51 lines
1.5 KiB
C
51 lines
1.5 KiB
C
|
// SPDX-License-Identifier: GPL-2.0-or-later
|
||
|
|
/* mpih-rshift.c - MPI helper functions
|
||
|
|
* Copyright (C) 1994, 1996, 1998, 1999,
|
||
|
|
* 2000, 2001 Free Software Foundation, Inc.
|
||
|
|
*
|
||
|
|
* This file is part of GNUPG
|
||
|
|
*
|
||
|
|
* Note: This code is heavily based on the GNU MP Library.
|
||
|
|
* Actually it's the same code with only minor changes in the
|
||
|
|
* way the data is stored; this is to support the abstraction
|
||
|
|
* of an optional secure memory allocation which may be used
|
||
|
|
* to avoid revealing of sensitive data due to paging etc.
|
||
|
|
* The GNU MP Library itself is published under the LGPL;
|
||
|
|
* however I decided to publish this code under the plain GPL.
|
||
|
|
*/
|
||
|
|
|
||
|
|
#include "mpi-internal.h"
|
||
|
|
|
||
|
|
/* Shift U (pointed to by UP and USIZE limbs long) CNT bits to the right
|
||
|
|
* and store the USIZE least significant limbs of the result at WP.
|
||
|
|
* The bits shifted out to the right are returned.
|
||
|
|
*
|
||
|
|
* Argument constraints:
|
||
|
|
* 1. 0 < CNT < BITS_PER_MP_LIMB
|
||
|
|
* 2. If the result is to be written over the input, WP must be <= UP.
|
||
|
|
*/
|
||
|
|
|
||
|
|
mpi_limb_t
|
||
|
|
mpihelp_rshift(mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize, unsigned cnt)
|
||
|
|
{
|
||
|
|
mpi_limb_t high_limb, low_limb;
|
||
|
|
unsigned sh_1, sh_2;
|
||
|
|
mpi_size_t i;
|
||
|
|
mpi_limb_t retval;
|
||
|
|
|
||
|
|
sh_1 = cnt;
|
||
|
|
wp -= 1;
|
||
|
|
sh_2 = BITS_PER_MPI_LIMB - sh_1;
|
||
|
|
high_limb = up[0];
|
||
|
|
retval = high_limb << sh_2;
|
||
|
|
low_limb = high_limb;
|
||
|
|
for (i = 1; i < usize; i++) {
|
||
|
|
high_limb = up[i];
|
||
|
|
wp[i] = (low_limb >> sh_1) | (high_limb << sh_2);
|
||
|
|
low_limb = high_limb;
|
||
|
|
}
|
||
|
|
wp[i] = low_limb >> sh_1;
|
||
|
|
|
||
|
|
return retval;
|
||
|
|
}
|