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
20mpi_limb_t
21mpihelp_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}
49