| Dmitry Kasatkin | cdec9cb | 2011-08-31 14:05:16 +0300 | [diff] [blame^] | 1 | /* mpihelp-lshift.c - MPI helper functions |
| 2 | * Copyright (C) 1994, 1996, 1998, 2001 Free Software Foundation, Inc. |
| 3 | * |
| 4 | * This file is part of GnuPG. |
| 5 | * |
| 6 | * GnuPG is free software; you can redistribute it and/or modify |
| 7 | * it under the terms of the GNU General Public License as published by |
| 8 | * the Free Software Foundation; either version 2 of the License, or |
| 9 | * (at your option) any later version. |
| 10 | * |
| 11 | * GnuPG 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 General Public License for more details. |
| 15 | * |
| 16 | * You should have received a copy of the GNU General Public License |
| 17 | * 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 | * The GNU MP Library itself is published under the LGPL; |
| 26 | * however I decided to publish this code under the plain GPL. |
| 27 | */ |
| 28 | |
| 29 | #include "mpi-internal.h" |
| 30 | |
| 31 | /* Shift U (pointed to by UP and USIZE digits long) CNT bits to the left |
| 32 | * and store the USIZE least significant digits of the result at WP. |
| 33 | * Return the bits shifted out from the most significant digit. |
| 34 | * |
| 35 | * Argument constraints: |
| 36 | * 1. 0 < CNT < BITS_PER_MP_LIMB |
| 37 | * 2. If the result is to be written over the input, WP must be >= UP. |
| 38 | */ |
| 39 | |
| 40 | mpi_limb_t |
| 41 | mpihelp_lshift(mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize, unsigned int cnt) |
| 42 | { |
| 43 | mpi_limb_t high_limb, low_limb; |
| 44 | unsigned sh_1, sh_2; |
| 45 | mpi_size_t i; |
| 46 | mpi_limb_t retval; |
| 47 | |
| 48 | sh_1 = cnt; |
| 49 | wp += 1; |
| 50 | sh_2 = BITS_PER_MPI_LIMB - sh_1; |
| 51 | i = usize - 1; |
| 52 | low_limb = up[i]; |
| 53 | retval = low_limb >> sh_2; |
| 54 | high_limb = low_limb; |
| 55 | while (--i >= 0) { |
| 56 | low_limb = up[i]; |
| 57 | wp[i] = (high_limb << sh_1) | (low_limb >> sh_2); |
| 58 | high_limb = low_limb; |
| 59 | } |
| 60 | wp[i] = high_limb << sh_1; |
| 61 | |
| 62 | return retval; |
| 63 | } |