstd_v05.c
@@ -756,7 +756,7 @@ MEM_STATIC unsigned BITv05_highbit32 (U32 val)
     _BitScanReverse ( &r, val );
     return (unsigned) r;
 #   elif defined(__GNUC__) && (__GNUC__ >= 3)   /* Use GCC Intrinsic */
-    return 31 - __builtin_clz (val);
+    return __builtin_clz (val) ^ 31;
 #   else   /* Software version */
     static const unsigned 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;

diff --git a/lib/legacy/zstd_v06.c b/lib/legacy/zstd_v06.c
index f907a3a712261a09dc0b3bfad959fb544292fec1..2a08e8dee8421e250161e49290144a6d01c726f5 100644 (file)
--- a/lib/legacy/zstd_v06.c
+++ b/lib/legacy/zstd_v06.c
@@ -860,7 +860,7 @@ MEM_STATIC unsigned BITv06_highbit32 ( U32 val)
     _BitScanReverse ( &r, val );
     return (unsigned) r;
 #   elif defined(__GNUC__) && (__GNUC__ >= 3)   /* Use GCC Intrinsic */
-    return 31 - __builtin_clz (val);
+    return __builtin_clz (val) ^ 31;
 #   else   /* Software version */
     static const unsigned 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;

diff --git a/lib/legacy/zstd_v07.c b/lib/legacy/zstd_v07.c
index a83ddc9a68b0a9d2e7bbeddc987a5582c8377298..a2eeff808e0e3df7cbc503e721901353ccb7fe2d 100644 (file)
--- a/lib/legacy/zstd_v07.c
+++ b/lib/legacy/zstd_v07.c
@@ -530,7 +530,7 @@ MEM_STATIC unsigned BITv07_highbit32 (U32 val)
     _BitScanReverse ( &r, val );
     return (unsigned) r;
 #   elif defined(__GNUC__) && (__GNUC__ >= 3)   /* Use GCC Intrinsic */
-    return 31 - __builtin_clz (val);
+    return __builtin_clz (val) ^ 31;
 #   else   /* Software version */
     static const unsigned 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;