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