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fp-bit.c (_fpdiv_parts): Do not round when pack_d would round the same.

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* config/fp-bit.c (_fpdiv_parts): Do not round when pack_d would
	round the same.  When rounding, clear bits that would cause a
	second rounding in pack_d.
	(_fpmul_parts): Ditto.  Remove #if 0:d code.

From-SVN: r78951
This commit is contained in:
Hans-Peter Nilsson 2004-03-05 00:27:56 +00:00 • committed by Hans-Peter Nilsson
parent 5fd200f17f
commit fc7b80e449
2 changed files with 32 additions and 21 deletions
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7
gcc/ChangeLog
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@ -1,3 +1,10 @@
2004-03-05 Hans-Peter Nilsson <hp@axis.com>
* config/fp-bit.c (_fpdiv_parts): Do not round when pack_d would
round the same. When rounding, clear bits that would cause a
second rounding in pack_d.
(_fpmul_parts): Ditto. Remove #if 0:d code.
2004-03-04 Ziemowit Laski <zlaski@apple.com>
PR c++/14425, c++/14426

46
gcc/config/fp-bit.c
View file

@ -899,32 +899,28 @@ _fpmul_parts ( fp_number_type * a,
high |= 1;
low <<= 1;
}
/* rounding is tricky. if we only round if it won't make us round later. */
#if 0
if (low & FRACHIGH2)
{
if (((high & GARDMASK) != GARDMSB)
&& (((high + 1) & GARDMASK) == GARDMSB))
{
/* don't round, it gets done again later. */
}
else
{
high++;
}
}
#endif
if (!ROUND_TOWARDS_ZERO && (high & GARDMASK) == GARDMSB)
{
if (high & (1 << NGARDS))
{
/* half way, so round to even */
high += GARDROUND + 1;
/* Because we're half way, we would round to even by adding
GARDROUND + 1, except that's also done in the packing
function, and rounding twice will lose precision and cause
the result to be too far off. Example: 32-bit floats with
bit patterns 0xfff * 0x3f800400 ~= 0xfff (less than 0.5ulp
off), not 0x1000 (more than 0.5ulp off). */
}
else if (low)
{
/* but we really weren't half way */
/* We're a further than half way by a small amount corresponding
to the bits set in "low". Knowing that, we round here and
not in pack_d, because there we don't have "low" avaliable
anymore. */
high += GARDROUND + 1;
/* Avoid further rounding in pack_d. */
high &= ~(fractype) GARDMASK;
}
}
tmp->fraction.ll = high;
@ -1028,13 +1024,21 @@ _fpdiv_parts (fp_number_type * a,
{
if (quotient & (1 << NGARDS))
{
/* half way, so round to even */
quotient += GARDROUND + 1;
/* Because we're half way, we would round to even by adding
GARDROUND + 1, except that's also done in the packing
function, and rounding twice will lose precision and cause
the result to be too far off. */
}
else if (numerator)
{
/* but we really weren't half way, more bits exist */
/* We're a further than half way by the small amount
corresponding to the bits set in "numerator". Knowing
that, we round here and not in pack_d, because there we
don't have "numerator" avaliable anymore. */
quotient += GARDROUND + 1;
/* Avoid further rounding in pack_d. */
quotient &= ~(fractype) GARDMASK;
}
}