1*4882a593Smuzhiyun // SPDX-License-Identifier: GPL-2.0-or-later
2*4882a593Smuzhiyun /* mpihelp-add_1.c - MPI helper functions
3*4882a593Smuzhiyun * Copyright (C) 1994, 1996, 1997, 1998,
4*4882a593Smuzhiyun * 2000 Free Software Foundation, Inc.
5*4882a593Smuzhiyun *
6*4882a593Smuzhiyun * This file is part of GnuPG.
7*4882a593Smuzhiyun *
8*4882a593Smuzhiyun * Note: This code is heavily based on the GNU MP Library.
9*4882a593Smuzhiyun * Actually it's the same code with only minor changes in the
10*4882a593Smuzhiyun * way the data is stored; this is to support the abstraction
11*4882a593Smuzhiyun * of an optional secure memory allocation which may be used
12*4882a593Smuzhiyun * to avoid revealing of sensitive data due to paging etc.
13*4882a593Smuzhiyun * The GNU MP Library itself is published under the LGPL;
14*4882a593Smuzhiyun * however I decided to publish this code under the plain GPL.
15*4882a593Smuzhiyun */
16*4882a593Smuzhiyun
17*4882a593Smuzhiyun #include "mpi-internal.h"
18*4882a593Smuzhiyun #include "longlong.h"
19*4882a593Smuzhiyun
20*4882a593Smuzhiyun mpi_limb_t
mpihelp_add_n(mpi_ptr_t res_ptr,mpi_ptr_t s1_ptr,mpi_ptr_t s2_ptr,mpi_size_t size)21*4882a593Smuzhiyun mpihelp_add_n(mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
22*4882a593Smuzhiyun mpi_ptr_t s2_ptr, mpi_size_t size)
23*4882a593Smuzhiyun {
24*4882a593Smuzhiyun mpi_limb_t x, y, cy;
25*4882a593Smuzhiyun mpi_size_t j;
26*4882a593Smuzhiyun
27*4882a593Smuzhiyun /* The loop counter and index J goes from -SIZE to -1. This way
28*4882a593Smuzhiyun the loop becomes faster. */
29*4882a593Smuzhiyun j = -size;
30*4882a593Smuzhiyun
31*4882a593Smuzhiyun /* Offset the base pointers to compensate for the negative indices. */
32*4882a593Smuzhiyun s1_ptr -= j;
33*4882a593Smuzhiyun s2_ptr -= j;
34*4882a593Smuzhiyun res_ptr -= j;
35*4882a593Smuzhiyun
36*4882a593Smuzhiyun cy = 0;
37*4882a593Smuzhiyun do {
38*4882a593Smuzhiyun y = s2_ptr[j];
39*4882a593Smuzhiyun x = s1_ptr[j];
40*4882a593Smuzhiyun y += cy; /* add previous carry to one addend */
41*4882a593Smuzhiyun cy = y < cy; /* get out carry from that addition */
42*4882a593Smuzhiyun y += x; /* add other addend */
43*4882a593Smuzhiyun cy += y < x; /* get out carry from that add, combine */
44*4882a593Smuzhiyun res_ptr[j] = y;
45*4882a593Smuzhiyun } while (++j);
46*4882a593Smuzhiyun
47*4882a593Smuzhiyun return cy;
48*4882a593Smuzhiyun }
49