Home | History | Annotate | Line # | Download | only in dist 
      1 #include <isl_config.h>
      2 
      3 #if !HAVE_DECL_FFS && !HAVE_DECL___BUILTIN_FFS && HAVE_DECL__BITSCANFORWARD
      4 #include <intrin.h>
      5 
      6 /* Implementation of ffs in terms of _BitScanForward.
      7  *
      8  * ffs returns the position of the least significant bit set in i,
      9  * with the least significant bit is position 1, or 0 if not bits are set.
     10  *
     11  * _BitScanForward returns 1 if mask is non-zero and sets index
     12  * to the position of the least significant bit set in i,
     13  * with the least significant bit is position 0.
     14  */
     15 int isl_ffs(int i)
     16 {
     17 	unsigned char non_zero;
     18 	unsigned long index, mask = i;
     19 
     20 	non_zero = _BitScanForward(&index, mask);
     21 
     22 	return non_zero ? 1 + index : 0;
     23 }
     24 #endif
     25