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1/* mpi-add.c - MPI functions
2 * Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
3 * Copyright (C) 1994, 1996 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
32/****************
33 * Add the unsigned integer V to the mpi-integer U and store the
34 * result in W. U and V may be the same.
35 */
36int mpi_add_ui(MPI w, const MPI u, unsigned long v)
37{
38 mpi_ptr_t wp, up;
39 mpi_size_t usize, wsize;
40 int usign, wsign;
41
42 usize = u->nlimbs;
43 usign = u->sign;
44 wsign = 0;
45
46 /* If not space for W (and possible carry), increase space. */
47 wsize = usize + 1;
48 if (w->alloced < wsize)
49 if (mpi_resize(w, wsize) < 0)
50 return -ENOMEM;
51
52 /* These must be after realloc (U may be the same as W). */
53 up = u->d;
54 wp = w->d;
55
56 if (!usize) { /* simple */
57 wp[0] = v;
58 wsize = v ? 1 : 0;
59 } else if (!usign) { /* mpi is not negative */
60 mpi_limb_t cy;
61 cy = mpihelp_add_1(wp, up, usize, v);
62 wp[usize] = cy;
63 wsize = usize + cy;
64 } else { /* The signs are different. Need exact comparison to determine
65 * which operand to subtract from which. */
66 if (usize == 1 && up[0] < v) {
67 wp[0] = v - up[0];
68 wsize = 1;
69 } else {
70 mpihelp_sub_1(wp, up, usize, v);
71 /* Size can decrease with at most one limb. */
72 wsize = usize - (wp[usize - 1] == 0);
73 wsign = 1;
74 }
75 }
76
77 w->nlimbs = wsize;
78 w->sign = wsign;
79 return 0;
80}
81
82int mpi_add(MPI w, MPI u, MPI v)
83{
84 mpi_ptr_t wp, up, vp;
85 mpi_size_t usize, vsize, wsize;
86 int usign, vsign, wsign;
87
88 if (u->nlimbs < v->nlimbs) { /* Swap U and V. */
89 usize = v->nlimbs;
90 usign = v->sign;
91 vsize = u->nlimbs;
92 vsign = u->sign;
93 wsize = usize + 1;
94 if (RESIZE_IF_NEEDED(w, wsize) < 0)
95 return -ENOMEM;
96 /* These must be after realloc (u or v may be the same as w). */
97 up = v->d;
98 vp = u->d;
99 } else {
100 usize = u->nlimbs;
101 usign = u->sign;
102 vsize = v->nlimbs;
103 vsign = v->sign;
104 wsize = usize + 1;
105 if (RESIZE_IF_NEEDED(w, wsize) < 0)
106 return -ENOMEM;
107 /* These must be after realloc (u or v may be the same as w). */
108 up = u->d;
109 vp = v->d;
110 }
111 wp = w->d;
112 wsign = 0;
113
114 if (!vsize) { /* simple */
115 MPN_COPY(wp, up, usize);
116 wsize = usize;
117 wsign = usign;
118 } else if (usign != vsign) { /* different sign */
119 /* This test is right since USIZE >= VSIZE */
120 if (usize != vsize) {
121 mpihelp_sub(wp, up, usize, vp, vsize);
122 wsize = usize;
123 MPN_NORMALIZE(wp, wsize);
124 wsign = usign;
125 } else if (mpihelp_cmp(up, vp, usize) < 0) {
126 mpihelp_sub_n(wp, vp, up, usize);
127 wsize = usize;
128 MPN_NORMALIZE(wp, wsize);
129 if (!usign)
130 wsign = 1;
131 } else {
132 mpihelp_sub_n(wp, up, vp, usize);
133 wsize = usize;
134 MPN_NORMALIZE(wp, wsize);
135 if (usign)
136 wsign = 1;
137 }
138 } else { /* U and V have same sign. Add them. */
139 mpi_limb_t cy = mpihelp_add(wp, up, usize, vp, vsize);
140 wp[usize] = cy;
141 wsize = usize + cy;
142 if (usign)
143 wsign = 1;
144 }
145
146 w->nlimbs = wsize;
147 w->sign = wsign;
148 return 0;
149}
150
151/****************
152 * Subtract the unsigned integer V from the mpi-integer U and store the
153 * result in W.
154 */
155int mpi_sub_ui(MPI w, MPI u, unsigned long v)
156{
157 mpi_ptr_t wp, up;
158 mpi_size_t usize, wsize;
159 int usign, wsign;
160
161 usize = u->nlimbs;
162 usign = u->sign;
163 wsign = 0;
164
165 /* If not space for W (and possible carry), increase space. */
166 wsize = usize + 1;
167 if (w->alloced < wsize)
168 if (mpi_resize(w, wsize) < 0)
169 return -ENOMEM;
170
171 /* These must be after realloc (U may be the same as W). */
172 up = u->d;
173 wp = w->d;
174
175 if (!usize) { /* simple */
176 wp[0] = v;
177 wsize = v ? 1 : 0;
178 wsign = 1;
179 } else if (usign) { /* mpi and v are negative */
180 mpi_limb_t cy;
181 cy = mpihelp_add_1(wp, up, usize, v);
182 wp[usize] = cy;
183 wsize = usize + cy;
184 } else { /* The signs are different. Need exact comparison to determine
185 * which operand to subtract from which. */
186 if (usize == 1 && up[0] < v) {
187 wp[0] = v - up[0];
188 wsize = 1;
189 wsign = 1;
190 } else {
191 mpihelp_sub_1(wp, up, usize, v);
192 /* Size can decrease with at most one limb. */
193 wsize = usize - (wp[usize - 1] == 0);
194 }
195 }
196
197 w->nlimbs = wsize;
198 w->sign = wsign;
199 return 0;
200}
201
202int mpi_sub(MPI w, MPI u, MPI v)
203{
204 int rc;
205
206 if (w == v) {
207 MPI vv;
208 if (mpi_copy(&vv, v) < 0)
209 return -ENOMEM;
210 vv->sign = !vv->sign;
211 rc = mpi_add(w, u, vv);
212 mpi_free(vv);
213 } else {
214 /* fixme: this is not thread-save (we temp. modify v) */
215 v->sign = !v->sign;
216 rc = mpi_add(w, u, v);
217 v->sign = !v->sign;
218 }
219 return rc;
220}
221
222int mpi_addm(MPI w, MPI u, MPI v, MPI m)
223{
224 if (mpi_add(w, u, v) < 0 || mpi_fdiv_r(w, w, m) < 0)
225 return -ENOMEM;
226 return 0;
227}
228
229int mpi_subm(MPI w, MPI u, MPI v, MPI m)
230{
231 if (mpi_sub(w, u, v) < 0 || mpi_fdiv_r(w, w, m) < 0)
232 return -ENOMEM;
233 return 0;
234}