| Dmitry Kasatkin | 7e8dec9 | 2011-11-07 15:16:37 +0200 | [diff] [blame] | 1 | /* mpi-gcd.c - MPI functions |
| 2 | * Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc. |
| 3 | * |
| 4 | * This file is part of GnuPG. |
| 5 | * |
| 6 | * GnuPG is free software; you can redistribute it and/or modify |
| 7 | * it under the terms of the GNU General Public License as published by |
| 8 | * the Free Software Foundation; either version 2 of the License, or |
| 9 | * (at your option) any later version. |
| 10 | * |
| 11 | * GnuPG is distributed in the hope that it will be useful, |
| 12 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 13 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 14 | * GNU General Public License for more details. |
| 15 | * |
| 16 | * You should have received a copy of the GNU General Public License |
| 17 | * along with this program; if not, write to the Free Software |
| 18 | * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA |
| 19 | */ |
| 20 | |
| 21 | #include "mpi-internal.h" |
| 22 | |
| 23 | /**************** |
| 24 | * Find the greatest common divisor G of A and B. |
| 25 | * Return: true if this 1, false in all other cases |
| 26 | */ |
| 27 | int mpi_gcd(MPI g, const MPI xa, const MPI xb) |
| 28 | { |
| 29 | MPI a = NULL, b = NULL; |
| 30 | |
| 31 | if (mpi_copy(&a, xa) < 0) |
| 32 | goto nomem; |
| 33 | |
| 34 | if (mpi_copy(&b, xb) < 0) |
| 35 | goto nomem; |
| 36 | |
| 37 | /* TAOCP Vol II, 4.5.2, Algorithm A */ |
| 38 | a->sign = 0; |
| 39 | b->sign = 0; |
| 40 | while (mpi_cmp_ui(b, 0)) { |
| 41 | if (mpi_fdiv_r(g, a, b) < 0) /* g used as temorary variable */ |
| 42 | goto nomem; |
| 43 | if (mpi_set(a, b) < 0) |
| 44 | goto nomem; |
| 45 | if (mpi_set(b, g) < 0) |
| 46 | goto nomem; |
| 47 | } |
| 48 | if (mpi_set(g, a) < 0) |
| 49 | goto nomem; |
| 50 | |
| 51 | mpi_free(a); |
| 52 | mpi_free(b); |
| 53 | return !mpi_cmp_ui(g, 1); |
| 54 | |
| 55 | nomem: |
| 56 | mpi_free(a); |
| 57 | mpi_free(b); |
| 58 | return -ENOMEM; |
| 59 | } |