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Converting signed hex back to a decimal???

Posted on 2002-03-06
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Last Modified: 2008-03-06
Hi all, just wondering how to convert a hex number which is negative to it's decimal equivalent.

So if I had the number '0xFE' it would output it's decimal number (which would have originally been negative).

Any ideas?
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Question by:OnlyOne
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japhyRPI earned 50 total points
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You want to use the hex() function; however, hex("0xFE") would return 254, not -2 (as I assume you would like).  On the other hand, hex("0xFFFFFFFE") still returns 4294967294, not -2.

If you need to enforce signed-ness, that's a different story.  Assuming you have an eight-character hex number (like "FFFFFFFE"), you can use the following code:

  $number =
    unpack "i",      # decode as a signed integer
    pack "I",        # encode as an unsigned integer
    hex("0x$hnum");  # convert 0x........ to integer

When I set $hnum to "FFFFFFFE", I get -2 in $number.
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by:japhyRPI
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I just realized that if you have a two-character hex value, such as "FE", you can use the "c" and "C" pack/unpack template.

  $number =       # so it gets -2
    unpack "c",   # unpacked as signed char
    pack "C",     # packed as unsigned char
    hex("0xFE");  # returns 254
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by:maneshr
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OnlyOne,

"..convert a hex number which is negative to it's decimal equivalent...."

Here is a small script that might work for you.

#!/usr/local/bin/perl

$hexadecimal='0xFE';
$number = hex($hexadecimal);         # hexadecimal

print $number,"\n";

Hope that helps.

"..(which would have originally been
                     negative)..."

i am not sure if the above code solves this part.
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by:OnlyOne
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Well done, japhyRPI, that was right on the money.

Keep up the good work!
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