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63 lines
2.1 KiB
63 lines
2.1 KiB
/* mpih-rshift.c - MPI helper functions |
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* Copyright (C) 1994, 1996, 1998, 1999, |
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* 2000, 2001 Free Software Foundation, Inc. |
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* |
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* This file is part of GNUPG |
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* |
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* GNUPG is free software; you can redistribute it and/or modify |
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* it under the terms of the GNU General Public License as published by |
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* the Free Software Foundation; either version 2 of the License, or |
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* (at your option) any later version. |
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* |
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* GNUPG is distributed in the hope that it will be useful, |
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* but WITHOUT ANY WARRANTY; without even the implied warranty of |
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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* GNU General Public License for more details. |
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* |
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* You should have received a copy of the GNU General Public License |
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* along with this program; if not, write to the Free Software |
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA |
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* |
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* Note: This code is heavily based on the GNU MP Library. |
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* Actually it's the same code with only minor changes in the |
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* way the data is stored; this is to support the abstraction |
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* of an optional secure memory allocation which may be used |
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* to avoid revealing of sensitive data due to paging etc. |
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* The GNU MP Library itself is published under the LGPL; |
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* however I decided to publish this code under the plain GPL. |
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*/ |
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#include "mpi-internal.h" |
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/* Shift U (pointed to by UP and USIZE limbs long) CNT bits to the right |
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* and store the USIZE least significant limbs of the result at WP. |
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* The bits shifted out to the right are returned. |
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* |
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* Argument constraints: |
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* 1. 0 < CNT < BITS_PER_MP_LIMB |
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* 2. If the result is to be written over the input, WP must be <= UP. |
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*/ |
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mpi_limb_t |
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mpihelp_rshift(mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize, unsigned cnt) |
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{ |
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mpi_limb_t high_limb, low_limb; |
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unsigned sh_1, sh_2; |
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mpi_size_t i; |
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mpi_limb_t retval; |
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sh_1 = cnt; |
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wp -= 1; |
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sh_2 = BITS_PER_MPI_LIMB - sh_1; |
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high_limb = up[0]; |
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retval = high_limb << sh_2; |
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low_limb = high_limb; |
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for (i = 1; i < usize; i++) { |
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high_limb = up[i]; |
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wp[i] = (low_limb >> sh_1) | (high_limb << sh_2); |
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low_limb = high_limb; |
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} |
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wp[i] = low_limb >> sh_1; |
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return retval; |
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}
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