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Re^2: emulate 32-bit on perl 64

by Eliya (Vicar)
on Jan 11, 2012 at 16:55 UTC ( #947380=note: print w/replies, xml ) Need Help??

in reply to Re: emulate 32-bit on perl 64
in thread emulate 32-bit on perl 64

As long as you are very careful to use unsigned arithmetic and specify bitmasks that are no larger than the integer-size you know that you are using, code like this ought to be transportable.

Unfortunately, it's not always quite as simple in the general case.  For example, if the 32-bit code relies on specific overflow/wrap-over effects. Consider the following very simple case:

my $result = (0xffffffff + 2) & 0xffffffff; print $result;

Although the result is masked down to 32 bits, it differs depending on the perl being used:

32-bit perl: 4294967295 64-bit perl: 1

(I'm not saying it cannot be done, but it requires taking into account the specific overflow behavior, IV/UV to NV conversions of 32-bit perls, etc. — simple 0xffffffff AND-masking isn't enough.)

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Re^3: emulate 32-bit on perl 64
by Anonymous Monk on Apr 01, 2013 at 03:19 UTC
    Erm, *what*? Why does 32-bit perl (I just tested on MirBSD/i386, it does behave as you said) not wraparound? Urgh!

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