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Diffstat (limited to 'mpi/mpi-inv.c')
| -rw-r--r-- | mpi/mpi-inv.c | 127 |
1 files changed, 127 insertions, 0 deletions
diff --git a/mpi/mpi-inv.c b/mpi/mpi-inv.c new file mode 100644 index 000000000..acde6055a --- /dev/null +++ b/mpi/mpi-inv.c @@ -0,0 +1,127 @@ +/* mpi-inv.c - MPI functions + * Copyright (c) 1997 by Werner Koch (dd9jn) + * + * This file is part of G10. + * + * G10 is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * G10 is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA + */ + +#include <config.h> +#include <stdio.h> +#include <stdlib.h> +#include "mpi-internal.h" + +/**************** + * Calculate the multiplicative inverse X of U mod V + * That is: Find the solution for + * 1 = (u*x) mod v + * This has only a unique solution if U and V are relatively prime. + * Returns 0 if a solution was found. + */ +int +mpi_inv_mod( MPI x, MPI u, MPI v ) +{ + #if 0 + /* Extended Euclid's algorithm (See TAOPC Vol II, 4.52. Alg X) */ + MPI u1, u2, u3, v1, v2, v3, q, t1, t2, t3; + + u1 = mpi_alloc_set_ui(1); + u2 = mpi_alloc_set_ui(0); + u3 = mpi_copy(u); + v1 = mpi_alloc_set_ui(0); + v2 = mpi_alloc_set_ui(1); + v3 = mpi_copy(v); + q = mpi_alloc( mpi_get_nlimbs(u) ); + t1 = mpi_alloc( mpi_get_nlimbs(u) ); + t2 = mpi_alloc( mpi_get_nlimbs(u) ); + t3 = mpi_alloc( mpi_get_nlimbs(u) ); + while( mpi_cmp_ui( v3, 0 ) ) { + /*log_debug("----------------------\n"); + log_mpidump("q =", u1); + log_mpidump("u1=", u1); + log_mpidump("u2=", u2); + log_mpidump("u3=", u3); + log_mpidump("v1=", v1); + log_mpidump("v2=", v2); + log_mpidump("v3=", v3); */ + mpi_fdiv_q( q, u3, v3 ); + mpi_mul(t1, v1, q); mpi_mul(t2, v2, q); mpi_mul(t3, v3, q); + mpi_sub(t1, u1, t1); mpi_sub(t2, u2, t2); mpi_sub(t3, u3, t3); + + mpi_set(u1, v1); mpi_set(u2, v2); mpi_set(u3, v3); + mpi_set(v1, t1); mpi_set(v2, t2); mpi_set(v3, t3); + } + mpi_set(x, u3); + + mpi_free(u1); + mpi_free(u2); + mpi_free(u3); + mpi_free(v1); + mpi_free(v2); + mpi_free(v3); + mpi_free(q); + mpi_free(t1); + mpi_free(t2); + mpi_free(t3); + #endif + + /***************************** + * 1. Init: g0 = u g1 = v v0 = 0 v1 = 1 + * 2. Test: if g1 is 0 terminate. Result = v0 < 0: v0 + n + * else: v0 + * 3. Divide: div,rem = g0 / g1 + * t1 = v0 - div * v1 + * v0 = v1 + * v1 = t1 + * g0 = g1 + * g1 = rem + * continue with step 2. + */ + MPI g0, g1, v0, v1, div, rem, t1; + + g0 = mpi_copy(v); + g1 = mpi_copy(u); + v0 = mpi_alloc_set_ui( 0 ); + v1 = mpi_alloc_set_ui( 1 ); + div = mpi_alloc(mpi_get_nlimbs(v)); + rem = mpi_alloc(mpi_get_nlimbs(v)); + t1 = mpi_alloc(mpi_get_nlimbs(v)); + while( mpi_cmp_ui( g1, 0) ) { + mpi_fdiv_qr(div, rem, g0, g1); + mpi_mul(t1, div, v1); + mpi_sub(t1, v0, t1); + mpi_set(v0, v1); + mpi_set(v1, t1); + mpi_set(g0, g1); + mpi_set(g1, rem); + + } + if( mpi_cmp_ui( v0, 0) < 0 ) + mpi_add( x, v0, v); + else + mpi_set( x, v0); + + mpi_free(g0); + mpi_free(g1); + mpi_free(v0); + mpi_free(v1); + mpi_free(div); + mpi_free(rem); + mpi_free(t1); + return 0; +} + + + |