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| author | Michael Forney <mforney@mforney.org> | 2019-06-04 14:01:02 -0700 |
|---|---|---|
| committer | Michael Forney <mforney@mforney.org> | 2019-06-10 11:15:55 -0700 |
| commit | 9d58bbd4ffdce319128215443f7b8859f35da6b7 (patch) | |
| tree | a7dd731e5d826786e12f2051fb669cd02cc96a94 /src/utils.h | |
| parent | db7e79e78df07723dd07c8d00283244092dd8816 (diff) | |
| download | xorg-lib-libxkbcommon-9d58bbd4ffdce319128215443f7b8859f35da6b7.tar.gz | |
Use bitwise test instead of popcount to check if one bit is set
We don't need to determine the total number of bits set to determine if
exactly one is set.
Additionally, on x86_64 without any -march=* flag, __builtin_popcount
will get compiled to a function call to the compiler runtime (on gcc),
or a long sequence of bit operations (on clang).
Signed-off-by: Michael Forney <mforney@mforney.org>
Diffstat (limited to 'src/utils.h')
| -rw-r--r-- | src/utils.h | 12 |
1 files changed, 2 insertions, 10 deletions
diff --git a/src/utils.h b/src/utils.h index cb98e8e..d823e74 100644 --- a/src/utils.h +++ b/src/utils.h @@ -186,18 +186,10 @@ msb_pos(uint32_t mask) return pos; } -// Avoid conflict with other popcount()s. static inline int -my_popcount(uint32_t x) +one_bit_set(uint32_t x) { - int count; -#if defined(HAVE___BUILTIN_POPCOUNT) - count = __builtin_popcount(x); -#else - for (count = 0; x; count++) - x &= x - 1; -#endif - return count; + return x && (x & (x - 1)) == 0; } bool |