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Re: [bug-gawk] MPFR rounding issue
From: |
Andrew J. Schorr |
Subject: |
Re: [bug-gawk] MPFR rounding issue |
Date: |
Mon, 20 Nov 2017 13:00:05 -0500 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Mon, Nov 20, 2017 at 10:52:25AM -0700, david kerns wrote:
> I'm sorry I can't assist with actual test data, but compare the results of
> 2.21 vs (3.21 or 2.31)
bash-4.2$ printf "2.21\n3.21\n2.31\n" | gawk -M -v ROUNDMODE=A '{printf
"%.1f\n", $1}'
2.3
3.3
2.4
It rounds up in all cases. Isn't that the intended behavior of
the MPFR_RNDA? The mpfr docs define it as:
* `MPFR_RNDA': round away from zero.
> reference https://en.wikipedia.org/wiki/Rounding?#Round_half_to_even ...
But this is not "half-to-even" rounding mode. It is "round away from zero".
> BTW I might be completely off kilter on this :P
> but as Andy notes, it's just using the value the MPFR library returned
I'm not an expert in this stuff, but the behavior seems consistent with
the MPFR docs.
Maybe the problem is in the gawk docs. In the "Setting the Rounding Mode"
section of the manual, it says:
https://www.gnu.org/software/gawk/manual/html_node/Setting-the-rounding-mode.html
Rounding mode IEEE name ROUNDMODE
Round to nearest, ties to even roundTiesToEven "N" or "n"
Round toward positive infinity roundTowardPositive "U" or "u"
Round toward negative infinity roundTowardNegative "D" or "d"
Round toward zero roundTowardZero "Z" or "z"
Round to nearest, ties away from zero roundTiesToAway "A" or "a"
So maybe that's the confusion. The gawk documentation of "A" says
"Round to nearest, ties away from zero", but the actual implementation uses
MPFR_RNDA, which rounds away from zero.
Perhaps this is simply a bug in the gawk documentation?
Regards,
Andy
- [bug-gawk] (no subject), David Kaspar [Dee'Kej], 2017/11/20
- Re: [bug-gawk] (no subject), David Kaspar [Dee'Kej], 2017/11/20
- Re: [bug-gawk] MPFR rounding issue, Andrew J. Schorr, 2017/11/20
- Re: [bug-gawk] MPFR rounding issue, david kerns, 2017/11/20
- Re: [bug-gawk] MPFR rounding issue,
Andrew J. Schorr <=
- Re: [bug-gawk] MPFR rounding issue, arnold, 2017/11/20
- Re: [bug-gawk] MPFR rounding issue, Andrew J. Schorr, 2017/11/20
- Re: [bug-gawk] MPFR rounding issue, David Kaspar [Dee'Kej], 2017/11/21
- Re: [bug-gawk] MPFR rounding issue, Andrew J. Schorr, 2017/11/21
- Re: [bug-gawk] MPFR rounding issue, arnold, 2017/11/21
- Re: [bug-gawk] MPFR rounding issue, Andrew J. Schorr, 2017/11/21
- Re: [bug-gawk] MPFR rounding issue, arnold, 2017/11/21