public inbox for gcc-cvs@sourceware.org
help / color / mirror / Atom feed
* [gcc r13-4551] range-op-float: frange_arithmetic tweaks for MODE_COMPOSITE_P
@ 2022-12-08 9:43 Jakub Jelinek
0 siblings, 0 replies; only message in thread
From: Jakub Jelinek @ 2022-12-08 9:43 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:716c2d08893110f186f0fb94849524b1acf9dd02
commit r13-4551-g716c2d08893110f186f0fb94849524b1acf9dd02
Author: Jakub Jelinek <jakub@redhat.com>
Date: Thu Dec 8 10:41:49 2022 +0100
range-op-float: frange_arithmetic tweaks for MODE_COMPOSITE_P
As mentioned in PR107967, ibm-ldouble-format documents that
+- has 1ulp accuracy, * 2ulps and / 3ulps.
So, even if the result is exact, we need to widen the range a little bit.
The following patch does that. I just wonder what it means for reverse
division (the op1_range case), which we implement through multiplication,
when division has 3ulps error and multiplication just 2ulps. In any case,
this format is a mess and for non-default rounding modes can't be trusted
at all, instead of +inf or something close to it it happily computes -inf.
2022-12-08 Jakub Jelinek <jakub@redhat.com>
* range-op-float.cc (frange_nextafter): For MODE_COMPOSITE_P from
denormal or zero, use real_nextafter on DFmode with conversions
around it.
(frange_arithmetic): For mode_composite, on top of rounding in the
right direction accept extra 1ulp error for PLUS/MINUS_EXPR, extra
2ulps error for MULT_EXPR and extra 3ulps error for RDIV_EXPR.
Diff:
---
gcc/range-op-float.cc | 62 ++++++++++++++++++++++++++++++++++++++-------------
1 file changed, 46 insertions(+), 16 deletions(-)
diff --git a/gcc/range-op-float.cc b/gcc/range-op-float.cc
index 2c6026d48fa..929ff9c3f87 100644
--- a/gcc/range-op-float.cc
+++ b/gcc/range-op-float.cc
@@ -254,10 +254,21 @@ frange_nextafter (enum machine_mode mode,
REAL_VALUE_TYPE &value,
const REAL_VALUE_TYPE &inf)
{
- const real_format *fmt = REAL_MODE_FORMAT (mode);
- REAL_VALUE_TYPE tmp;
- real_nextafter (&tmp, fmt, &value, &inf);
- value = tmp;
+ if (MODE_COMPOSITE_P (mode)
+ && (real_isdenormal (&value, mode) || real_iszero (&value)))
+ {
+ // IBM extended denormals only have DFmode precision.
+ REAL_VALUE_TYPE tmp, tmp2;
+ real_convert (&tmp2, DFmode, &value);
+ real_nextafter (&tmp, REAL_MODE_FORMAT (DFmode), &tmp2, &inf);
+ real_convert (&value, mode, &tmp);
+ }
+ else
+ {
+ REAL_VALUE_TYPE tmp;
+ real_nextafter (&tmp, REAL_MODE_FORMAT (mode), &value, &inf);
+ value = tmp;
+ }
}
// Like real_arithmetic, but round the result to INF if the operation
@@ -324,21 +335,40 @@ frange_arithmetic (enum tree_code code, tree type,
}
if (round && (inexact || !real_identical (&result, &value)))
{
- if (mode_composite)
+ if (mode_composite
+ && (real_isdenormal (&result, mode) || real_iszero (&result)))
{
- if (real_isdenormal (&result, mode)
- || real_iszero (&result))
- {
- // IBM extended denormals only have DFmode precision.
- REAL_VALUE_TYPE tmp;
- real_convert (&tmp, DFmode, &value);
- frange_nextafter (DFmode, tmp, inf);
- real_convert (&result, mode, &tmp);
- return;
- }
+ // IBM extended denormals only have DFmode precision.
+ REAL_VALUE_TYPE tmp, tmp2;
+ real_convert (&tmp2, DFmode, &value);
+ real_nextafter (&tmp, REAL_MODE_FORMAT (DFmode), &tmp2, &inf);
+ real_convert (&result, mode, &tmp);
}
- frange_nextafter (mode, result, inf);
+ else
+ frange_nextafter (mode, result, inf);
}
+ if (mode_composite)
+ switch (code)
+ {
+ case PLUS_EXPR:
+ case MINUS_EXPR:
+ // ibm-ldouble-format documents 1ulp for + and -.
+ frange_nextafter (mode, result, inf);
+ break;
+ case MULT_EXPR:
+ // ibm-ldouble-format documents 2ulps for *.
+ frange_nextafter (mode, result, inf);
+ frange_nextafter (mode, result, inf);
+ break;
+ case RDIV_EXPR:
+ // ibm-ldouble-format documents 3ulps for /.
+ frange_nextafter (mode, result, inf);
+ frange_nextafter (mode, result, inf);
+ frange_nextafter (mode, result, inf);
+ break;
+ default:
+ break;
+ }
}
// Crop R to [-INF, MAX] where MAX is the maximum representable number
^ permalink raw reply [flat|nested] only message in thread
only message in thread, other threads:[~2022-12-08 9:43 UTC | newest]
Thread overview: (only message) (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-12-08 9:43 [gcc r13-4551] range-op-float: frange_arithmetic tweaks for MODE_COMPOSITE_P Jakub Jelinek
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).