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From: "newbie-02 at gmx dot de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/113455] New: ROUNDING: IEEE Standard: Missing decimal
 rounding mode 'nearest, ties away from zero' for decimalxxx datatypes.
Date: Wed, 17 Jan 2024 17:41:10 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113455

            Bug ID: 113455
           Summary: ROUNDING: IEEE Standard: Missing decimal rounding mode
                    'nearest, ties away from zero' for decimalxxx
                    datatypes.
           Product: gcc
           Version: 13.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: newbie-02 at gmx dot de
  Target Milestone: ---

hi @all,=20=20

most likely 'me bad', but searched too long and need professional help.=20=
=20

Short - just need a tip:=20=20=20
A.) me blind, 'ties away' is available,=20=20
in that case how to activate? or=20=20
B.) no hope, 'ties away' is NOT available,=20=20
in that case evtl. 'why?', and if planned for the future?=20=20
Or doe's someone know a workaround?=20=20

what I'd like to have:=20=20
'=3D 8.000000000000001DD + 0.5E-15DD' -> 8.000000000000002E+00=20=20
'=3D 8.000000000000002DD + 0.5E-15DD' -> 8.000000000000003E+00=20=20
not by 'round up', but by 'round nearest, ties away from zero'.=20=20

what I get instead:=20=20
'=3D 8.000000000000001DD + 0.5E-15DD' -> 8.000000000000002E+00=20=20
'=3D 8.000000000000002DD + 0.5E-15DD' -> 8.00000000000000**2**E+00=20=20
the second calculation suffers from 'ties to even' rounding mode.=20=20

'The standard' IEEE 754 requires a decimal rounding mode=20=20
'nearest, ties away from zero' since 2008, see=20=20
http://www.dsc.ufcg.edu.br/~cnum/modulos/Modulo2/IEEE754_2008.pdf=20=20
there '4.3.3 Rounding attribute requirements'.=20=20

I **am** aware that gcc / glibc don't claim full standard=20=20
compatibility for 'decimals', but consider the rounding mode=20=20
one of the most important advantages.=20=20

I **am** aware that 'ties away' is in effect for 'round'=20=20
operations. But couldn't find how to activate for the implicit=20=20
rounding in calculations.=20=20

I **am** aware that there are near religious fanatic discussions=20=20
about which rounding is 'better', I don't want to start similar,=20=20
just get qualified info. Posted here despite I know it's not a=20=20
user support forum, think the info is relevant for others too.=20=20

In case of relevant: Intel, Linux, gcc.=