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- // SPDX-License-Identifier: GPL-2.0-or-later
- /* mpih-rshift.c - MPI helper functions
- * Copyright (C) 1994, 1996, 1998, 1999,
- * 2000, 2001 Free Software Foundation, Inc.
- *
- * This file is part of GNUPG
- *
- * Note: This code is heavily based on the GNU MP Library.
- * Actually it's the same code with only minor changes in the
- * way the data is stored; this is to support the abstraction
- * of an optional secure memory allocation which may be used
- * to avoid revealing of sensitive data due to paging etc.
- * The GNU MP Library itself is published under the LGPL;
- * however I decided to publish this code under the plain GPL.
- */
- #include "mpi-internal.h"
- /* Shift U (pointed to by UP and USIZE limbs long) CNT bits to the right
- * and store the USIZE least significant limbs of the result at WP.
- * The bits shifted out to the right are returned.
- *
- * Argument constraints:
- * 1. 0 < CNT < BITS_PER_MP_LIMB
- * 2. If the result is to be written over the input, WP must be <= UP.
- */
- mpi_limb_t
- mpihelp_rshift(mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize, unsigned cnt)
- {
- mpi_limb_t high_limb, low_limb;
- unsigned sh_1, sh_2;
- mpi_size_t i;
- mpi_limb_t retval;
- sh_1 = cnt;
- wp -= 1;
- sh_2 = BITS_PER_MPI_LIMB - sh_1;
- high_limb = up[0];
- retval = high_limb << sh_2;
- low_limb = high_limb;
- for (i = 1; i < usize; i++) {
- high_limb = up[i];
- wp[i] = (low_limb >> sh_1) | (high_limb << sh_2);
- low_limb = high_limb;
- }
- wp[i] = low_limb >> sh_1;
- return retval;
- }
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