1 /* mpi-add.c - MPI functions
2 * Copyright (C) 1994, 1996, 1998, 2001, 2002,
3 * 2003 Free Software Foundation, Inc.
4 *
5 * This file is part of Libgcrypt.
6 *
7 * Note: This code is heavily based on the GNU MP Library.
8 * Actually it's the same code with only minor changes in the
9 * way the data is stored; this is to support the abstraction
10 * of an optional secure memory allocation which may be used
11 * to avoid revealing of sensitive data due to paging etc.
12 */
13
14 #include "mpi-internal.h"
15
16 /****************
17 * Add the unsigned integer V to the mpi-integer U and store the
18 * result in W. U and V may be the same.
19 */
20 void mpi_add_ui(MPI w, MPI u, unsigned long v)
21 {
22 mpi_ptr_t wp, up;
23 mpi_size_t usize, wsize;
24 int usign, wsign;
25
26 usize = u->nlimbs;
27 usign = u->sign;
28 wsign = 0;
29
30 /* If not space for W (and possible carry), increase space. */
31 wsize = usize + 1;
32 if (w->alloced < wsize)
33 mpi_resize(w, wsize);
34
35 /* These must be after realloc (U may be the same as W). */
36 up = u->d;
37 wp = w->d;
38
39 if (!usize) { /* simple */
40 wp[0] = v;
41 wsize = v ? 1:0;
42 } else if (!usign) { /* mpi is not negative */
43 mpi_limb_t cy;
44 cy = mpihelp_add_1(wp, up, usize, v);
45 wp[usize] = cy;
46 wsize = usize + cy;
47 } else {
48 /* The signs are different. Need exact comparison to determine
49 * which operand to subtract from which.
50 */
51 if (usize == 1 && up[0] < v) {
52 wp[0] = v - up[0];
53 wsize = 1;
54 } else {
55 mpihelp_sub_1(wp, up, usize, v);
56 /* Size can decrease with at most one limb. */
57 wsize = usize - (wp[usize-1] == 0);
58 wsign = 1;
59 }
60 }
61
62 w->nlimbs = wsize;
63 w->sign = wsign;
64 }
65
66
67 void mpi_add(MPI w, MPI u, MPI v)
68 {
69 mpi_ptr_t wp, up, vp;
70 mpi_size_t usize, vsize, wsize;
71 int usign, vsign, wsign;
72
73 if (u->nlimbs < v->nlimbs) { /* Swap U and V. */
74 usize = v->nlimbs;
75 usign = v->sign;
76 vsize = u->nlimbs;
77 vsign = u->sign;
78 wsize = usize + 1;
79 RESIZE_IF_NEEDED(w, wsize);
80 /* These must be after realloc (u or v may be the same as w). */
81 up = v->d;
82 vp = u->d;
83 } else {
84 usize = u->nlimbs;
85 usign = u->sign;
86 vsize = v->nlimbs;
87 vsign = v->sign;
88 wsize = usize + 1;
89 RESIZE_IF_NEEDED(w, wsize);
90 /* These must be after realloc (u or v may be the same as w). */
91 up = u->d;
92 vp = v->d;
93 }
94 wp = w->d;
95 wsign = 0;
96
97 if (!vsize) { /* simple */
98 MPN_COPY(wp, up, usize);
99 wsize = usize;
100 wsign = usign;
101 } else if (usign != vsign) { /* different sign */
102 /* This test is right since USIZE >= VSIZE */
103 if (usize != vsize) {
104 mpihelp_sub(wp, up, usize, vp, vsize);
105 wsize = usize;
106 MPN_NORMALIZE(wp, wsize);
107 wsign = usign;
108 } else if (mpihelp_cmp(up, vp, usize) < 0) {
109 mpihelp_sub_n(wp, vp, up, usize);
110 wsize = usize;
111 MPN_NORMALIZE(wp, wsize);
112 if (!usign)
113 wsign = 1;
114 } else {
115 mpihelp_sub_n(wp, up, vp, usize);
116 wsize = usize;
117 MPN_NORMALIZE(wp, wsize);
118 if (usign)
119 wsign = 1;
120 }
121 } else { /* U and V have same sign. Add them. */
122 mpi_limb_t cy = mpihelp_add(wp, up, usize, vp, vsize);
123 wp[usize] = cy;
124 wsize = usize + cy;
125 if (usign)
126 wsign = 1;
127 }
128
129 w->nlimbs = wsize;
130 w->sign = wsign;
131 }
132 EXPORT_SYMBOL_GPL(mpi_add);
133
134 void mpi_sub(MPI w, MPI u, MPI v)
135 {
136 MPI vv = mpi_copy(v);
137 vv->sign = !vv->sign;
138 mpi_add(w, u, vv);
139 mpi_free(vv);
140 }
141 EXPORT_SYMBOL_GPL(mpi_sub);
142
143 void mpi_addm(MPI w, MPI u, MPI v, MPI m)
144 {
145 mpi_add(w, u, v);
146 mpi_mod(w, w, m);
147 }
148 EXPORT_SYMBOL_GPL(mpi_addm);
149
150 void mpi_subm(MPI w, MPI u, MPI v, MPI m)
151 {
152 mpi_sub(w, u, v);
153 mpi_mod(w, w, m);
154 }
155 EXPORT_SYMBOL_GPL(mpi_subm);
156
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