kiramind has asked for the wisdom of the Perl Monks concerning the following question:

Hello, It appears that past a certain value, `localtime` stops returning dates. thanks to a binary search performed by one of my colleagues, it appear the magic number is `67767976233316804` (which is between 2**55 and 2**56). 
> perl -E 'say "#1> ".localtime(67767976233316804); say "#2> ".localti
+me(67767976233316805); '
#1> Sun Dec 29 21:00:00 2147483647
#2>

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I am a little curious as why is this value the biggest one accepted. Do some monks have this knowledge ?

Replies are listed 'Best First'.
Re: Maximum localtime value in Perl
by NetWallah (Canon) on May 08, 2018 at 03:49 UTC
    The maximum ((update) signed) 32-bit int is 2,147,483,647 == (2^31)-1 .

    If you notice - this is the value of the "year" produced in #1.

    This value corresponds to 0x7FFFFFFF.

    IMHO, localtime should create an "integer Overflow" type exception beyond this value, or start using 64-bit ints.

                    Memory fault   --   brain fried

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Re: Maximum localtime value in Perl
by mxb (Pilgrim) on May 08, 2018 at 08:31 UTC

    I can replicate here also.

    % perl --version
This is perl 5, version 24, subversion 4 (v5.24.4) built for 
amd64-freebsd-thread-multi

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    From perldoc perlport

    gmtime  In theory, "gmtime()" is reliable from -2**63 to 2**63-1.
        However, because work arounds in the implementation use
        floating point numbers, it will become inaccurate as the time
        gets larger. This is a bug and will be fixed in the future.

        On VOS, time values are 32-bit quantities.

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Re: Maximum localtime value in Perl
by thomas895 (Deacon) on May 08, 2018 at 02:22 UTC

    I can replicate this on v5.12.3 on Win32. What version are you using?

    I think it's not just Perl but the localtime function itself that causes this.

    -Thomas
    "Excuse me for butting in, but I'm interrupt-driven..."
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      I am using perl v5.18.2 on Mac OSX.
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Re: Maximum localtime value in Perl
by choroba (Cardinal) on May 09, 2018 at 06:47 UTC
    Based on Nostradamus' famous prediction, the world as we know it will end on that day. There's no point in returning localtime for any future moment.

    ($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,

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      At that point in the future the planck length will shrink to zero, causing the whole universe to implode into a singular non-point of nothingness in no time.

      perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'
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        Don't be a tease!

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      Now that made me wonder if localtime() should handle complex numbers. And how.

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