1 /* mpihelp-add_1.c - MPI helper functions
2 * Copyright (C) 1994, 1996, 1997, 1998,
3 * 2000 Free Software Foundation, Inc.
4 *
5 * This file is part of GnuPG.
6 *
7 * GnuPG is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License as published by
9 * the Free Software Foundation; either version 2 of the License, or
10 * (at your option) any later version.
11 *
12 * GnuPG is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 * GNU General Public License for more details.
16 *
17 * You should have received a copy of the GNU General Public License
18 * along with this program; if not, write to the Free Software
19 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
20 *
21 * Note: This code is heavily based on the GNU MP Library.
22 * Actually it's the same code with only minor changes in the
23 * way the data is stored; this is to support the abstraction
24 * of an optional secure memory allocation which may be used
25 * to avoid revealing of sensitive data due to paging etc.
26 * The GNU MP Library itself is published under the LGPL;
27 * however I decided to publish this code under the plain GPL.
28 */
29
30 #include "mpi-internal.h"
31 #include "longlong.h"
32
33 mpi_limb_t
mpihelp_add_n(mpi_ptr_t res_ptr,mpi_ptr_t s1_ptr,mpi_ptr_t s2_ptr,mpi_size_t size)34 mpihelp_add_n(mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
35 mpi_ptr_t s2_ptr, mpi_size_t size)
36 {
37 mpi_limb_t x, y, cy;
38 mpi_size_t j;
39
40 /* The loop counter and index J goes from -SIZE to -1. This way
41 the loop becomes faster. */
42 j = -size;
43
44 /* Offset the base pointers to compensate for the negative indices. */
45 s1_ptr -= j;
46 s2_ptr -= j;
47 res_ptr -= j;
48
49 cy = 0;
50 do {
51 y = s2_ptr[j];
52 x = s1_ptr[j];
53 y += cy; /* add previous carry to one addend */
54 cy = y < cy; /* get out carry from that addition */
55 y += x; /* add other addend */
56 cy += y < x; /* get out carry from that add, combine */
57 res_ptr[j] = y;
58 } while (++j);
59
60 return cy;
61 }
62