1/* mpihelp-add_2.c  -  MPI helper functions
 2 * Copyright (C) 1994, 1996, 1997, 1998, 2001 Free Software Foundation, Inc.
 3 *
 4 * This file is part of GnuPG.
 5 *
 6 * GnuPG is free software; you can redistribute it and/or modify
 7 * it under the terms of the GNU General Public License as published by
 8 * the Free Software Foundation; either version 2 of the License, or
 9 * (at your option) any later version.
10 *
11 * GnuPG is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14 * GNU General Public License for more details.
15 *
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, write to the Free Software
18 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
19 *
20 * Note: This code is heavily based on the GNU MP Library.
21 *	 Actually it's the same code with only minor changes in the
22 *	 way the data is stored; this is to support the abstraction
23 *	 of an optional secure memory allocation which may be used
24 *	 to avoid revealing of sensitive data due to paging etc.
25 *	 The GNU MP Library itself is published under the LGPL;
26 *	 however I decided to publish this code under the plain GPL.
27 */
28
29#include "mpi-internal.h"
30#include "longlong.h"
31
32mpi_limb_t
33mpihelp_sub_n(mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
34	      mpi_ptr_t s2_ptr, mpi_size_t size)
35{
36	mpi_limb_t x, y, cy;
37	mpi_size_t j;
38
39	/* The loop counter and index J goes from -SIZE to -1.  This way
40	   the loop becomes faster.  */
41	j = -size;
42
43	/* Offset the base pointers to compensate for the negative indices.  */
44	s1_ptr -= j;
45	s2_ptr -= j;
46	res_ptr -= j;
47
48	cy = 0;
49	do {
50		y = s2_ptr[j];
51		x = s1_ptr[j];
52		y += cy;	/* add previous carry to subtrahend */
53		cy = y < cy;	/* get out carry from that addition */
54		y = x - y;	/* main subtract */
55		cy += y > x;	/* get out carry from the subtract, combine */
56		res_ptr[j] = y;
57	} while (++j);
58
59	return cy;
60}

 1// SPDX-License-Identifier: GPL-2.0-or-later
 2/* mpihelp-add_2.c  -  MPI helper functions
 3 * Copyright (C) 1994, 1996, 1997, 1998, 2001 Free Software Foundation, Inc.
 4 *
 5 * This file is part of GnuPG.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 6 *
 7 * Note: This code is heavily based on the GNU MP Library.
 8 *	 Actually it's the same code with only minor changes in the
 9 *	 way the data is stored; this is to support the abstraction
10 *	 of an optional secure memory allocation which may be used
11 *	 to avoid revealing of sensitive data due to paging etc.
12 *	 The GNU MP Library itself is published under the LGPL;
13 *	 however I decided to publish this code under the plain GPL.
14 */
15
16#include "mpi-internal.h"
17#include "longlong.h"
18
19mpi_limb_t
20mpihelp_sub_n(mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
21	      mpi_ptr_t s2_ptr, mpi_size_t size)
22{
23	mpi_limb_t x, y, cy;
24	mpi_size_t j;
25
26	/* The loop counter and index J goes from -SIZE to -1.  This way
27	   the loop becomes faster.  */
28	j = -size;
29
30	/* Offset the base pointers to compensate for the negative indices.  */
31	s1_ptr -= j;
32	s2_ptr -= j;
33	res_ptr -= j;
34
35	cy = 0;
36	do {
37		y = s2_ptr[j];
38		x = s1_ptr[j];
39		y += cy;	/* add previous carry to subtrahend */
40		cy = y < cy;	/* get out carry from that addition */
41		y = x - y;	/* main subtract */
42		cy += y > x;	/* get out carry from the subtract, combine */
43		res_ptr[j] = y;
44	} while (++j);
45
46	return cy;
47}