raw
mpi-genesis             1 /* mpihelp-add_1.c  -  MPI helper functions
mpi-genesis             2  * Copyright (C) 1994, 1996, 1997, 1998, 
mpi-genesis             3  *               2000 Free Software Foundation, Inc.
mpi-genesis             4  *
mpi-genesis             5  * This file is part of GnuPG.
mpi-genesis             6  *
mpi-genesis             7  * GnuPG is free software; you can redistribute it and/or modify
mpi-genesis             8  * it under the terms of the GNU General Public License as published by
mpi-genesis             9  * the Free Software Foundation; either version 3 of the License, or
mpi-genesis            10  * (at your option) any later version.
mpi-genesis            11  *
mpi-genesis            12  * GnuPG is distributed in the hope that it will be useful,
mpi-genesis            13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
mpi-genesis            14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
mpi-genesis            15  * GNU General Public License for more details.
mpi-genesis            16  *
mpi-genesis            17  * You should have received a copy of the GNU General Public License
mpi-genesis            18  * along with this program; if not, see <http://www.gnu.org/licenses/>.
mpi-genesis            19  *
mpi-genesis            20  * Note: This code is heavily based on the GNU MP Library.
mpi-genesis            21  *	 Actually it's the same code with only minor changes in the
mpi-genesis            22  *	 way the data is stored; this is to support the abstraction
mpi-genesis            23  *	 of an optional secure memory allocation which may be used
mpi-genesis            24  *	 to avoid revealing of sensitive data due to paging etc.
mpi-genesis            25  *	 The GNU MP Library itself is published under the LGPL;
mpi-genesis            26  *	 however I decided to publish this code under the plain GPL.
mpi-genesis            27  */
mpi-genesis            28 
mpi-genesis            29 #include <config.h>
mpi-genesis            30 #include <stdio.h>
mpi-genesis            31 #include <stdlib.h>
mpi-genesis            32 #include "mpi-internal.h"
mpi-genesis            33 #include "longlong.h"
mpi-genesis            34 
mpi-genesis            35 mpi_limb_t
mpi-genesis            36 mpihelp_add_n( mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
mpi-genesis            37 	       mpi_ptr_t s2_ptr, mpi_size_t size)
mpi-genesis            38 {
mpi-genesis            39     mpi_limb_t x, y, cy;
mpi-genesis            40     mpi_size_t j;
mpi-genesis            41 
mpi-genesis            42     /* The loop counter and index J goes from -SIZE to -1.  This way
mpi-genesis            43        the loop becomes faster.  */
mpi-genesis            44     j = -size;
mpi-genesis            45 
mpi-genesis            46     /* Offset the base pointers to compensate for the negative indices. */
mpi-genesis            47     s1_ptr -= j;
mpi-genesis            48     s2_ptr -= j;
mpi-genesis            49     res_ptr -= j;
mpi-genesis            50 
mpi-genesis            51     cy = 0;
mpi-genesis            52     do {
mpi-genesis            53 	y = s2_ptr[j];
mpi-genesis            54 	x = s1_ptr[j];
mpi-genesis            55 	y += cy;		  /* add previous carry to one addend */
mpi-genesis            56 	cy = y < cy;		  /* get out carry from that addition */
mpi-genesis            57 	y += x; 		  /* add other addend */
mpi-genesis            58 	cy += y < x;		  /* get out carry from that add, combine */
mpi-genesis            59 	res_ptr[j] = y;
mpi-genesis            60     } while( ++j );
mpi-genesis            61 
mpi-genesis            62     return cy;
mpi-genesis            63 }
mpi-genesis            64