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465ae836 | 1 | // SPDX-License-Identifier: GPL-2.0-or-later |
cdec9cb5 DK |
2 | /* mpihelp-add_1.c - MPI helper functions |
3 | * Copyright (C) 1994, 1996, 1997, 1998, | |
4 | * 2000 Free Software Foundation, Inc. | |
5 | * | |
6 | * This file is part of GnuPG. | |
7 | * | |
cdec9cb5 DK |
8 | * Note: This code is heavily based on the GNU MP Library. |
9 | * Actually it's the same code with only minor changes in the | |
10 | * way the data is stored; this is to support the abstraction | |
11 | * of an optional secure memory allocation which may be used | |
12 | * to avoid revealing of sensitive data due to paging etc. | |
13 | * The GNU MP Library itself is published under the LGPL; | |
14 | * however I decided to publish this code under the plain GPL. | |
15 | */ | |
16 | ||
17 | #include "mpi-internal.h" | |
18 | #include "longlong.h" | |
19 | ||
20 | mpi_limb_t | |
21 | mpihelp_add_n(mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr, | |
22 | mpi_ptr_t s2_ptr, mpi_size_t size) | |
23 | { | |
24 | mpi_limb_t x, y, cy; | |
25 | mpi_size_t j; | |
26 | ||
27 | /* The loop counter and index J goes from -SIZE to -1. This way | |
28 | the loop becomes faster. */ | |
29 | j = -size; | |
30 | ||
31 | /* Offset the base pointers to compensate for the negative indices. */ | |
32 | s1_ptr -= j; | |
33 | s2_ptr -= j; | |
34 | res_ptr -= j; | |
35 | ||
36 | cy = 0; | |
37 | do { | |
38 | y = s2_ptr[j]; | |
39 | x = s1_ptr[j]; | |
40 | y += cy; /* add previous carry to one addend */ | |
41 | cy = y < cy; /* get out carry from that addition */ | |
42 | y += x; /* add other addend */ | |
43 | cy += y < x; /* get out carry from that add, combine */ | |
44 | res_ptr[j] = y; | |
45 | } while (++j); | |
46 | ||
47 | return cy; | |
48 | } |