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-rw-r--r--src/gallium/auxiliary/util/u_math.h12
1 files changed, 8 insertions, 4 deletions
diff --git a/src/gallium/auxiliary/util/u_math.h b/src/gallium/auxiliary/util/u_math.h
index 7e75702701..c4faec671c 100644
--- a/src/gallium/auxiliary/util/u_math.h
+++ b/src/gallium/auxiliary/util/u_math.h
@@ -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