Are you also sick of the existing large-number libraries that exists, and
that supports any number of digits up to size of available memory?
To my knowledge, you can't write a portable implementation using
overflow exceptions. The normal method is for example to perform all
big-number arithmetic with unsigned numbers and a separately stored sign
bit.
Then you get:
r0 = a0 + b0;
overflow = r0 < a0 || r0 < b0;
r1 = a1 + b1 + overflow;
...
No need to work on bit level.
If implemented in assembly, the
overflow = r0 < a0 || r0 < b0
can be ignored, since an overflow would result in the carry bit being set
in the processor flag register - all processors have support for carry
bit.
/Per W
On Thu, 9 Oct 2003, David McKen wrote:
> No I don't require it to be standard, however I would like
> it to be standard.
>
> My current focus are speed and portability. The reason why
> 64 bit won't sufice is because I would like to take a try
> at the RSA factoring challenge:
>
> http://www.rsasecurity.com/rsalabs/challenges/factoring/faq.html
>
> And if you look throught you will eventually find the
> challenge numbers at
>
> http://www.rsasecurity.com/rsalabs/challenges/factoring/numbers.html
>
> IF you take a look at those numbers then you will quickly
> see why 64 bit is too small. Besides if I complete this
> class I know at least 3-4 people who would use it because
> they are sick of the 4 billlion limitation put on them.
>
> Thanks for your Help
>
> Signed
> David McKen
>
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