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 */
20void 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
67void 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}
132EXPORT_SYMBOL_GPL(mpi_add);
133
134void 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}
141EXPORT_SYMBOL_GPL(mpi_sub);
142
143void mpi_addm(MPI w, MPI u, MPI v, MPI m)
144{
145	mpi_add(w, u, v);
146	mpi_mod(w, w, m);
147}
148EXPORT_SYMBOL_GPL(mpi_addm);
149
150void mpi_subm(MPI w, MPI u, MPI v, MPI m)
151{
152	mpi_sub(w, u, v);
153	mpi_mod(w, w, m);
154}
155EXPORT_SYMBOL_GPL(mpi_subm);
156