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mpi-genesis             1 /* mpihelp-mul_3.c  -  MPI helper functions
mpi-genesis 2 * Copyright (C) 1994, 1996, 1997, 1998, 2001 Free Software Foundation, Inc.
mpi-genesis 3 *
mpi-genesis 4 * This file is part of GnuPG.
mpi-genesis 5 *
mpi-genesis 6 * GnuPG is free software; you can redistribute it and/or modify
mpi-genesis 7 * it under the terms of the GNU General Public License as published by
mpi-genesis 8 * the Free Software Foundation; either version 3 of the License, or
mpi-genesis 9 * (at your option) any later version.
mpi-genesis 10 *
mpi-genesis 11 * GnuPG is distributed in the hope that it will be useful,
mpi-genesis 12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
mpi-genesis 13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
mpi-genesis 14 * GNU General Public License for more details.
mpi-genesis 15 *
mpi-genesis 16 * You should have received a copy of the GNU General Public License
mpi-genesis 17 * along with this program; if not, see <http://www.gnu.org/licenses/>.
mpi-genesis 18 *
mpi-genesis 19 * Note: This code is heavily based on the GNU MP Library.
mpi-genesis 20 * Actually it's the same code with only minor changes in the
mpi-genesis 21 * way the data is stored; this is to support the abstraction
mpi-genesis 22 * of an optional secure memory allocation which may be used
mpi-genesis 23 * to avoid revealing of sensitive data due to paging etc.
mpi-genesis 24 * The GNU MP Library itself is published under the LGPL;
mpi-genesis 25 * however I decided to publish this code under the plain GPL.
mpi-genesis 26 */
mpi-genesis 27
mpi-genesis 28 #include <config.h>
mpi-genesis 29 #include <stdio.h>
mpi-genesis 30 #include <stdlib.h>
mpi-genesis 31 #include "mpi-internal.h"
mpi-genesis 32 #include "longlong.h"
mpi-genesis 33
mpi-genesis 34
mpi-genesis 35 mpi_limb_t
mpi-genesis 36 mpihelp_submul_1( mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
mpi-genesis 37 mpi_size_t s1_size, mpi_limb_t s2_limb)
mpi-genesis 38 {
mpi-genesis 39 mpi_limb_t cy_limb;
mpi-genesis 40 mpi_size_t j;
mpi-genesis 41 mpi_limb_t prod_high, prod_low;
mpi-genesis 42 mpi_limb_t x;
mpi-genesis 43
mpi-genesis 44 /* The loop counter and index J goes from -SIZE to -1. This way
mpi-genesis 45 * the loop becomes faster. */
mpi-genesis 46 j = -s1_size;
mpi-genesis 47 res_ptr -= j;
mpi-genesis 48 s1_ptr -= j;
mpi-genesis 49
mpi-genesis 50 cy_limb = 0;
mpi-genesis 51 do {
mpi-genesis 52 umul_ppmm( prod_high, prod_low, s1_ptr[j], s2_limb);
mpi-genesis 53
mpi-genesis 54 prod_low += cy_limb;
mpi-genesis 55 cy_limb = (prod_low < cy_limb?1:0) + prod_high;
mpi-genesis 56
mpi-genesis 57 x = res_ptr[j];
mpi-genesis 58 prod_low = x - prod_low;
mpi-genesis 59 cy_limb += prod_low > x?1:0;
mpi-genesis 60 res_ptr[j] = prod_low;
mpi-genesis 61 } while( ++j );
mpi-genesis 62
mpi-genesis 63 return cy_limb;
mpi-genesis 64 }
mpi-genesis 65
mpi-genesis 66