FP_RM
float_round_down = FP_RM,
float_round_down = FP_RM,
{ "RM", FP_RM, 3 },
if (rd != FP_RM) /* only -0 + -0 gives -0 */
r->fp_sign = rd == FP_RM;
case FP_RM:
case FP_RM: /* toward -Inf iff negative */