diff options
Diffstat (limited to 'src/util/bitscan.h')
| -rw-r--r-- | src/util/bitscan.h | 17 |
1 files changed, 17 insertions, 0 deletions
diff --git a/src/util/bitscan.h b/src/util/bitscan.h index a3f2d414bd6..5cc75f0beba 100644 --- a/src/util/bitscan.h +++ b/src/util/bitscan.h @@ -38,6 +38,10 @@ #include <intrin.h> #endif +#if defined(__POPCNT__) +#include <popcntintrin.h> +#endif + #include "c99_compat.h" #ifdef __cplusplus @@ -127,7 +131,20 @@ util_is_power_of_two_or_zero(unsigned v) static inline bool util_is_power_of_two_nonzero(unsigned v) { + /* __POPCNT__ is different from HAVE___BUILTIN_POPCOUNT. The latter + * indicates the existence of the __builtin_popcount function. The former + * indicates that _mm_popcnt_u32 exists and is a native instruction. + * + * The other alternative is to use SSE 4.2 compile-time flags. This has + * two drawbacks. First, there is currently no build infrastructure for + * SSE 4.2 (only 4.1), so that would have to be added. Second, some AMD + * CPUs support POPCNT but not SSE 4.2 (e.g., Barcelona). + */ +#ifdef __POPCNT__ + return _mm_popcnt_u32(v) == 1; +#else return v != 0 && (v & (v - 1)) == 0; +#endif } /* For looping over a bitmask when you want to loop over consecutive bits |