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Re: [perl #130133] [PATCH] Configure leaves garbage in$Config{longdblinfbytes}

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From:
Niko Tyni
Date:
November 19, 2016 07:40
Subject:
Re: [perl #130133] [PATCH] Configure leaves garbage in$Config{longdblinfbytes}
Message ID:
20161119074034.wfp6giewnq3bkwps@estella.local.invalid
On Fri, Nov 18, 2016 at 01:59:35PM -0800, James E Keenan via RT wrote:

> > Do you expect that the impact of this will only show up if someone is
> > using 'gcc' rather than, say, g++ or clang?

My guess is that the garbage doesn't have any functional impact.
The bytes seem to end up in PL_inf when long doubles are used, and I'd
expect any value with the right 80 bits will do for infinity there.

Perhaps Jarkko (cc'd) knows more? I think he's the long double expert
here :)

I noticed this because the Config.pm contents started to vary between
builds, breaking build reproducibility. We're not currently even using
long doubles in Debian, but these things apparently get probed for
regardless of that.

> FWIW, here's the diff I got when applying your patch to blead using this 'gcc':
> 
> #####
> gcc --version
> gcc (Ubuntu 5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609
> #####
> $ diff before.txt after.txt
> 1c1
> < longdblinfbytes='0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0xff, 0x7f, 0x40, 0x00, 0x00, 0x00, 0x00, 0x00';
> ---
> > longdblinfbytes='0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0xff, 0x7f, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00';
> #####
> 
> Is that what you would expect?

Yes; all of the last six bytes now get zeroed out like the code
seems to intend.
-- 
Niko Tyni   ntyni@debian.org

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