1/* mpi-lshift.c - MPI helper functions 2 * Copyright (C) 1994, 1996, 1998, 2001, 2002 Free Software Foundation, Inc. 3 * 4 * This file is part of Libgcrypt. 5 * 6 * Libgcrypt is free software; you can redistribute it and/or modify 7 * it under the terms of the GNU Lesser General Public License as 8 * published by the Free Software Foundation; either version 2.1 of 9 * the License, or (at your option) any later version. 10 * 11 * Libgcrypt is distributed in the hope that it will be useful, 12 * but WITHOUT ANY WARRANTY; without even the implied warranty of 13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 14 * GNU Lesser General Public License for more details. 15 * 16 * You should have received a copy of the GNU Lesser General Public 17 * License along with this program; if not, write to the Free Software 18 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA 19 * 20 * Note: This code is heavily based on the GNU MP Library. 21 * Actually it's the same code with only minor changes in the 22 * way the data is stored; this is to support the abstraction 23 * of an optional secure memory allocation which may be used 24 * to avoid revealing of sensitive data due to paging etc. 25 */ 26 27#include <config.h> 28#include <stdio.h> 29#include <stdlib.h> 30#include "mpi-internal.h" 31 32/* Shift U (pointed to by UP and USIZE digits long) CNT bits to the left 33 * and store the USIZE least significant digits of the result at WP. 34 * Return the bits shifted out from the most significant digit. 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 41mpi_limb_t 42_gcry_mpih_lshift( mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize, 43 unsigned int cnt) 44{ 45 mpi_limb_t high_limb, low_limb; 46 unsigned sh_1, sh_2; 47 mpi_size_t i; 48 mpi_limb_t retval; 49 50 sh_1 = cnt; 51 wp += 1; 52 sh_2 = BITS_PER_MPI_LIMB - sh_1; 53 i = usize - 1; 54 low_limb = up[i]; 55 retval = low_limb >> sh_2; 56 high_limb = low_limb; 57 while ( --i >= 0 ) 58 { 59 low_limb = up[i]; 60 wp[i] = (high_limb << sh_1) | (low_limb >> sh_2); 61 high_limb = low_limb; 62 } 63 wp[i] = high_limb << sh_1; 64 65 return retval; 66} 67 68 69