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git.proxmox.com Git - mirror_ubuntu-eoan-kernel.git/blob - lib/mpi/generic_mpih-rshift.c
1 /* mpih-rshift.c - MPI helper functions
2 * Copyright (C) 1994, 1996, 1998, 1999,
3 * 2000, 2001 Free Software Foundation, Inc.
5 * This file is part of GNUPG
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.
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.
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
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.
30 #include "mpi-internal.h"
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.
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.
42 mpihelp_rshift(mpi_ptr_t wp
, mpi_ptr_t up
, mpi_size_t usize
, unsigned cnt
)
44 mpi_limb_t high_limb
, low_limb
;
51 sh_2
= BITS_PER_MPI_LIMB
- sh_1
;
53 retval
= high_limb
<< sh_2
;
55 for (i
= 1; i
< usize
; i
++) {
57 wp
[i
] = (low_limb
>> sh_1
) | (high_limb
<< sh_2
);
60 wp
[i
] = low_limb
>> sh_1
;