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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 : 0 : mpihelp_lshift(mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize, unsigned int cnt) 29 : : { 30 : 0 : mpi_limb_t high_limb, low_limb; 31 : 0 : unsigned sh_1, sh_2; 32 : 0 : mpi_size_t i; 33 : 0 : mpi_limb_t retval; 34 : : 35 : 0 : sh_1 = cnt; 36 : 0 : wp += 1; 37 : 0 : sh_2 = BITS_PER_MPI_LIMB - sh_1; 38 : 0 : i = usize - 1; 39 : 0 : low_limb = up[i]; 40 : 0 : retval = low_limb >> sh_2; 41 : 0 : high_limb = low_limb; 42 [ # # ]: 0 : while (--i >= 0) { 43 : 0 : low_limb = up[i]; 44 : 0 : wp[i] = (high_limb << sh_1) | (low_limb >> sh_2); 45 : 0 : high_limb = low_limb; 46 : : } 47 : 0 : wp[i] = high_limb << sh_1; 48 : : 49 : 0 : return retval; 50 : : }