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1/* mpicoder.c - Coder for the external representation of MPIs
2 * Copyright (C) 1998, 1999 Free Software Foundation, Inc.
3 *
4 * This file is part of GnuPG.
5 *
6 * GnuPG is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or
9 * (at your option) any later version.
10 *
11 * GnuPG is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
15 *
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, write to the Free Software
18 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
19 */
20
21#include "mpi-internal.h"
22
23#define MAX_EXTERN_MPI_BITS 16384
24
25MPI mpi_read_from_buffer(const void *xbuffer, unsigned *ret_nread)
26{
27 const uint8_t *buffer = xbuffer;
28 int i, j;
29 unsigned nbits, nbytes, nlimbs, nread = 0;
30 mpi_limb_t a;
31 MPI val = NULL;
32
33 if (*ret_nread < 2)
34 goto leave;
35 nbits = buffer[0] << 8 | buffer[1];
36
37 if (nbits > MAX_EXTERN_MPI_BITS) {
38 pr_info("MPI: mpi too large (%u bits)\n", nbits);
39 goto leave;
40 }
41 buffer += 2;
42 nread = 2;
43
44 nbytes = (nbits + 7) / 8;
45 nlimbs = (nbytes + BYTES_PER_MPI_LIMB - 1) / BYTES_PER_MPI_LIMB;
46 val = mpi_alloc(nlimbs);
47 if (!val)
48 return NULL;
49 i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
50 i %= BYTES_PER_MPI_LIMB;
51 val->nbits = nbits;
52 j = val->nlimbs = nlimbs;
53 val->sign = 0;
54 for (; j > 0; j--) {
55 a = 0;
56 for (; i < BYTES_PER_MPI_LIMB; i++) {
57 if (++nread > *ret_nread) {
58 printk
59 ("MPI: mpi larger than buffer nread=%d ret_nread=%d\n",
60 nread, *ret_nread);
61 goto leave;
62 }
63 a <<= 8;
64 a |= *buffer++;
65 }
66 i = 0;
67 val->d[j - 1] = a;
68 }
69
70leave:
71 *ret_nread = nread;
72 return val;
73}
74EXPORT_SYMBOL_GPL(mpi_read_from_buffer);
75
76/****************
77 * Return an allocated buffer with the MPI (msb first).
78 * NBYTES receives the length of this buffer. Caller must free the
79 * return string (This function does return a 0 byte buffer with NBYTES
80 * set to zero if the value of A is zero. If sign is not NULL, it will
81 * be set to the sign of the A.
82 */
83void *mpi_get_buffer(MPI a, unsigned *nbytes, int *sign)
84{
85 uint8_t *p, *buffer;
86 mpi_limb_t alimb;
87 int i;
88 unsigned int n;
89
90 if (sign)
91 *sign = a->sign;
92 *nbytes = n = a->nlimbs * BYTES_PER_MPI_LIMB;
93 if (!n)
94 n++; /* avoid zero length allocation */
95 p = buffer = kmalloc(n, GFP_KERNEL);
96 if (!p)
97 return NULL;
98
99 for (i = a->nlimbs - 1; i >= 0; i--) {
100 alimb = a->d[i];
101#if BYTES_PER_MPI_LIMB == 4
102 *p++ = alimb >> 24;
103 *p++ = alimb >> 16;
104 *p++ = alimb >> 8;
105 *p++ = alimb;
106#elif BYTES_PER_MPI_LIMB == 8
107 *p++ = alimb >> 56;
108 *p++ = alimb >> 48;
109 *p++ = alimb >> 40;
110 *p++ = alimb >> 32;
111 *p++ = alimb >> 24;
112 *p++ = alimb >> 16;
113 *p++ = alimb >> 8;
114 *p++ = alimb;
115#else
116#error please implement for this limb size.
117#endif
118 }
119
120 /* this is sub-optimal but we need to do the shift operation
121 * because the caller has to free the returned buffer */
122 for (p = buffer; !*p && *nbytes; p++, --*nbytes)
123 ;
124 if (p != buffer)
125 memmove(buffer, p, *nbytes);
126
127 return buffer;
128}
129EXPORT_SYMBOL_GPL(mpi_get_buffer);
130
131/****************
132 * Use BUFFER to update MPI.
133 */
134int mpi_set_buffer(MPI a, const void *xbuffer, unsigned nbytes, int sign)
135{
136 const uint8_t *buffer = xbuffer, *p;
137 mpi_limb_t alimb;
138 int nlimbs;
139 int i;
140
141 nlimbs = (nbytes + BYTES_PER_MPI_LIMB - 1) / BYTES_PER_MPI_LIMB;
142 if (RESIZE_IF_NEEDED(a, nlimbs) < 0)
143 return -ENOMEM;
144 a->sign = sign;
145
146 for (i = 0, p = buffer + nbytes - 1; p >= buffer + BYTES_PER_MPI_LIMB;) {
147#if BYTES_PER_MPI_LIMB == 4
148 alimb = (mpi_limb_t) *p--;
149 alimb |= (mpi_limb_t) *p-- << 8;
150 alimb |= (mpi_limb_t) *p-- << 16;
151 alimb |= (mpi_limb_t) *p-- << 24;
152#elif BYTES_PER_MPI_LIMB == 8
153 alimb = (mpi_limb_t) *p--;
154 alimb |= (mpi_limb_t) *p-- << 8;
155 alimb |= (mpi_limb_t) *p-- << 16;
156 alimb |= (mpi_limb_t) *p-- << 24;
157 alimb |= (mpi_limb_t) *p-- << 32;
158 alimb |= (mpi_limb_t) *p-- << 40;
159 alimb |= (mpi_limb_t) *p-- << 48;
160 alimb |= (mpi_limb_t) *p-- << 56;
161#else
162#error please implement for this limb size.
163#endif
164 a->d[i++] = alimb;
165 }
166 if (p >= buffer) {
167#if BYTES_PER_MPI_LIMB == 4
168 alimb = *p--;
169 if (p >= buffer)
170 alimb |= (mpi_limb_t) *p-- << 8;
171 if (p >= buffer)
172 alimb |= (mpi_limb_t) *p-- << 16;
173 if (p >= buffer)
174 alimb |= (mpi_limb_t) *p-- << 24;
175#elif BYTES_PER_MPI_LIMB == 8
176 alimb = (mpi_limb_t) *p--;
177 if (p >= buffer)
178 alimb |= (mpi_limb_t) *p-- << 8;
179 if (p >= buffer)
180 alimb |= (mpi_limb_t) *p-- << 16;
181 if (p >= buffer)
182 alimb |= (mpi_limb_t) *p-- << 24;
183 if (p >= buffer)
184 alimb |= (mpi_limb_t) *p-- << 32;
185 if (p >= buffer)
186 alimb |= (mpi_limb_t) *p-- << 40;
187 if (p >= buffer)
188 alimb |= (mpi_limb_t) *p-- << 48;
189 if (p >= buffer)
190 alimb |= (mpi_limb_t) *p-- << 56;
191#else
192#error please implement for this limb size.
193#endif
194 a->d[i++] = alimb;
195 }
196 a->nlimbs = i;
197
198 if (i != nlimbs) {
199 pr_emerg("MPI: mpi_set_buffer: Assertion failed (%d != %d)", i,
200 nlimbs);
201 BUG();
202 }
203 return 0;
204}
205EXPORT_SYMBOL_GPL(mpi_set_buffer);