cross-platform first set bit

ffs.c

#include <stdio.h>
#include <stdlib.h>

#define MVMint32 int

#ifdef __GNUC__
#define FFS(x) __builtin_ffs(x)
#elif defined(_MSC_VER)
static __inline MVMint32 FFS(MVMint32 x) {
    MVMint32 i = 0;
    if (_BitScanForward(&i, x) == 0)
        return 0;
    return i + 1;
}
#else
#error "Can't define Find First Set"
#endif

int main (int argc, char **argv) {
    int v, f;
    if (argc < 2)
        return 0;
    v = atoi(argv[1]);
    f = FFS(v);
    fprintf(stderr, "%d %d\n", v, f);
}