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softfloat: Adjust parts_uncanon_normal for floatx80

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With floatx80_precision_x, the rounding happens across
the break between words.  Notice this case with

  frac_lsb = round_mask + 1 -> 0

and check the bits in frac_hi as needed.

In addition, since frac_shift == 0, we won't implicitly clear
round_mask via the right-shift, so explicitly clear those bits.
This fixes rounding for floatx80_precision_[sd].

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Richard Henderson 2020-11-21 16:35:54 -08:00
parent 8da5f1dbb0
commit 98b3cff753
1 changed files with 30 additions and 6 deletions
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36
fpu/softfloat-parts.c.inc
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@ -155,7 +155,13 @@ static void partsN(uncanon_normal)(FloatPartsN *p, float_status *s,
switch (s->float_rounding_mode) {
case float_round_nearest_even:
inc = ((p->frac_lo & roundeven_mask) != frac_lsbm1 ? frac_lsbm1 : 0);
if (N > 64 && frac_lsb == 0) {
inc = ((p->frac_hi & 1) || (p->frac_lo & round_mask) != frac_lsbm1
? frac_lsbm1 : 0);
} else {
inc = ((p->frac_lo & roundeven_mask) != frac_lsbm1
? frac_lsbm1 : 0);
}
break;
case float_round_ties_away:
inc = frac_lsbm1;
@ -176,7 +182,11 @@ static void partsN(uncanon_normal)(FloatPartsN *p, float_status *s,
overflow_norm = true;
/* fall through */
case float_round_to_odd_inf:
inc = p->frac_lo & frac_lsb ? 0 : round_mask;
if (N > 64 && frac_lsb == 0) {
inc = p->frac_hi & 1 ? 0 : round_mask;
} else {
inc = p->frac_lo & frac_lsb ? 0 : round_mask;
}
break;
default:
g_assert_not_reached();
@ -191,8 +201,8 @@ static void partsN(uncanon_normal)(FloatPartsN *p, float_status *s,
p->frac_hi |= DECOMPOSED_IMPLICIT_BIT;
exp++;
}
p->frac_lo &= ~round_mask;
}
frac_shr(p, frac_shift);
if (fmt->arm_althp) {
/* ARM Alt HP eschews Inf and NaN for a wider exponent. */
@ -201,18 +211,21 @@ static void partsN(uncanon_normal)(FloatPartsN *p, float_status *s,
flags = float_flag_invalid;
exp = exp_max;
frac_allones(p);
p->frac_lo &= ~round_mask;
}
} else if (unlikely(exp >= exp_max)) {
flags |= float_flag_overflow | float_flag_inexact;
if (overflow_norm) {
exp = exp_max - 1;
frac_allones(p);
p->frac_lo &= ~round_mask;
} else {
p->cls = float_class_inf;
exp = exp_max;
frac_clear(p);
}
}
frac_shr(p, frac_shift);
} else if (s->flush_to_zero) {
flags |= float_flag_output_denormal;
p->cls = float_class_zero;
@ -232,18 +245,29 @@ static void partsN(uncanon_normal)(FloatPartsN *p, float_status *s,
/* Need to recompute round-to-even/round-to-odd. */
switch (s->float_rounding_mode) {
case float_round_nearest_even:
inc = ((p->frac_lo & roundeven_mask) != frac_lsbm1
? frac_lsbm1 : 0);
if (N > 64 && frac_lsb == 0) {
inc = ((p->frac_hi & 1) ||
(p->frac_lo & round_mask) != frac_lsbm1
? frac_lsbm1 : 0);
} else {
inc = ((p->frac_lo & roundeven_mask) != frac_lsbm1
? frac_lsbm1 : 0);
}
break;
case float_round_to_odd:
case float_round_to_odd_inf:
inc = p->frac_lo & frac_lsb ? 0 : round_mask;
if (N > 64 && frac_lsb == 0) {
inc = p->frac_hi & 1 ? 0 : round_mask;
} else {
inc = p->frac_lo & frac_lsb ? 0 : round_mask;
}
break;
default:
break;
}
flags |= float_flag_inexact;
frac_addi(p, p, inc);
p->frac_lo &= ~round_mask;
}
exp = (p->frac_hi & DECOMPOSED_IMPLICIT_BIT) != 0;