64 lines
2.1 KiB
C
64 lines
2.1 KiB
C
/* mpihelp-lshift.c - MPI helper functions
|
|
* Copyright (C) 1994, 1996, 1998, 2001 Free Software Foundation, Inc.
|
|
*
|
|
* This file is part of GnuPG.
|
|
*
|
|
* GnuPG is free software; you can redistribute it and/or modify
|
|
* it under the terms of the GNU General Public License as published by
|
|
* the Free Software Foundation; either version 2 of the License, or
|
|
* (at your option) any later version.
|
|
*
|
|
* GnuPG is distributed in the hope that it will be useful,
|
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
* GNU General Public License for more details.
|
|
*
|
|
* You should have received a copy of the GNU General Public License
|
|
* along with this program; if not, write to the Free Software
|
|
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
|
|
*
|
|
* 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 digits long) CNT bits to the left
|
|
* and store the USIZE least significant digits of the result at WP.
|
|
* Return the bits shifted out from the most significant digit.
|
|
*
|
|
* 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_lshift(mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize, unsigned int 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;
|
|
i = usize - 1;
|
|
low_limb = up[i];
|
|
retval = low_limb >> sh_2;
|
|
high_limb = low_limb;
|
|
while (--i >= 0) {
|
|
low_limb = up[i];
|
|
wp[i] = (high_limb << sh_1) | (low_limb >> sh_2);
|
|
high_limb = low_limb;
|
|
}
|
|
wp[i] = high_limb << sh_1;
|
|
|
|
return retval;
|
|
}
|