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

Dear Monks,

I'm anticipating a "don't do that" response to this question, but I'm hoping for some clever trickery to help me solve this problem anyway.

I have a device driver that prints an int as an unsigned 32-bit value, so it displays "-1" as "4294967295."

My 64-bit perl v5.8.9 binary displays the same value as a twos-complement 64-bit value, so "-1" as "18446744073709551615."

I need to compare the values, ideally in string format.

I can't change the device driver, and I'm hoping to be able to use 64-bit perl. Does anyone know of a printf modifier (or some other approach) that specifies the length of the argument as 4 bytes? I know %hu works with perl, I'm hoping for something similar for 4-byte values.

Thanks!

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Re: printf formatting 32 bit values
by BrowserUk (Patriarch) on Sep 28, 2010 at 21:39 UTC

    If you and the value with 0xffffffff, it will trim it to 32-bits: 

    print unpack 'Q', pack 'Q', -1;;
18446744073709551615

print unpack 'Q', pack 'Q', -1 & 0xffffffff;;
4294967295

    [download]

    Is that the sort of thing you are looking for?

    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
[d/l]
      Yep, that does it. The pack'ing was the part I was missing ... sign extending 0x000000000ffffffff didn't work.

      thank you
[reply]

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