defining large datatypes

Discussion in 'C Programming' started by Nimo, Dec 29, 2010.

  1. Nimo

    Nimo Guest


    how to deal with numbers which has more than 20 digits..

    as I can use a maximum of 'long long'; is there any way to handle
    these type of values?

    what data type I've to define? and is there any library available to
    do these type of calclulations?

    Thank You.
    so long..
    Nimo, Dec 29, 2010
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  2. Google bignum or "arbitrary precision arithmetic", should get you
    going. Could start here:
    Yes, need a library. If you don't need precise answers, could use
    doubles depending on your application and the range of values needed.

    David Resnick, Dec 29, 2010
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  3. Nimo

    Angus Guest

    Or you could use a char array. But you would have to handle addition,
    subtraction etc. But then you could support an unlimited number
    size. The big int libraries will do all this for you in a very
    efficient way.
    Angus, Dec 31, 2010
  4. Nimo

    BGB Guest

    I have some library code to do arithmetic directly using ASCII strings
    for input/output.

    technically, it supports fairly large numbers (I forget the current max
    size, and IIRC was something like 2048.2048 decimal digits or similar,
    but it is adjustable anyways...).

    more often, smaller fixed-size numbers are more useful though, say,
    using a fixed 128 bit number or such...

    but, yeah, between using a bignum library or writing it themselves,
    either is an option.

    supporting variable-sized numbers is more generic, but is a little
    harder to do as efficiently, since the logic has to be generic for
    whatever input size it is passed (and even then, there needs to be some
    practical limit to how big a number can be).

    some claim "the number can be as big as there is memory to store it",
    but often even such an implementation would be impractical (one needs
    temporary memory to store intermediate results, or memory may be
    fragmented, or say only 16 bits are used to store the number of machine
    words in the result, or...).

    and really, what is the liklihood of a person needing
    multi-billion-digit numbers anyways?...

    "the number may be absurdly huge" or "the number may be up to 629k
    digits" or similar is plenty reasonable, without invoking the "numbers
    as big as memory" claim.

    or such...
    BGB, Jan 3, 2011
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