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util: Improve bitcount.

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Sorry for not pushing this before, it got lost in stashes.
This commit is contained in:
Corbin Simpson 2009-11-28 10:13:51 -08:00
parent cad14c2542
commit c93dcbfea7
1 changed files with 8 additions and 4 deletions
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12
src/gallium/auxiliary/util/u_math.h
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@ -499,11 +499,15 @@ util_bitcount(unsigned n)
#if defined(PIPE_CC_GCC)
return __builtin_popcount(n);
#else
/* XXX there are more clever ways of doing this */
/* K&R classic bitcount.
*
* For each iteration, clear the LSB from the bitfield.
* Requires only one iteration per set bit, instead of
* one iteration per bit less than highest set bit.
*/
unsigned bits = 0;
while (n) {
bits += (n & 1);
n = n >> 1;
for (bits, n, bits++) {
n &= n - 1;
}
return bits;
#endif