// 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; }