half an int

This is a discussion on half an int within the C++ Programming forums, part of the General Programming Boards category; Hello all, just a quick quest: is half an unsigned int 0x80000000 or 0x7FFFFFFF? 0xFFFFFFFF / 2 = 0x7FFFFFFF but ...

  1. #1
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    half an int

    Hello all, just a quick quest:

    is half an unsigned int 0x80000000 or 0x7FFFFFFF?

    0xFFFFFFFF / 2 = 0x7FFFFFFF

    but

    0x7FFFFFFF * 2 = 0xFFFFFFFE

    (note the trailing E)

    and

    0x80000000 * 2 = 0x0 (or more exactly 0x100000000 (9 digits))

    I opt for 0x7FFFFFFF (as 2 * the half shouldnt be 0!)

    Any comments or thoughts?

  2. #2
    Programming Sex-God Polymorphic OOP's Avatar
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    0x7FFFFFFF

    would be "half" of an unsigned 32 bit integer, though "half" is a rather silly term for it. A 32 integer holds an even number of values, but you have to remember that the values start at 0 not 1, so dividing directly by 2 will give you a fraction. What you'd do is divide 2^32 by 2 and then subtract 1 from it to get "half" full. Since the "value" of 0xFFFFFFFF is odd, you can't multiply an integer by 2 to get it.

    The reason you are getting 0 for 0x80000000 * 2 is because that goes 1 over the maximum amount that a 32 bit integer can hold. The numbers "rolled over" back to 0.
    Last edited by Polymorphic OOP; 12-16-2002 at 01:28 AM.

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