1/* mpih-rshift.c  -  MPI helper functions
 2 * Copyright (C) 1994, 1996, 1998, 1999,
 3 *               2000, 2001 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
32/* Shift U (pointed to by UP and USIZE limbs long) CNT bits to the right
33 * and store the USIZE least significant limbs of the result at WP.
34 * The bits shifted out to the right are returned.
35 *
36 * Argument constraints:
37 * 1. 0 < CNT < BITS_PER_MP_LIMB
38 * 2. If the result is to be written over the input, WP must be <= UP.
39 */
40
41mpi_limb_t
42mpihelp_rshift(mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize, unsigned cnt)
43{
44	mpi_limb_t high_limb, low_limb;
45	unsigned sh_1, sh_2;
46	mpi_size_t i;
47	mpi_limb_t retval;
48
49	sh_1 = cnt;
50	wp -= 1;
51	sh_2 = BITS_PER_MPI_LIMB - sh_1;
52	high_limb = up[0];
53	retval = high_limb << sh_2;
54	low_limb = high_limb;
55	for (i = 1; i < usize; i++) {
56		high_limb = up[i];
57		wp[i] = (low_limb >> sh_1) | (high_limb << sh_2);
58		low_limb = high_limb;
59	}
60	wp[i] = low_limb >> sh_1;
61
62	return retval;
63}

 1// SPDX-License-Identifier: GPL-2.0-or-later
 2/* mpih-rshift.c  -  MPI helper functions
 3 * Copyright (C) 1994, 1996, 1998, 1999,
 4 *               2000, 2001 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
19/* Shift U (pointed to by UP and USIZE limbs long) CNT bits to the right
20 * and store the USIZE least significant limbs of the result at WP.
21 * The bits shifted out to the right are returned.
22 *
23 * Argument constraints:
24 * 1. 0 < CNT < BITS_PER_MP_LIMB
25 * 2. If the result is to be written over the input, WP must be <= UP.
26 */
27
28mpi_limb_t
29mpihelp_rshift(mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize, unsigned cnt)
30{
31	mpi_limb_t high_limb, low_limb;
32	unsigned sh_1, sh_2;
33	mpi_size_t i;
34	mpi_limb_t retval;
35
36	sh_1 = cnt;
37	wp -= 1;
38	sh_2 = BITS_PER_MPI_LIMB - sh_1;
39	high_limb = up[0];
40	retval = high_limb << sh_2;
41	low_limb = high_limb;
42	for (i = 1; i < usize; i++) {
43		high_limb = up[i];
44		wp[i] = (low_limb >> sh_1) | (high_limb << sh_2);
45		low_limb = high_limb;
46	}
47	wp[i] = low_limb >> sh_1;
48
49	return retval;
50}