51 lines
1.5 KiB
C
51 lines
1.5 KiB
C
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// SPDX-License-Identifier: GPL-2.0-or-later
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/* mpihelp-lshift.c - MPI helper functions
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* Copyright (C) 1994, 1996, 1998, 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 digits long) CNT bits to the left
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* and store the USIZE least significant digits of the result at WP.
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* Return the bits shifted out from the most significant digit.
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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_lshift(mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize, unsigned int 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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i = usize - 1;
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low_limb = up[i];
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retval = low_limb >> sh_2;
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high_limb = low_limb;
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while (--i >= 0) {
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low_limb = up[i];
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wp[i] = (high_limb << sh_1) | (low_limb >> sh_2);
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high_limb = low_limb;
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}
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wp[i] = high_limb << sh_1;
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return retval;
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}
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