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Custom Data Type for Huge Numbers

Discussion in 'C++' started by rivaskh, Aug 9, 2008.

  1. rivaskh

    rivaskh New Member

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    Hi,

    Is there any way that I can do a following initialization?

    DataType abc = 22222222222222222222222;

    where the value is a huge number larger than 2^32.
     
  2. erislover

    erislover New Member

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    Probably not. But check out gmplib.org for a library that could help you.
     
  3. erislover

    erislover New Member

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    Well, by "probably not" I'm assuming you need something larger than 64 bits, available on every 32-bit system I'm aware of. If you're working in embedded systems where 32 bits is already your largest built-in data type, then you must code up your own functions and declarations to deal with larger numbers. This is much easier in C++ than C because of operator overloading. If you are working with C++ then google will help you find plenty of good resources for hand-rolling what you need, if you don't want to use GMP.
     
  4. xpi0t0s

    xpi0t0s Mentor

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    No, because 22222222222222222222222 is an invalid number and will be picked up by the compiler as an error.
    However you could encode the number differently, for example using strings:
    DataType abc = "22222222222222222222222";
     
  5. rivaskh

    rivaskh New Member

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    True... I was wondering if I could create a a class that coupled a lot of integers together to form a super integer that could take values higher than 32 bit with it having the same operations as a primitive integer type. This way, I could use it in place of unsigned int and still retain my code without too much change.
     
  6. xpi0t0s

    xpi0t0s Mentor

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    Yes of course, that's the whole point of operator overloading in C++. In C++ you can fairly easily write something like
    Code:
    MyBigNumCls num1(23,75,62); // a constructor that takes 3 integers
    MyBigNumCls num2(49,11,51);
    MyBigNumCls result=num1+num2;
    
    So num1(23,75,62) could represent 23<<64 | 75<<32 | 62 and it's up to you how to store it, as three integers if you like. With the above code result, assuming you've defined MyBigNumCls::eek:perator +(), would then represent (23+49)<<64 | (75+11)<<32 | (62+51)

    This is easy to do; have a go and see how far you get. For multiplication and division just look back to how you used to do it at school on paper then implement that algorithm.
     

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