contrib/gmp/mpz/gcd_ui.c

   1 /* mpz_gcd_ui -- Calculate the greatest common divisor of two integers.
   2
   3 Copyright 1994, 1996, 1999, 2000, 2001, 2002, 2003, 2004 Free Software
   4 Foundation, Inc.
   5
   6 This file is part of the GNU MP Library.
   7
   8 The GNU MP Library is free software; you can redistribute it and/or modify
   9 it under the terms of the GNU Lesser General Public License as published by
  10 the Free Software Foundation; either version 3 of the License, or (at your
  11 option) any later version.
  12
  13 The GNU MP Library is distributed in the hope that it will be useful, but
  14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  15 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  16 License for more details.
  17
  18 You should have received a copy of the GNU Lesser General Public License
  19 along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
  20
  21 #include <stdio.h> /* for NULL */
  22 #include "gmp.h"
  23 #include "gmp-impl.h"
  24
  25 unsigned long int
  26 mpz_gcd_ui (mpz_ptr w, mpz_srcptr u, unsigned long int v)
  27 {
  28   mp_size_t un;
  29   mp_limb_t res;
  30
  31 #if BITS_PER_ULONG > GMP_NUMB_BITS  /* avoid warnings about shift amount */
  32   if (v > GMP_NUMB_MAX)
  33     {
  34       mpz_t vz;
  35       mp_limb_t vlimbs[2];
  36       vlimbs[0] = v & GMP_NUMB_MASK;
  37       vlimbs[1] = v >> GMP_NUMB_BITS;
  38       PTR(vz) = vlimbs;
  39       SIZ(vz) = 2;
  40       mpz_gcd (w, u, vz);
  41       /* because v!=0 we will have w<=v hence fitting a ulong */
  42       ASSERT (mpz_fits_ulong_p (w));
  43       return mpz_get_ui (w);
  44     }
  45 #endif
  46
  47   un = ABSIZ(u);
  48
  49   if (un == 0)
  50     res = v;
  51   else if (v == 0)
  52     {
  53       if (w != NULL)
  54         {
  55           if (u != w)
  56             {
  57               MPZ_REALLOC (w, un);
  58               MPN_COPY (PTR(w), PTR(u), un);
  59             }
  60           SIZ(w) = un;
  61         }
  62       /* Return u if it fits a ulong, otherwise 0. */
  63       res = PTR(u)[0];
  64       return (un == 1 && res <= ULONG_MAX ? res : 0);
  65     }
  66   else
  67     res = mpn_gcd_1 (PTR(u), un, (mp_limb_t) v);
  68
  69   if (w != NULL)
  70     {
  71       PTR(w)[0] = res;
  72       SIZ(w) = res != 0;
  73     }
  74   return res;
  75 }