aboutsummaryrefslogtreecommitdiffstats
path: root/lib/mpi/mpi-add.c
blob: f56b9ba295e68766b390a6c9458897498b43084b (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
/* mpi-add.c  -  MPI functions
 *	Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
 *	Copyright (C) 1994, 1996 Free Software Foundation, Inc.
 *
 * This file is part of GnuPG.
 *
 * GnuPG is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * GnuPG is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
 *
 * Note: This code is heavily based on the GNU MP Library.
 *	 Actually it's the same code with only minor changes in the
 *	 way the data is stored; this is to support the abstraction
 *	 of an optional secure memory allocation which may be used
 *	 to avoid revealing of sensitive data due to paging etc.
 *	 The GNU MP Library itself is published under the LGPL;
 *	 however I decided to publish this code under the plain GPL.
 */

#include "mpi-internal.h"

/****************
 * Add the unsigned integer V to the mpi-integer U and store the
 * result in W. U and V may be the same.
 */
int mpi_add_ui(MPI w, const MPI u, unsigned long v)
{
	mpi_ptr_t wp, up;
	mpi_size_t usize, wsize;
	int usign, wsign;

	usize = u->nlimbs;
	usign = u->sign;
	wsign = 0;

	/* If not space for W (and possible carry), increase space.  */
	wsize = usize + 1;
	if (w->alloced < wsize)
		if (mpi_resize(w, wsize) < 0)
			return -ENOMEM;

	/* These must be after realloc (U may be the same as W).  */
	up = u->d;
	wp = w->d;

	if (!usize) {		/* simple */
		wp[0] = v;
		wsize = v ? 1 : 0;
	} else if (!usign) {	/* mpi is not negative */
		mpi_limb_t cy;
		cy = mpihelp_add_1(wp, up, usize, v);
		wp[usize] = cy;
		wsize = usize + cy;
	} else {		/* The signs are different.  Need exact comparison to determine
				 * which operand to subtract from which.  */
		if (usize == 1 && up[0] < v) {
			wp[0] = v - up[0];
			wsize = 1;
		} else {
			mpihelp_sub_1(wp, up, usize, v);
			/* Size can decrease with at most one limb. */
			wsize = usize - (wp[usize - 1] == 0);
			wsign = 1;
		}
	}

	w->nlimbs = wsize;
	w->sign = wsign;
	return 0;
}

int mpi_add(MPI w, MPI u, MPI v)
{
	mpi_ptr_t wp, up, vp;
	mpi_size_t usize, vsize, wsize;
	int usign, vsign, wsign;

	if (u->nlimbs < v->nlimbs) {	/* Swap U and V. */
		usize = v->nlimbs;
		usign = v->sign;
		vsize = u->nlimbs;
		vsign = u->sign;
		wsize = usize + 1;
		if (RESIZE_IF_NEEDED(w, wsize) < 0)
			return -ENOMEM;
		/* These must be after realloc (u or v may be the same as w).  */
		up = v->d;
		vp = u->d;
	} else {
		usize = u->nlimbs;
		usign = u->sign;
		vsize = v->nlimbs;
		vsign = v->sign;
		wsize = usize + 1;
		if (RESIZE_IF_NEEDED(w, wsize) < 0)
			return -ENOMEM;
		/* These must be after realloc (u or v may be the same as w).  */
		up = u->d;
		vp = v->d;
	}
	wp = w->d;
	wsign = 0;

	if (!vsize) {		/* simple */
		MPN_COPY(wp, up, usize);
		wsize = usize;
		wsign = usign;
	} else if (usign != vsign) {	/* different sign */
		/* This test is right since USIZE >= VSIZE */
		if (usize != vsize) {
			mpihelp_sub(wp, up, usize, vp, vsize);
			wsize = usize;
			MPN_NORMALIZE(wp, wsize);
			wsign = usign;
		} else if (mpihelp_cmp(up, vp, usize) < 0) {
			mpihelp_sub_n(wp, vp, up, usize);
			wsize = usize;
			MPN_NORMALIZE(wp, wsize);
			if (!usign)
				wsign = 1;
		} else {
			mpihelp_sub_n(wp, up, vp, usize);
			wsize = usize;
			MPN_NORMALIZE(wp, wsize);
			if (usign)
				wsign = 1;
		}
	} else {		/* U and V have same sign. Add them. */
		mpi_limb_t cy = mpihelp_add(wp, up, usize, vp, vsize);
		wp[usize] = cy;
		wsize = usize + cy;
		if (usign)
			wsign = 1;
	}

	w->nlimbs = wsize;
	w->sign = wsign;
	return 0;
}

/****************
 * Subtract the unsigned integer V from the mpi-integer U and store the
 * result in W.
 */
int mpi_sub_ui(MPI w, MPI u, unsigned long v)
{
	mpi_ptr_t wp, up;
	mpi_size_t usize, wsize;
	int usign, wsign;

	usize = u->nlimbs;
	usign = u->sign;
	wsign = 0;

	/* If not space for W (and possible carry), increase space.  */
	wsize = usize + 1;
	if (w->alloced < wsize)
		if (mpi_resize(w, wsize) < 0)
			return -ENOMEM;

	/* These must be after realloc (U may be the same as W).  */
	up = u->d;
	wp = w->d;

	if (!usize) {		/* simple */
		wp[0] = v;
		wsize = v ? 1 : 0;
		wsign = 1;
	} else if (usign) {	/* mpi and v are negative */
		mpi_limb_t cy;
		cy = mpihelp_add_1(wp, up, usize, v);
		wp[usize] = cy;
		wsize = usize + cy;
	} else {		/* The signs are different.  Need exact comparison to determine
				 * which operand to subtract from which.  */
		if (usize == 1 && up[0] < v) {
			wp[0] = v - up[0];
			wsize = 1;
			wsign = 1;
		} else {
			mpihelp_sub_1(wp, up, usize, v);
			/* Size can decrease with at most one limb. */
			wsize = usize - (wp[usize - 1] == 0);
		}
	}

	w->nlimbs = wsize;
	w->sign = wsign;
	return 0;
}

int mpi_sub(MPI w, MPI u, MPI v)
{
	int rc;

	if (w == v) {
		MPI vv;
		if (mpi_copy(&vv, v) < 0)
			return -ENOMEM;
		vv->sign = !vv->sign;
		rc = mpi_add(w, u, vv);
		mpi_free(vv);
	} else {
		/* fixme: this is not thread-save (we temp. modify v) */
		v->sign = !v->sign;
		rc = mpi_add(w, u, v);
		v->sign = !v->sign;
	}
	return rc;
}

int mpi_addm(MPI w, MPI u, MPI v, MPI m)
{
	if (mpi_add(w, u, v) < 0 || mpi_fdiv_r(w, w, m) < 0)
		return -ENOMEM;
	return 0;
}

int mpi_subm(MPI w, MPI u, MPI v, MPI m)
{
	if (mpi_sub(w, u, v) < 0 || mpi_fdiv_r(w, w, m) < 0)
		return -ENOMEM;
	return 0;
}