#define lowest_set_bit(mask) ((u_int)__builtin_ctz(mask))
#elif defined(_MSC_VER)
/*
- * Visual Studio; we support only 2005 and later, so use
+ * Visual Studio; we support only 2015 and later, so use
* _BitScanForward().
*/
#include <intrin.h>
abort(); /* mask is zero */
return (u_int)bit;
}
-#elif defined(STRINGS_H_DECLARES_FFS)
+#else
/*
- * A non-Windows OS that has <strings.h> and declares ffs() there (typically
- * UN*X conforming to a sufficiently recent version of the Single UNIX
- * Specification, but also Haiku).
+ * POSIX.1-2001 says ffs() is in <strings.h>. Every supported non-Windows OS
+ * (including Linux with musl libc and uclibc-ng) has the header and (except
+ * HP-UX) declares the function there. HP-UX declares the function in
+ * <string.h>, which has already been included.
*/
#include <strings.h>
#define lowest_set_bit(mask) ((u_int)(ffs((mask)) - 1))
-#elif defined(__hpux)
- /*
- * HP-UX 11i v3, which declares ffs() in <string.h>, which we've already
- * included. Place this branch after the <strings.h> branch, in case a later
- * release of HP-UX makes the declaration available via the standard header.
- */
- #define lowest_set_bit(mask) ((u_int)(ffs((mask)) - 1))
-#else
-/*
- * None of the above.
- * Use a perfect-hash-function-based function.
- */
-static u_int
-lowest_set_bit(int mask)
-{
- unsigned int v = (unsigned int)mask;
-
- static const u_int MultiplyDeBruijnBitPosition[32] = {
- 0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8,
- 31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9
- };
-
- /*
- * We strip off all but the lowermost set bit (v & ~v),
- * and perform a minimal perfect hash on it to look up the
- * number of low-order zero bits in a table.
- *
- * See:
- *
- * http://7ooo.mooo.com/text/ComputingTrailingZerosHOWTO.pdf
- *
- * http://supertech.csail.mit.edu/papers/debruijn.pdf
- */
- return (MultiplyDeBruijnBitPosition[((v & -v) * 0x077CB531U) >> 27]);
-}
#endif
/*