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

   1 /* mpz/gcd.c:   Calculate the greatest common divisor of two integers.
   2
   3 Copyright 1991, 1993, 1994, 1996, 2000-2002, 2005, 2010 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 either:
  10
  11   * the GNU Lesser General Public License as published by the Free
  12     Software Foundation; either version 3 of the License, or (at your
  13     option) any later version.
  14
  15 or
  16
  17   * the GNU General Public License as published by the Free Software
  18     Foundation; either version 2 of the License, or (at your option) any
  19     later version.
  20
  21 or both in parallel, as here.
  22
  23 The GNU MP Library is distributed in the hope that it will be useful, but
  24 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  25 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  26 for more details.
  27
  28 You should have received copies of the GNU General Public License and the
  29 GNU Lesser General Public License along with the GNU MP Library.  If not,
  30 see https://www.gnu.org/licenses/.  */
  31
  32 #include "gmp.h"
  33 #include "gmp-impl.h"
  34 #include "longlong.h"
  35
  36
  37 void
  38 mpz_gcd (mpz_ptr g, mpz_srcptr u, mpz_srcptr v)
  39 {
  40   unsigned long int g_zero_bits, u_zero_bits, v_zero_bits;
  41   mp_size_t g_zero_limbs, u_zero_limbs, v_zero_limbs;
  42   mp_ptr tp;
  43   mp_ptr up;
  44   mp_size_t usize;
  45   mp_ptr vp;
  46   mp_size_t vsize;
  47   mp_size_t gsize;
  48   TMP_DECL;
  49
  50   up = PTR(u);
  51   usize = ABSIZ (u);
  52   vp = PTR(v);
  53   vsize = ABSIZ (v);
  54   /* GCD(0, V) == V.  */
  55   if (usize == 0)
  56     {
  57       SIZ (g) = vsize;
  58       if (g == v)
  59         return;
  60       MPZ_REALLOC (g, vsize);
  61       MPN_COPY (PTR (g), vp, vsize);
  62       return;
  63     }
  64
  65   /* GCD(U, 0) == U.  */
  66   if (vsize == 0)
  67     {
  68       SIZ (g) = usize;
  69       if (g == u)
  70         return;
  71       MPZ_REALLOC (g, usize);
  72       MPN_COPY (PTR (g), up, usize);
  73       return;
  74     }
  75
  76   if (usize == 1)
  77     {
  78       SIZ (g) = 1;
  79       PTR (g)[0] = mpn_gcd_1 (vp, vsize, up[0]);
  80       return;
  81     }
  82
  83   if (vsize == 1)
  84     {
  85       SIZ(g) = 1;
  86       PTR (g)[0] = mpn_gcd_1 (up, usize, vp[0]);
  87       return;
  88     }
  89
  90   TMP_MARK;
  91
  92   /*  Eliminate low zero bits from U and V and move to temporary storage.  */
  93   while (*up == 0)
  94     up++;
  95   u_zero_limbs = up - PTR(u);
  96   usize -= u_zero_limbs;
  97   count_trailing_zeros (u_zero_bits, *up);
  98   tp = up;
  99   up = TMP_ALLOC_LIMBS (usize);
 100   if (u_zero_bits != 0)
 101     {
 102       mpn_rshift (up, tp, usize, u_zero_bits);
 103       usize -= up[usize - 1] == 0;
 104     }
 105   else
 106     MPN_COPY (up, tp, usize);
 107
 108   while (*vp == 0)
 109     vp++;
 110   v_zero_limbs = vp - PTR (v);
 111   vsize -= v_zero_limbs;
 112   count_trailing_zeros (v_zero_bits, *vp);
 113   tp = vp;
 114   vp = TMP_ALLOC_LIMBS (vsize);
 115   if (v_zero_bits != 0)
 116     {
 117       mpn_rshift (vp, tp, vsize, v_zero_bits);
 118       vsize -= vp[vsize - 1] == 0;
 119     }
 120   else
 121     MPN_COPY (vp, tp, vsize);
 122
 123   if (u_zero_limbs > v_zero_limbs)
 124     {
 125       g_zero_limbs = v_zero_limbs;
 126       g_zero_bits = v_zero_bits;
 127     }
 128   else if (u_zero_limbs < v_zero_limbs)
 129     {
 130       g_zero_limbs = u_zero_limbs;
 131       g_zero_bits = u_zero_bits;
 132     }
 133   else  /*  Equal.  */
 134     {
 135       g_zero_limbs = u_zero_limbs;
 136       g_zero_bits = MIN (u_zero_bits, v_zero_bits);
 137     }
 138
 139   /*  Call mpn_gcd.  The 2nd argument must not have more bits than the 1st.  */
 140   vsize = (usize < vsize || (usize == vsize && up[usize-1] < vp[vsize-1]))
 141     ? mpn_gcd (vp, vp, vsize, up, usize)
 142     : mpn_gcd (vp, up, usize, vp, vsize);
 143
 144   /*  Here G <-- V << (g_zero_limbs*GMP_LIMB_BITS + g_zero_bits).  */
 145   gsize = vsize + g_zero_limbs;
 146   if (g_zero_bits != 0)
 147     {
 148       mp_limb_t cy_limb;
 149       gsize += (vp[vsize - 1] >> (GMP_NUMB_BITS - g_zero_bits)) != 0;
 150       MPZ_REALLOC (g, gsize);
 151       MPN_ZERO (PTR (g), g_zero_limbs);
 152
 153       tp = PTR(g) + g_zero_limbs;
 154       cy_limb = mpn_lshift (tp, vp, vsize, g_zero_bits);
 155       if (cy_limb != 0)
 156         tp[vsize] = cy_limb;
 157     }
 158   else
 159     {
 160       MPZ_REALLOC (g, gsize);
 161       MPN_ZERO (PTR (g), g_zero_limbs);
 162       MPN_COPY (PTR (g) + g_zero_limbs, vp, vsize);
 163     }
 164
 165   SIZ (g) = gsize;
 166   TMP_FREE;
 167 }