fma 操作 字型慣例
if (PR[qp]) {
fp_check_target_register;
if (tmp_isrcode = fp_reg_disabled(f1, f2, f3, f4))
disabled_fp_register_fault(tmp_isrcode, 0);

if (fp_is_natval([f2]) || fp_is_natval(FR[f3]) || fp_is_natval(FR[f4])) {
FR[f1] = NATVAL;
fp_update_psr(f1);
} else {
tmp_default_result = fma_exception_fault_check(f2, f3, f4,
pc, sf, &tmp_fp_env);
if (fp_raise_fault(tmp_fp_env))
fp_exception_fault(fp_decode_fault(tmp_fp_env));

if (fp_is_nan_or_inf(tmp_default_result)) {
FR[f1] = tmp_default_result;
} else {
tmp_res = fp_mul(fp_reg_read(FR[f3]), fp_reg_read(FR[f4]));
if (f2 != 0)
tmp_res = fp_add(tmp_res, fp_reg_read(FR[f2]), tmp_fp_env);
FR[f1] = fp_ieee_round(tmp_res, &tmp_fp_env);
}

fp_update_fpsr(sf, tmp_fp_env);
fp_update_psr(f1);
if (fp_raise_traps(tmp_fp_env))
fp_exception_trap(fp_decode_trap(tmp_fp_env));
}
}