fcvt.xf Operation Font Conventions
if (PR[qp]) {
fp_check_target_register;
if (tmp_isrcode = fp_reg_disabled(f1, f2, 0, 0))
disabled_fp_register_fault(tmp_isrcode, 0);

if ( fp_is_natval([f2])) {
FR[f1] = NATVAL;
} else {
tmp_res = FR[f2];
if (tmp_res.significand{63}) {
tmp_res.significand = (~tmp_res.significand) + 1;
tmp_res.sign = 1;
} else
tmp_res.sign = 0;

tmp_res.exponent = FP_INTEGER_EXP;
tmp_res = fp_normalize(tmp_res);

FR[f1].significand = tmp_res.significand;
FR[f1].exponent = tmp_res.exponent;
FR[f1].sign = tmp_res.sign;
}
fp_update_psr(f1);
}