isl_ffs.c

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#include <isl_config.h>
 
#if !HAVE_DECL_FFS && !HAVE_DECL___BUILTIN_FFS && HAVE_DECL__BITSCANFORWARD
#include <intrin.h>
 
/* Implementation of ffs in terms of _BitScanForward.
 *
 * ffs returns the position of the least significant bit set in i,
 * with the least significant bit is position 1, or 0 if not bits are set.
 *
 * _BitScanForward returns 1 if mask is non-zero and sets index
 * to the position of the least significant bit set in i,
 * with the least significant bit is position 0.
 */
int isl_ffs(int i)
{
  unsigned char non_zero;
  unsigned long index, mask = i;
 
  non_zero = _BitScanForward(&index, mask);
 
  return non_zero ? 1 + index : 0;
}
#endif