Count the trailing zeroes

def _op_generic_Ctz(self, args):
        """Count the trailing zeroes"""
        wtf_expr = claripy.BVV(self._from_size, self._from_size)
        for a in reversed(range(self._from_size)):
            bit = claripy.Extract(a, a, args[0])
            wtf_expr = claripy.If(bit == 1, claripy.BVV(a, self._from_size), wtf_expr)
        return wtf_expr