strings.h

#ifndef strings_h
#define strings_h

/* MSVC doesn't define ffs/ffsl. This dummy strings.h header is provided
 * for both */
#ifdef _MSC_VER
#  include <intrin.h>
#  pragma intrinsic(_BitScanForward)
static __forceinline int ffsl(long x) {
	unsigned long i;

	if (_BitScanForward(&i, x)) {
		return i + 1;
	}
	return 0;
}

static __forceinline int ffs(int x) {
	return ffsl(x);
}

#  ifdef  _M_X64
#    pragma intrinsic(_BitScanForward64)
#  endif

static __forceinline int ffsll(unsigned __int64 x) {
	unsigned long i;
#ifdef  _M_X64
	if (_BitScanForward64(&i, x)) {
		return i + 1;
	}
	return 0;
#else
// Fallback for 32-bit build where 64-bit version not available
// assuming little endian
	union {
		unsigned __int64 ll;
		unsigned   long l[2];
	} s;

	s.ll = x;

	if (_BitScanForward(&i, s.l[0])) {
		return i + 1;
	} else if(_BitScanForward(&i, s.l[1])) {
		return i + 33;
	}
	return 0;
#endif
}

#else
#  define ffsll(x) __builtin_ffsll(x)
#  define ffsl(x) __builtin_ffsl(x)
#  define ffs(x) __builtin_ffs(x)
#endif

#endif /* strings_h */