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mesa: Add a _mesa_fls() function to find the last bit set in a word.

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ffs() finds the least significant bit set; _mesa_fls() finds the /most/
significant bit.

v2: Make it an inline function in imports.h, per Brian's suggestion.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
This commit is contained in:
Kenneth Graunke 2012-09-11 22:14:58 -07:00
parent 1a5d4f7cb2
commit 0fc163408e
1 changed files with 22 additions and 0 deletions
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22
src/mesa/main/imports.h
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@ -520,6 +520,28 @@ extern unsigned int
_mesa_bitcount_64(uint64_t n);
#endif
/**
* Find the last (most significant) bit set in a word.
*
* Essentially ffs() in the reverse direction.
*/
static inline unsigned int
_mesa_fls(unsigned int n)
{
#if defined(__GNUC__) && ((__GNUC__ * 100 + __GNUC_MINOR__) >= 304)
return n == 0 ? 0 : 32 - __builtin_clz(n);
#else
unsigned int v = 1;
if (n == 0)
return 0;
while (n >>= 1)
v++;
return v;
#endif
}
extern GLhalfARB
_mesa_float_to_half(float f);