in math-emu/fpu_trig.c [784:1023]
static void do_fprem(FPU_REG *st0_ptr, u_char st0_tag, int round)
{
FPU_REG *st1_ptr = &st(1);
u_char st1_tag = FPU_gettagi(1);
if (!((st0_tag ^ TAG_Valid) | (st1_tag ^ TAG_Valid))) {
FPU_REG tmp, st0, st1;
u_char st0_sign, st1_sign;
u_char tmptag;
int tag;
int old_cw;
int expdif;
long long q;
unsigned short saved_status;
int cc;
fprem_valid:
/* Convert registers for internal use. */
st0_sign = FPU_to_exp16(st0_ptr, &st0);
st1_sign = FPU_to_exp16(st1_ptr, &st1);
expdif = exponent16(&st0) - exponent16(&st1);
old_cw = control_word;
cc = 0;
/* We want the status following the denorm tests, but don't want
the status changed by the arithmetic operations. */
saved_status = partial_status;
control_word &= ~CW_RC;
control_word |= RC_CHOP;
if (expdif < 64) {
/* This should be the most common case */
if (expdif > -2) {
u_char sign = st0_sign ^ st1_sign;
tag = FPU_u_div(&st0, &st1, &tmp,
PR_64_BITS | RC_CHOP | 0x3f,
sign);
setsign(&tmp, sign);
if (exponent(&tmp) >= 0) {
FPU_round_to_int(&tmp, tag); /* Fortunately, this can't
overflow to 2^64 */
q = significand(&tmp);
rem_kernel(significand(&st0),
&significand(&tmp),
significand(&st1),
q, expdif);
setexponent16(&tmp, exponent16(&st1));
} else {
reg_copy(&st0, &tmp);
q = 0;
}
if ((round == RC_RND)
&& (tmp.sigh & 0xc0000000)) {
/* We may need to subtract st(1) once more,
to get a result <= 1/2 of st(1). */
unsigned long long x;
expdif =
exponent16(&st1) - exponent16(&tmp);
if (expdif <= 1) {
if (expdif == 0)
x = significand(&st1) -
significand(&tmp);
else /* expdif is 1 */
x = (significand(&st1)
<< 1) -
significand(&tmp);
if ((x < significand(&tmp)) ||
/* or equi-distant (from 0 & st(1)) and q is odd */
((x == significand(&tmp))
&& (q & 1))) {
st0_sign = !st0_sign;
significand(&tmp) = x;
q++;
}
}
}
if (q & 4)
cc |= SW_C0;
if (q & 2)
cc |= SW_C3;
if (q & 1)
cc |= SW_C1;
} else {
control_word = old_cw;
setcc(0);
return;
}
} else {
/* There is a large exponent difference ( >= 64 ) */
/* To make much sense, the code in this section should
be done at high precision. */
int exp_1, N;
u_char sign;
/* prevent overflow here */
/* N is 'a number between 32 and 63' (p26-113) */
reg_copy(&st0, &tmp);
tmptag = st0_tag;
N = (expdif & 0x0000001f) + 32; /* This choice gives results
identical to an AMD 486 */
setexponent16(&tmp, N);
exp_1 = exponent16(&st1);
setexponent16(&st1, 0);
expdif -= N;
sign = getsign(&tmp) ^ st1_sign;
tag =
FPU_u_div(&tmp, &st1, &tmp,
PR_64_BITS | RC_CHOP | 0x3f, sign);
setsign(&tmp, sign);
FPU_round_to_int(&tmp, tag); /* Fortunately, this can't
overflow to 2^64 */
rem_kernel(significand(&st0),
&significand(&tmp),
significand(&st1),
significand(&tmp), exponent(&tmp)
);
setexponent16(&tmp, exp_1 + expdif);
/* It is possible for the operation to be complete here.
What does the IEEE standard say? The Intel 80486 manual
implies that the operation will never be completed at this
point, and the behaviour of a real 80486 confirms this.
*/
if (!(tmp.sigh | tmp.sigl)) {
/* The result is zero */
control_word = old_cw;
partial_status = saved_status;
FPU_copy_to_reg0(&CONST_Z, TAG_Zero);
setsign(&st0, st0_sign);
#ifdef PECULIAR_486
setcc(SW_C2);
#else
setcc(0);
#endif /* PECULIAR_486 */
return;
}
cc = SW_C2;
}
control_word = old_cw;
partial_status = saved_status;
tag = FPU_normalize_nuo(&tmp);
reg_copy(&tmp, st0_ptr);
/* The only condition to be looked for is underflow,
and it can occur here only if underflow is unmasked. */
if ((exponent16(&tmp) <= EXP_UNDER) && (tag != TAG_Zero)
&& !(control_word & CW_Underflow)) {
setcc(cc);
tag = arith_underflow(st0_ptr);
setsign(st0_ptr, st0_sign);
FPU_settag0(tag);
return;
} else if ((exponent16(&tmp) > EXP_UNDER) || (tag == TAG_Zero)) {
stdexp(st0_ptr);
setsign(st0_ptr, st0_sign);
} else {
tag =
FPU_round(st0_ptr, 0, 0, FULL_PRECISION, st0_sign);
}
FPU_settag0(tag);
setcc(cc);
return;
}
if (st0_tag == TAG_Special)
st0_tag = FPU_Special(st0_ptr);
if (st1_tag == TAG_Special)
st1_tag = FPU_Special(st1_ptr);
if (((st0_tag == TAG_Valid) && (st1_tag == TW_Denormal))
|| ((st0_tag == TW_Denormal) && (st1_tag == TAG_Valid))
|| ((st0_tag == TW_Denormal) && (st1_tag == TW_Denormal))) {
if (denormal_operand() < 0)
return;
goto fprem_valid;
} else if ((st0_tag == TAG_Empty) || (st1_tag == TAG_Empty)) {
FPU_stack_underflow();
return;
} else if (st0_tag == TAG_Zero) {
if (st1_tag == TAG_Valid) {
setcc(0);
return;
} else if (st1_tag == TW_Denormal) {
if (denormal_operand() < 0)
return;
setcc(0);
return;
} else if (st1_tag == TAG_Zero) {
arith_invalid(0);
return;
} /* fprem(?,0) always invalid */
else if (st1_tag == TW_Infinity) {
setcc(0);
return;
}
} else if ((st0_tag == TAG_Valid) || (st0_tag == TW_Denormal)) {
if (st1_tag == TAG_Zero) {
arith_invalid(0); /* fprem(Valid,Zero) is invalid */
return;
} else if (st1_tag != TW_NaN) {
if (((st0_tag == TW_Denormal)
|| (st1_tag == TW_Denormal))
&& (denormal_operand() < 0))
return;
if (st1_tag == TW_Infinity) {
/* fprem(Valid,Infinity) is o.k. */
setcc(0);
return;
}
}
} else if (st0_tag == TW_Infinity) {
if (st1_tag != TW_NaN) {
arith_invalid(0); /* fprem(Infinity,?) is invalid */
return;
}
}
/* One of the registers must contain a NaN if we got here. */
#ifdef PARANOID
if ((st0_tag != TW_NaN) && (st1_tag != TW_NaN))
EXCEPTION(EX_INTERNAL | 0x118);
#endif /* PARANOID */
real_2op_NaN(st1_ptr, st1_tag, 0, st1_ptr);
}