1 // SPDX-License-Identifier: GPL-2.0-or-later 1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* mpih-rshift.c - MPI helper functions 2 /* mpih-rshift.c - MPI helper functions
3 * Copyright (C) 1994, 1996, 1998, 1999, 3 * Copyright (C) 1994, 1996, 1998, 1999,
4 * 2000, 2001 Free Software Foun 4 * 2000, 2001 Free Software Foundation, Inc.
5 * 5 *
6 * This file is part of GNUPG 6 * This file is part of GNUPG
7 * 7 *
8 * Note: This code is heavily based on the GNU 8 * Note: This code is heavily based on the GNU MP Library.
9 * Actually it's the same code with only 9 * Actually it's the same code with only minor changes in the
10 * way the data is stored; this is to su 10 * way the data is stored; this is to support the abstraction
11 * of an optional secure memory allocati 11 * of an optional secure memory allocation which may be used
12 * to avoid revealing of sensitive data 12 * to avoid revealing of sensitive data due to paging etc.
13 * The GNU MP Library itself is publishe 13 * The GNU MP Library itself is published under the LGPL;
14 * however I decided to publish this cod 14 * however I decided to publish this code under the plain GPL.
15 */ 15 */
16 16
17 #include "mpi-internal.h" 17 #include "mpi-internal.h"
18 18
19 /* Shift U (pointed to by UP and USIZE limbs l 19 /* Shift U (pointed to by UP and USIZE limbs long) CNT bits to the right
20 * and store the USIZE least significant limbs 20 * and store the USIZE least significant limbs of the result at WP.
21 * The bits shifted out to the right are retur 21 * The bits shifted out to the right are returned.
22 * 22 *
23 * Argument constraints: 23 * Argument constraints:
24 * 1. 0 < CNT < BITS_PER_MP_LIMB 24 * 1. 0 < CNT < BITS_PER_MP_LIMB
25 * 2. If the result is to be written over the 25 * 2. If the result is to be written over the input, WP must be <= UP.
26 */ 26 */
27 27
28 mpi_limb_t 28 mpi_limb_t
29 mpihelp_rshift(mpi_ptr_t wp, mpi_ptr_t up, mpi 29 mpihelp_rshift(mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize, unsigned cnt)
30 { 30 {
31 mpi_limb_t high_limb, low_limb; 31 mpi_limb_t high_limb, low_limb;
32 unsigned sh_1, sh_2; 32 unsigned sh_1, sh_2;
33 mpi_size_t i; 33 mpi_size_t i;
34 mpi_limb_t retval; 34 mpi_limb_t retval;
35 35
36 sh_1 = cnt; 36 sh_1 = cnt;
37 wp -= 1; 37 wp -= 1;
38 sh_2 = BITS_PER_MPI_LIMB - sh_1; 38 sh_2 = BITS_PER_MPI_LIMB - sh_1;
39 high_limb = up[0]; 39 high_limb = up[0];
40 retval = high_limb << sh_2; 40 retval = high_limb << sh_2;
41 low_limb = high_limb; 41 low_limb = high_limb;
42 for (i = 1; i < usize; i++) { 42 for (i = 1; i < usize; i++) {
43 high_limb = up[i]; 43 high_limb = up[i];
44 wp[i] = (low_limb >> sh_1) | ( 44 wp[i] = (low_limb >> sh_1) | (high_limb << sh_2);
45 low_limb = high_limb; 45 low_limb = high_limb;
46 } 46 }
47 wp[i] = low_limb >> sh_1; 47 wp[i] = low_limb >> sh_1;
48 48
49 return retval; 49 return retval;
50 } 50 }
51 51
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