newlib-cygwin/newlib/libc/machine/w65/mulsi3.c

long
__mulsi3(unsigned long a, unsigned long b)
{
  long res = 0;
  while (a) 
    {
      if (a & 1)
	{
	  res += b;
	}
      b <<= 1;
      a >>=1;
    }
  return res;
}