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1// SPDX-License-Identifier: GPL-2.0-or-later2/* mpihelp-lshift.c - MPI helper functions3 * Copyright (C) 1994, 1996, 1998, 2001 Free Software Foundation, Inc.4 *5 * This file is part of GnuPG.6 *7 * Note: This code is heavily based on the GNU MP Library.8 * Actually it's the same code with only minor changes in the9 * way the data is stored; this is to support the abstraction10 * of an optional secure memory allocation which may be used11 * to avoid revealing of sensitive data due to paging etc.12 * The GNU MP Library itself is published under the LGPL;13 * however I decided to publish this code under the plain GPL.14 */15 16#include "mpi-internal.h"17 18/* Shift U (pointed to by UP and USIZE digits long) CNT bits to the left19 * and store the USIZE least significant digits of the result at WP.20 * Return the bits shifted out from the most significant digit.21 *22 * Argument constraints:23 * 1. 0 < CNT < BITS_PER_MP_LIMB24 * 2. If the result is to be written over the input, WP must be >= UP.25 */26 27mpi_limb_t28mpihelp_lshift(mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize, unsigned int cnt)29{30 mpi_limb_t high_limb, low_limb;31 unsigned sh_1, sh_2;32 mpi_size_t i;33 mpi_limb_t retval;34 35 sh_1 = cnt;36 wp += 1;37 sh_2 = BITS_PER_MPI_LIMB - sh_1;38 i = usize - 1;39 low_limb = up[i];40 retval = low_limb >> sh_2;41 high_limb = low_limb;42 while (--i >= 0) {43 low_limb = up[i];44 wp[i] = (high_limb << sh_1) | (low_limb >> sh_2);45 high_limb = low_limb;46 }47 wp[i] = high_limb << sh_1;48 49 return retval;50}51