good chemistry is complicated, and a little bit messy -LW |
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PerlMonks |
Re: emulate 32-bit on perl 64by sundialsvc4 (Abbot) |
on Jan 11, 2012 at 15:58 UTC ( [id://947373]=note: print w/replies, xml ) | Need Help?? |
Probably the key improvement here is the use of hexadecimal notation: 0xffffffff instead of the corresponding, “magic” decimal. 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. (It might not be readable, heh, but it ought to be int-length agnostic.) I would almost edit my comment to say, don’t use “arithmetic” at all when you are bit-twiddling, as in code like this: That’s nasty... And I recognize at least one of those numbers, -2147483648, as an old, familiar 32-bit friend. I also detect the presence of signed arithmetic, dependent upon the thirty-first bit being the sign-bit. I suggest that this code should be rewritten to use bit-masking operators ... and to do so, perhaps, in a very specific way, as follows: If you want to mash-off, say, all but the rightmost 31 bits of an integer quantity, you should take: qty := qty and ( not 0x7fffffff );. (I am not using Perl notation here, for clarity.) The subexpression, (not 0x7fffffff), will evaluate to an int in which all bits are 1 except for the rightmost 31 bits, and it will do so correctly no matter what the sizeof(int) may be. So, I suggest that you need to go through code like this (fortunately, it is a small piece of code), work out what it is doing and then rewrite it. Construct a very thorough set of Test::More cases that you can run on both a 32-bit and a 64-bit system to prove that your rewrite is thoroughly correct.
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