1*4882a593Smuzhiyun // SPDX-License-Identifier: GPL-2.0-or-later
2*4882a593Smuzhiyun /* mpihelp-lshift.c - MPI helper functions
3*4882a593Smuzhiyun * Copyright (C) 1994, 1996, 1998, 2001 Free Software Foundation, Inc.
4*4882a593Smuzhiyun *
5*4882a593Smuzhiyun * This file is part of GnuPG.
6*4882a593Smuzhiyun *
7*4882a593Smuzhiyun * Note: This code is heavily based on the GNU MP Library.
8*4882a593Smuzhiyun * Actually it's the same code with only minor changes in the
9*4882a593Smuzhiyun * way the data is stored; this is to support the abstraction
10*4882a593Smuzhiyun * of an optional secure memory allocation which may be used
11*4882a593Smuzhiyun * to avoid revealing of sensitive data due to paging etc.
12*4882a593Smuzhiyun * The GNU MP Library itself is published under the LGPL;
13*4882a593Smuzhiyun * however I decided to publish this code under the plain GPL.
14*4882a593Smuzhiyun */
15*4882a593Smuzhiyun
16*4882a593Smuzhiyun #include "mpi-internal.h"
17*4882a593Smuzhiyun
18*4882a593Smuzhiyun /* Shift U (pointed to by UP and USIZE digits long) CNT bits to the left
19*4882a593Smuzhiyun * and store the USIZE least significant digits of the result at WP.
20*4882a593Smuzhiyun * Return the bits shifted out from the most significant digit.
21*4882a593Smuzhiyun *
22*4882a593Smuzhiyun * Argument constraints:
23*4882a593Smuzhiyun * 1. 0 < CNT < BITS_PER_MP_LIMB
24*4882a593Smuzhiyun * 2. If the result is to be written over the input, WP must be >= UP.
25*4882a593Smuzhiyun */
26*4882a593Smuzhiyun
27*4882a593Smuzhiyun mpi_limb_t
mpihelp_lshift(mpi_ptr_t wp,mpi_ptr_t up,mpi_size_t usize,unsigned int cnt)28*4882a593Smuzhiyun mpihelp_lshift(mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize, unsigned int cnt)
29*4882a593Smuzhiyun {
30*4882a593Smuzhiyun mpi_limb_t high_limb, low_limb;
31*4882a593Smuzhiyun unsigned sh_1, sh_2;
32*4882a593Smuzhiyun mpi_size_t i;
33*4882a593Smuzhiyun mpi_limb_t retval;
34*4882a593Smuzhiyun
35*4882a593Smuzhiyun sh_1 = cnt;
36*4882a593Smuzhiyun wp += 1;
37*4882a593Smuzhiyun sh_2 = BITS_PER_MPI_LIMB - sh_1;
38*4882a593Smuzhiyun i = usize - 1;
39*4882a593Smuzhiyun low_limb = up[i];
40*4882a593Smuzhiyun retval = low_limb >> sh_2;
41*4882a593Smuzhiyun high_limb = low_limb;
42*4882a593Smuzhiyun while (--i >= 0) {
43*4882a593Smuzhiyun low_limb = up[i];
44*4882a593Smuzhiyun wp[i] = (high_limb << sh_1) | (low_limb >> sh_2);
45*4882a593Smuzhiyun high_limb = low_limb;
46*4882a593Smuzhiyun }
47*4882a593Smuzhiyun wp[i] = high_limb << sh_1;
48*4882a593Smuzhiyun
49*4882a593Smuzhiyun return retval;
50*4882a593Smuzhiyun }
51