51 lines
1.5 KiB
C
51 lines
1.5 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/* 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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* 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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