| /* mpih-rshift.c - MPI helper functions |
| * Copyright (C) 1994, 1996, 1998, 1999, |
| * 2000, 2001, 2002 Free Software Foundation, Inc. |
| * |
| * This file is part of Libgcrypt. |
| * |
| * Libgcrypt is free software; you can redistribute it and/or modify |
| * it under the terms of the GNU Lesser General Public License as |
| * published by the Free Software Foundation; either version 2.1 of |
| * the License, or (at your option) any later version. |
| * |
| * Libgcrypt 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 Lesser General Public License for more details. |
| * |
| * You should have received a copy of the GNU Lesser 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. |
| */ |
| |
| #include <config.h> |
| #include <stdio.h> |
| #include <stdlib.h> |
| #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 |
| _gcry_mpih_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; |
| } |
| |