^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 1) // SPDX-License-Identifier: GPL-2.0-or-later
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 2) /* mpihelp-lshift.c - MPI helper functions
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 3) * Copyright (C) 1994, 1996, 1998, 2001 Free Software Foundation, Inc.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 4) *
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 5) * This file is part of GnuPG.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 6) *
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 7) * Note: This code is heavily based on the GNU MP Library.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 8) * Actually it's the same code with only minor changes in the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 9) * way the data is stored; this is to support the abstraction
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 10) * of an optional secure memory allocation which may be used
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 11) * to avoid revealing of sensitive data due to paging etc.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 12) * The GNU MP Library itself is published under the LGPL;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 13) * however I decided to publish this code under the plain GPL.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 14) */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 15)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 16) #include "mpi-internal.h"
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 17)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 18) /* Shift U (pointed to by UP and USIZE digits long) CNT bits to the left
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 19) * and store the USIZE least significant digits of the result at WP.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 20) * Return the bits shifted out from the most significant digit.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 21) *
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 22) * Argument constraints:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 23) * 1. 0 < CNT < BITS_PER_MP_LIMB
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 24) * 2. If the result is to be written over the input, WP must be >= UP.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 25) */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 26)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 27) mpi_limb_t
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 28) mpihelp_lshift(mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize, unsigned int cnt)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 29) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 30) mpi_limb_t high_limb, low_limb;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 31) unsigned sh_1, sh_2;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 32) mpi_size_t i;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 33) mpi_limb_t retval;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 34)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 35) sh_1 = cnt;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 36) wp += 1;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 37) sh_2 = BITS_PER_MPI_LIMB - sh_1;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 38) i = usize - 1;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 39) low_limb = up[i];
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 40) retval = low_limb >> sh_2;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 41) high_limb = low_limb;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 42) while (--i >= 0) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 43) low_limb = up[i];
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 44) wp[i] = (high_limb << sh_1) | (low_limb >> sh_2);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 45) high_limb = low_limb;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 46) }
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 47) wp[i] = high_limb << sh_1;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 48)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 49) return retval;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 50) }