]>
Commit | Line | Data |
---|---|---|
cdec9cb5 DK |
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 | ||
41 | mpi_limb_t | |
42 | mpihelp_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 | } |