Le 03/06/2011 01:40, Brian Paul a écrit :
> I'd like to avoid the warning if at all possible. If you replace (val
>>> 32) with (val >> (sizeof(unsigned) * 4)) does that silence it?
Yes it fix, but as Matt Turner said, it's not necessary to check this.
Btw we don't check that in the other functions.
Le 03/06/2011 06:09, Matt Turner a écrit :
> Also, if you want to check if the value is already a power-of-two,
> instead of a case statement for every POT (including 0), just do the
> standard is-power-of-two check:
>
> (x & (x - 1)) == 0
My own tests (on a Core2) shows that it's less efficient to do that, at
least with -O2 optimization enabled. With -O0, it's equal.
So here is a v2 patch with a builtin GCC optimization which is the
fastest (thx Matt to point me to this solution).
Regards.
Benjamin Bellec
diff --git a/src/gallium/auxiliary/util/u_math.h b/src/gallium/auxiliary/util/u_math.h
index 65a99fc..1b984b6 100644
--- a/src/gallium/auxiliary/util/u_math.h
+++ b/src/gallium/auxiliary/util/u_math.h
@@ -42,7 +42,6 @@
#include "pipe/p_compiler.h"
#include "util/u_debug.h"
-
#ifdef __cplusplus
extern "C" {
#endif
@@ -486,24 +485,49 @@ util_logbase2(unsigned n)
return pos;
}
-
/**
* Returns the smallest power of two >= x
*/
static INLINE unsigned
util_next_power_of_two(unsigned x)
{
- unsigned i;
-
+#if defined(PIPE_CC_GCC)
if (x == 0)
return 1;
-
- --x;
-
- for (i = 1; i < sizeof(unsigned) * 8; i <<= 1)
- x |= x >> i;
-
- return x + 1;
+ else
+ return (1 << (32 - __builtin_clz(x - 1)));
+#else
+ unsigned val = x;
+
+ switch (x)
+ {
+ case 1:
+ case 2:
+ case 4:
+ case 8:
+ case 16:
+ case 32:
+ case 64:
+ case 128:
+ case 256:
+ case 512:
+ case 1024:
+ case 2048:
+ case 4096:
+ return x; /* this is the most commonly used values */
+ case 0:
+ return 1;
+ default:
+ val--;
+ val = (val >> 1) | val;
+ val = (val >> 2) | val;
+ val = (val >> 4) | val;
+ val = (val >> 8) | val;
+ val = (val >> 16) | val;
+ val++;
+ return val;
+ }
+#endif
}
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