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, 1994, 1995, 1996, 1997, 2000, 2001, 2005 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 the GNU Lesser General Public License as published by 11 the Free Software Foundation; either version 3 of the License, or (at your 12 option) any later version. 13 14 The GNU MP Library is distributed in the hope that it will be useful, but 15 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 16 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 17 License for more details. 18 19 You should have received a copy of the GNU Lesser General Public License 20 along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */ 21 22 #include <stdio.h> /* for NULL */ 23 #include "gmp.h" 24 #include "gmp-impl.h" 25 26 void 27 mpz_gcdext (mpz_ptr g, mpz_ptr s, mpz_ptr t, mpz_srcptr a, mpz_srcptr b) 28 { 29 mp_size_t asize, bsize, usize, vsize; 30 mp_srcptr ap, bp; 31 mp_ptr up, vp; 32 mp_size_t gsize, ssize, tmp_ssize; 33 mp_ptr gp, sp, tmp_gp, tmp_sp; 34 mpz_srcptr u, v; 35 mpz_ptr ss, tt; 36 __mpz_struct stmp, gtmp; 37 TMP_DECL; 38 39 TMP_MARK; 40 41 /* mpn_gcdext requires that U >= V. Therefore, we often have to swap U and 42 V. This in turn leads to a lot of complications. The computed cofactor 43 will be the wrong one, so we have to fix that up at the end. */ 44 45 asize = ABS (SIZ (a)); 46 bsize = ABS (SIZ (b)); 47 ap = PTR (a); 48 bp = PTR (b); 49 if (asize > bsize || (asize == bsize && mpn_cmp (ap, bp, asize) > 0)) 50 { 51 usize = asize; 52 vsize = bsize; 53 up = TMP_ALLOC_LIMBS (usize + 1); 54 vp = TMP_ALLOC_LIMBS (vsize + 1); 55 MPN_COPY (up, ap, usize); 56 MPN_COPY (vp, bp, vsize); 57 u = a; 58 v = b; 59 ss = s; 60 tt = t; 61 } 62 else 63 { 64 usize = bsize; 65 vsize = asize; 66 up = TMP_ALLOC_LIMBS (usize + 1); 67 vp = TMP_ALLOC_LIMBS (vsize + 1); 68 MPN_COPY (up, bp, usize); 69 MPN_COPY (vp, ap, vsize); 70 u = b; 71 v = a; 72 ss = t; 73 tt = s; 74 } 75 76 tmp_gp = TMP_ALLOC_LIMBS (usize + 1); 77 tmp_sp = TMP_ALLOC_LIMBS (usize + 1); 78 79 if (vsize == 0) 80 { 81 tmp_sp[0] = 1; 82 tmp_ssize = 1; 83 MPN_COPY (tmp_gp, up, usize); 84 gsize = usize; 85 } 86 else 87 gsize = mpn_gcdext (tmp_gp, tmp_sp, &tmp_ssize, up, usize, vp, vsize); 88 ssize = ABS (tmp_ssize); 89 90 PTR (>mp) = tmp_gp; 91 SIZ (>mp) = gsize; 92 93 PTR (&stmp) = tmp_sp; 94 SIZ (&stmp) = (tmp_ssize ^ SIZ (u)) >= 0 ? ssize : -ssize; 95 96 if (tt != NULL) 97 { 98 if (SIZ (v) == 0) 99 SIZ (tt) = 0; 100 else 101 { 102 mpz_t x; 103 MPZ_TMP_INIT (x, ssize + usize + 1); 104 mpz_mul (x, &stmp, u); 105 mpz_sub (x, >mp, x); 106 mpz_tdiv_q (tt, x, v); 107 } 108 } 109 110 if (ss != NULL) 111 { 112 if (ALLOC (ss) < ssize) 113 _mpz_realloc (ss, ssize); 114 sp = PTR (ss); 115 MPN_COPY (sp, tmp_sp, ssize); 116 SIZ (ss) = SIZ (&stmp); 117 } 118 119 if (ALLOC (g) < gsize) 120 _mpz_realloc (g, gsize); 121 gp = PTR (g); 122 MPN_COPY (gp, tmp_gp, gsize); 123 SIZ (g) = gsize; 124 125 TMP_FREE; 126 } 127