source/libs/gmp/gmp-src/mpz/gcdext.c

   1 /* mpz_gcdext(g, s, t, a, b) -- Set G to gcd(a, b), and S and T such that
   2    g = as + bt.
   3
   4 Copyright 1991, 1993-1997, 2000, 2001, 2005, 2011, 2012 Free Software
   5 Foundation, Inc.
   6
   7 This file is part of the GNU MP Library.
   8
   9 The GNU MP Library is free software; you can redistribute it and/or modify
  10 it under the terms of either:
  11
  12   * the GNU Lesser General Public License as published by the Free
  13     Software Foundation; either version 3 of the License, or (at your
  14     option) any later version.
  15
  16 or
  17
  18   * the GNU General Public License as published by the Free Software
  19     Foundation; either version 2 of the License, or (at your option) any
  20     later version.
  21
  22 or both in parallel, as here.
  23
  24 The GNU MP Library is distributed in the hope that it will be useful, but
  25 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  26 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  27 for more details.
  28
  29 You should have received copies of the GNU General Public License and the
  30 GNU Lesser General Public License along with the GNU MP Library.  If not,
  31 see https://www.gnu.org/licenses/.  */
  32
  33 #include <stdio.h> /* for NULL */
  34 #include "gmp.h"
  35 #include "gmp-impl.h"
  36
  37 void
  38 mpz_gcdext (mpz_ptr g, mpz_ptr s, mpz_ptr t, mpz_srcptr a, mpz_srcptr b)
  39 {
  40   mp_size_t asize, bsize;
  41   mp_ptr tmp_ap, tmp_bp;
  42   mp_size_t gsize, ssize, tmp_ssize;
  43   mp_ptr gp, tmp_gp, tmp_sp;
  44   TMP_DECL;
  45
  46   /* mpn_gcdext requires that Usize >= Vsize.  Therefore, we often
  47      have to swap U and V.  The computed cofactor will be the
  48      "smallest" one, which is faster to produce.  The wanted one will
  49      be computed here; this is needed anyway when both are requested.  */
  50
  51   asize = ABSIZ (a);
  52   bsize = ABSIZ (b);
  53
  54   if (asize < bsize)
  55     {
  56       MPZ_SRCPTR_SWAP (a, b);
  57       MP_SIZE_T_SWAP (asize, bsize);
  58       MPZ_PTR_SWAP (s, t);
  59     }
  60
  61   if (bsize == 0)
  62     {
  63       /* g = |a|, s = sgn(a), t = 0. */
  64       ssize = SIZ (a) >= 0 ? (asize != 0) : -1;
  65
  66       gp = MPZ_REALLOC (g, asize);
  67       MPN_COPY (gp, PTR (a), asize);
  68       SIZ (g) = asize;
  69
  70       if (t != NULL)
  71         SIZ (t) = 0;
  72       if (s != NULL)
  73         {
  74           SIZ (s) = ssize;
  75           PTR (s)[0] = 1;
  76         }
  77       return;
  78     }
  79
  80   TMP_MARK;
  81
  82   TMP_ALLOC_LIMBS_2 (tmp_ap, asize, tmp_bp, bsize);
  83   MPN_COPY (tmp_ap, PTR (a), asize);
  84   MPN_COPY (tmp_bp, PTR (b), bsize);
  85
  86   TMP_ALLOC_LIMBS_2 (tmp_gp, bsize, tmp_sp, bsize + 1);
  87
  88   gsize = mpn_gcdext (tmp_gp, tmp_sp, &tmp_ssize, tmp_ap, asize, tmp_bp, bsize);
  89
  90   ssize = ABS (tmp_ssize);
  91   tmp_ssize = SIZ (a) >= 0 ? tmp_ssize : -tmp_ssize;
  92
  93   if (t != NULL)
  94     {
  95       mpz_t x;
  96       __mpz_struct gtmp, stmp;
  97
  98       PTR (&gtmp) = tmp_gp;
  99       SIZ (&gtmp) = gsize;
 100
 101       PTR (&stmp) = tmp_sp;
 102       SIZ (&stmp) = tmp_ssize;
 103
 104       MPZ_TMP_INIT (x, ssize + asize + 1);
 105       mpz_mul (x, &stmp, a);
 106       mpz_sub (x, &gtmp, x);
 107       mpz_divexact (t, x, b);
 108     }
 109
 110   if (s != NULL)
 111     {
 112       mp_ptr sp;
 113
 114       sp = MPZ_REALLOC (s, ssize);
 115       MPN_COPY (sp, tmp_sp, ssize);
 116       SIZ (s) = tmp_ssize;
 117     }
 118
 119   gp = MPZ_REALLOC (g, gsize);
 120   MPN_COPY (gp, tmp_gp, gsize);
 121   SIZ (g) = gsize;
 122
 123   TMP_FREE;
 124 }