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 <linux/export.h>
15
16#include "mpi-internal.h"
17
18int mpi_add(MPI w, MPI u, MPI v)
19{
20 mpi_ptr_t wp, up, vp;
21 mpi_size_t usize, vsize, wsize;
22 int usign, vsign, wsign;
23 int err;
24
25 if (u->nlimbs < v->nlimbs) { /* Swap U and V. */
26 usize = v->nlimbs;
27 usign = v->sign;
28 vsize = u->nlimbs;
29 vsign = u->sign;
30 wsize = usize + 1;
31 err = RESIZE_IF_NEEDED(a: w, b: wsize);
32 if (err)
33 return err;
34 /* These must be after realloc (u or v may be the same as w). */
35 up = v->d;
36 vp = u->d;
37 } else {
38 usize = u->nlimbs;
39 usign = u->sign;
40 vsize = v->nlimbs;
41 vsign = v->sign;
42 wsize = usize + 1;
43 err = RESIZE_IF_NEEDED(a: w, b: wsize);
44 if (err)
45 return err;
46 /* These must be after realloc (u or v may be the same as w). */
47 up = u->d;
48 vp = v->d;
49 }
50 wp = w->d;
51 wsign = 0;
52
53 if (!vsize) { /* simple */
54 MPN_COPY(wp, up, usize);
55 wsize = usize;
56 wsign = usign;
57 } else if (usign != vsign) { /* different sign */
58 /* This test is right since USIZE >= VSIZE */
59 if (usize != vsize) {
60 mpihelp_sub(res_ptr: wp, s1_ptr: up, s1_size: usize, s2_ptr: vp, s2_size: vsize);
61 wsize = usize;
62 MPN_NORMALIZE(wp, wsize);
63 wsign = usign;
64 } else if (mpihelp_cmp(op1_ptr: up, op2_ptr: vp, size: usize) < 0) {
65 mpihelp_sub_n(res_ptr: wp, s1_ptr: vp, s2_ptr: up, size: usize);
66 wsize = usize;
67 MPN_NORMALIZE(wp, wsize);
68 if (!usign)
69 wsign = 1;
70 } else {
71 mpihelp_sub_n(res_ptr: wp, s1_ptr: up, s2_ptr: vp, size: usize);
72 wsize = usize;
73 MPN_NORMALIZE(wp, wsize);
74 if (usign)
75 wsign = 1;
76 }
77 } else { /* U and V have same sign. Add them. */
78 mpi_limb_t cy = mpihelp_add(res_ptr: wp, s1_ptr: up, s1_size: usize, s2_ptr: vp, s2_size: vsize);
79 wp[usize] = cy;
80 wsize = usize + cy;
81 if (usign)
82 wsign = 1;
83 }
84
85 w->nlimbs = wsize;
86 w->sign = wsign;
87 return 0;
88}
89EXPORT_SYMBOL_GPL(mpi_add);
90
91int mpi_sub(MPI w, MPI u, MPI v)
92{
93 int err;
94 MPI vv;
95
96 vv = mpi_copy(a: v);
97 if (!vv)
98 return -ENOMEM;
99
100 vv->sign = !vv->sign;
101 err = mpi_add(w, u, vv);
102 mpi_free(a: vv);
103
104 return err;
105}
106EXPORT_SYMBOL_GPL(mpi_sub);
107
108int mpi_addm(MPI w, MPI u, MPI v, MPI m)
109{
110 return mpi_add(w, u, v) ?:
111 mpi_mod(rem: w, dividend: w, divisor: m);
112}
113EXPORT_SYMBOL_GPL(mpi_addm);
114
115int mpi_subm(MPI w, MPI u, MPI v, MPI m)
116{
117 return mpi_sub(w, u, v) ?:
118 mpi_mod(rem: w, dividend: w, divisor: m);
119}
120EXPORT_SYMBOL_GPL(mpi_subm);
121

source code of linux/lib/crypto/mpi/mpi-add.c