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

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From:
Jarkko Hietaniemi via RT
Date:
November 19, 2016 12:56
Subject:
[perl #130133] [PATCH] Configure leaves garbage in$Config{longdblinfbytes}
Message ID:
rt-4.0.24-22345-1479560181-1683.130133-15-0@perl.org
> Perhaps Jarkko (cc'd) knows more? I think he's the long double expert
> here :)

Yeah, beyond the 80 bits there might be any random garbage, and the
random bits might appear there at any point.  I am guessing at the
discretion of whatever the compiler thinks work best (most probably 
fast-est) at any given time those bytes are looked at / manipulated.
And the garbage doesn't affect the long double computations.

(FWIW, I think there have been in the past x86-platform compilers
where the long doubles have been 12 bytes, on 32-bit platforms,
so those had only two garbage bytes.)

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

Didn't stop me getting the long doubles probing code wrong, though.

> 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.



---
via perlbug:  queue: perl5 status: open
https://rt.perl.org/Ticket/Display.html?id=130133

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