From: Endlisnis AT yahoo DOT com (Rolf Campbell)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: 128 bit integer
Date: 8 Aug 2001 10:09:53 -0700
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Kai Dietrich <toepferei DOT dietrich AT t-online DOT de> wrote in message news:<9krgph$496$04$1 AT news DOT t-online DOT com>...
> Hmm, obviosly I havn't said enough. GMP is not exactly what I
>  want. I need a constant size like
> class  int128
> {
> public:
> long long v[2];
> };
[snip]
> I want the solution to behave like long long but with 128 bits
>  (256 or more would be OK, too) instead of 64. I know that it is
>  possible, it is the same solution like getting long long working
>  on a 32bit machine. I would be able to combined two long long
>  but I can only write + not - :-(. I need a little bit help
>  writing
>  int128 add( int128 a,  int128 b);
>  int128 sub( int128 a,  int128 b);

Well, if you are going to use classes, you might as well use operators, so:
int128 operator - (const int128& a, const int128& b)
{
  return a + -b;
  }

Then implement unary minus something like (warning: untested code):

int128 operator - (const int128& b)
{
  int128 ret(b);
  ret.v[0] = ~ret.v[0];
  ret.v[1] = ~ret.v[1];
  return ret+1;
  }