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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