Re: long long with libpari

[Karim BELABAS <Karim.Belabas@math.u-psud.fr>]

[Janet:]
> I'm wondering if there is a way to use really big integers with libpari
> (where a really big integer is one that requires more space than a long).
> It seems like stoi is the only function to stuff an integer into a GEN
> (perhaps I'm wrong on this point?), and this automatically converts the
> integer to a long first.  Is there anything I can do to get bigger
> integers?

You can convert from a string:

  GEN x = lisexpr("123456768912312312391273198372131");

But most "interesting" integers are the result of some computation, so you
can program that computation, e.g 

  GEN x = addis( gpowgs(stoi(3), 1000), 7 );  /* 3^1000 + 7 */

If what you want is a low-level function to convert from "long long" to PARI
integer, you'll have to copy the code from stoi and modify it to your
liking. Something like

  GEN
  lltoi(long long x)
  {
    GEN y;

    if ((x >> BITS_IN_LONG) == 0) return stoi((long)x);
    y = cgeti(4);
    if (x > 0)
    {
       y[1] = evalsigne(1)  | evallgefint(4);
    }
    else
    {
       y[1] = evalsigne(-1) | evallgefint(4);
       x = -x;
    }
    y[2] = x >> BITS_IN_LONG;
    y[3] = (long)x;
    return y;
  }

[untested, but should work after minimal tweaking...]

Cheers,

    Karim.
-- 
Karim Belabas                    email: Karim.Belabas@math.u-psud.fr
Dep. de Mathematiques, Bat. 425
Universite Paris-Sud             Tel: (00 33) 1 69 15 57 48
F-91405 Orsay (France)           Fax: (00 33) 1 69 15 60 19
--
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