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  */
mpi_add_ui(MPI w,MPI u,unsigned long v)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 
mpi_add(MPI w,MPI u,MPI v)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 
mpi_sub(MPI w,MPI u,MPI v)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 
142 
mpi_addm(MPI w,MPI u,MPI v,MPI m)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 
mpi_subm(MPI w,MPI u,MPI v,MPI m)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