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generic_mpih-add1.c
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1 /* mpihelp-add_1.c - MPI helper functions
2  * Copyright (C) 1994, 1996, 1997, 1998,
3  * 2000 Free Software Foundation, Inc.
4  *
5  * This file is part of GnuPG.
6  *
7  * GnuPG is free software; you can redistribute it and/or modify
8  * it under the terms of the GNU General Public License as published by
9  * the Free Software Foundation; either version 2 of the License, or
10  * (at your option) any later version.
11  *
12  * GnuPG is distributed in the hope that it will be useful,
13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15  * GNU General Public License for more details.
16  *
17  * You should have received a copy of the GNU General Public License
18  * along with this program; if not, write to the Free Software
19  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
20  *
21  * Note: This code is heavily based on the GNU MP Library.
22  * Actually it's the same code with only minor changes in the
23  * way the data is stored; this is to support the abstraction
24  * of an optional secure memory allocation which may be used
25  * to avoid revealing of sensitive data due to paging etc.
26  * The GNU MP Library itself is published under the LGPL;
27  * however I decided to publish this code under the plain GPL.
28  */
29 
30 #include "mpi-internal.h"
31 #include "longlong.h"
32 
35  mpi_ptr_t s2_ptr, mpi_size_t size)
36 {
37  mpi_limb_t x, y, cy;
38  mpi_size_t j;
39 
40  /* The loop counter and index J goes from -SIZE to -1. This way
41  the loop becomes faster. */
42  j = -size;
43 
44  /* Offset the base pointers to compensate for the negative indices. */
45  s1_ptr -= j;
46  s2_ptr -= j;
47  res_ptr -= j;
48 
49  cy = 0;
50  do {
51  y = s2_ptr[j];
52  x = s1_ptr[j];
53  y += cy; /* add previous carry to one addend */
54  cy = y < cy; /* get out carry from that addition */
55  y += x; /* add other addend */
56  cy += y < x; /* get out carry from that add, combine */
57  res_ptr[j] = y;
58  } while (++j);
59 
60  return cy;
61 }