Re: [ID 20010723.001] perl 5.6.1: BigInt booleans cannot handle negatives

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Moin Bryce,

>And, Or, and Xor on two positive BigInts seem to work ok.  However, if you
>throw in a negative operand you get some very strange behavior.  I'm
>assuming that you would like integer math and bigint math to be compatible
>here, but even without that assumption BigInt is still buggy.  Here is a
>testing script which runs on perl 5.6.1.  (It uses booleans on a BigInt so
>only recent perls will run it at all.)
>
>use Math::BigInt;
>@list = (-65536, -65535, -1, 0, 1, 65535, 65536);
>foreach $x (@list) {
>  foreach $y (@list) {
>    $a = $x & $y;
>    $b = (Math::BigInt->new($x)) & (Math::BigInt->new($y));
>    if ($a != $b) { 
>      print "MISMATCH:\n";
>      print "$x AND $y = $a   (integer math)\n";
>      print "$x AND $y = $b   (BigInt math)\n";
>    }
>  }
>}
>
>The problem seems to be that the BigInt boolean functions do not sign
>extend negative numbers when they are breaking them into chunks with bdiv.
> 
>This job would be easy if the numbers were stored in a base that is a
>power of 2 instead of a power of 10.  (Then you could do left and right
>shift without dividing as well...)
>
>Thank you,
>Bryce Denney

Thank you for your bug-report. While the problem with negatives should be
probably addressed in the latest version (v1.38, and v1.39 imminent), my
local v1.39 shows another bug: it loops forever.

I will fix this ASAP.

Best regards,

Tels


- -- 
perl -MMath::String -e 'print \
Math::String->from_number("215960156869840440586892398248"),"\n"'

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• [ID 20010723.001] perl 5.6.1: BigInt booleans cannot handle negatives by Bryce Denney
• Re: [ID 20010723.001] perl 5.6.1: BigInt booleans cannot handle negatives by Tels