Re: [Dev-C++] Overflow detection (was No Subject)

[David M. <ci...@ya...>]

Ok, point taken. I am not going to stop though. For me this
is another of my
personal projects that help me learn. Guess I will point
them towards GMP
and the Large Number class on sourceforge.net (a class I am
fighting to
understand as I see alot of pre-processor directives).

No assembly! I am fighting for portability, asm is one of
the fastest ways
to break that portability. Damn, I am such an idiot. That
would work
extremly well! Thanks! The only difference is I add the
overflow to the next
block. The only bit I was worrying about was the carry bit.

Thanks Per

Signed
David McKen

----- Original Message ----- 
From: "Per Westermark" <pw...@ia...>
To: "David McKen" <ci...@ya...>
Cc: "Dev-C Mailing List"
<dev...@li...>
Sent: Thursday, October 09, 2003 9:57 AM
Subject: Re: [Dev-C++] Overflow detection (was No Subject)


> 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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