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authorPauli Nieminen <suokkos@gmail.com>2010-02-14 14:16:20 +0200
committerPauli Nieminen <suokkos@gmail.com>2010-02-14 19:55:58 +0200
commit6e958832afe9544973528bed78dd3a340b8686f3 (patch)
treea4e63d1468fc8854649bfc3afc33d04eb4b36fc4
parent7344e20ce4a333bfd8ab142cfdf98098e16b001d (diff)
mesa: Don't pass paramter to __builtin_clz which would hve undefined result.
__builtin_clz with parameter 0 has undefined value. When using -O3 optimizing this would result to too large next power of two value. Fix is to check if passed value is 1 and modify formula for that case.
-rw-r--r--src/mesa/main/imports.h16
1 files changed, 11 insertions, 5 deletions
diff --git a/src/mesa/main/imports.h b/src/mesa/main/imports.h
index 3843f50036c..e3d2ac9b427 100644
--- a/src/mesa/main/imports.h
+++ b/src/mesa/main/imports.h
@@ -412,13 +412,19 @@ _mesa_is_pow_two(int x)
* Source for the fallback implementation is
* Sean Eron Anderson's webpage "Bit Twiddling Hacks"
* http://graphics.stanford.edu/~seander/bithacks.html
+ *
+ * When using builtin function have to do some work
+ * for case when passed values 1 to prevent hiting
+ * undefined result from __builtin_clz. Undefined
+ * results would be different depending on optimization
+ * level used for build.
*/
static INLINE int32_t
_mesa_next_pow_two_32(uint32_t x)
{
#ifdef __GNUC__
- x--;
- return 1 << ((__builtin_clz(x) ^ 31) + 1);
+ uint32_t y = (x != 1);
+ return (1 + y) << ((__builtin_clz(x - y) ^ 31) );
#else
x--;
x |= x >> 1;
@@ -435,11 +441,11 @@ static INLINE int64_t
_mesa_next_pow_two_64(uint64_t x)
{
#ifdef __GNUC__
- x--;
+ uint64_t y = (x != 1);
if (sizeof(x) == sizeof(long))
- return 1 << ((__builtin_clzl(x) ^ 63) + 1);
+ return (1 + y) << ((__builtin_clzl(x - y) ^ 63));
else
- return 1 << ((__builtin_clzll(x) ^ 63) + 1);
+ return (1 + y) << ((__builtin_clzll(x - y) ^ 63));
#else
x--;
x |= x >> 1;