1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* mpihelp-lshift.c - MPI helper functions 3 * 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 the 9 * way the data is stored; this is to support the abstraction 10 * of an optional secure memory allocation which may be used 11 * 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 left 19 * 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_LIMB 24 * 2. If the result is to be written over the input, WP must be >= UP. 25 */ 26 27 mpi_limb_t 28 mpihelp_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