1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* mpihelp-add_1.c - MPI helper functions
3 * Copyright (C) 1994, 1996, 1997, 1998,
4 * 2000 Free Software Foundation, Inc.
5 *
6 * This file is part of GnuPG.
7 *
8 * Note: This code is heavily based on the GNU MP Library.
9 * Actually it's the same code with only minor changes in the
10 * way the data is stored; this is to support the abstraction
11 * of an optional secure memory allocation which may be used
12 * to avoid revealing of sensitive data due to paging etc.
13 * The GNU MP Library itself is published under the LGPL;
14 * however I decided to publish this code under the plain GPL.
15 */
16
17 #include "mpi-internal.h"
18 #include "longlong.h"
19
20 mpi_limb_t
21 mpihelp_add_n(mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
22 mpi_ptr_t s2_ptr, mpi_size_t size)
23 {
24 mpi_limb_t x, y, cy;
25 mpi_size_t j;
26
27 /* The loop counter and index J goes from -SIZE to -1. This way
28 the loop becomes faster. */
29 j = -size;
30
31 /* Offset the base pointers to compensate for the negative indices. */
32 s1_ptr -= j;
33 s2_ptr -= j;
34 res_ptr -= j;
35
36 cy = 0;
37 do {
38 y = s2_ptr[j];
39 x = s1_ptr[j];
40 y += cy; /* add previous carry to one addend */
41 cy = y < cy; /* get out carry from that addition */
42 y += x; /* add other addend */
43 cy += y < x; /* get out carry from that add, combine */
44 res_ptr[j] = y;
45 } while (++j);
46
47 return cy;
48 }