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

if (fp_is_natval([f2]) || fp_is_natval(FR[f3])) {
FR[f1] = NATVAL;
} else {
FR[f1].significand = FR[f2].significand & ~FR[f3].significand;
FR[f1].exponent = FP_INTEGER_EXP;
FR[f1].sign = FP_SIGN_POSITIVE;
}
fp_update_psr(f1);
}