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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 <linux/bitops.h>
22#include <asm-generic/bitops/count_zeros.h>
23#include "mpi-internal.h"
24
25#define MAX_EXTERN_MPI_BITS 16384
26
27/**
28 * mpi_read_raw_data - Read a raw byte stream as a positive integer
29 * @xbuffer: The data to read
30 * @nbytes: The amount of data to read
31 */
32MPI mpi_read_raw_data(const void *xbuffer, size_t nbytes)
33{
34 const uint8_t *buffer = xbuffer;
35 int i, j;
36 unsigned nbits, nlimbs;
37 mpi_limb_t a;
38 MPI val = NULL;
39
40 while (nbytes > 0 && buffer[0] == 0) {
41 buffer++;
42 nbytes--;
43 }
44
45 nbits = nbytes * 8;
46 if (nbits > MAX_EXTERN_MPI_BITS) {
47 pr_info("MPI: mpi too large (%u bits)\n", nbits);
48 return NULL;
49 }
50 if (nbytes > 0)
51 nbits -= count_leading_zeros(buffer[0]);
52 else
53 nbits = 0;
54
55 nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
56 val = mpi_alloc(nlimbs);
57 if (!val)
58 return NULL;
59 val->nbits = nbits;
60 val->sign = 0;
61 val->nlimbs = nlimbs;
62
63 if (nbytes > 0) {
64 i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
65 i %= BYTES_PER_MPI_LIMB;
66 for (j = nlimbs; j > 0; j--) {
67 a = 0;
68 for (; i < BYTES_PER_MPI_LIMB; i++) {
69 a <<= 8;
70 a |= *buffer++;
71 }
72 i = 0;
73 val->d[j - 1] = a;
74 }
75 }
76 return val;
77}
78EXPORT_SYMBOL_GPL(mpi_read_raw_data);
79
80MPI mpi_read_from_buffer(const void *xbuffer, unsigned *ret_nread)
81{
82 const uint8_t *buffer = xbuffer;
83 int i, j;
84 unsigned nbits, nbytes, nlimbs, nread = 0;
85 mpi_limb_t a;
86 MPI val = NULL;
87
88 if (*ret_nread < 2)
89 goto leave;
90 nbits = buffer[0] << 8 | buffer[1];
91
92 if (nbits > MAX_EXTERN_MPI_BITS) {
93 pr_info("MPI: mpi too large (%u bits)\n", nbits);
94 goto leave;
95 }
96 buffer += 2;
97 nread = 2;
98
99 nbytes = DIV_ROUND_UP(nbits, 8);
100 nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
101 val = mpi_alloc(nlimbs);
102 if (!val)
103 return NULL;
104 i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
105 i %= BYTES_PER_MPI_LIMB;
106 val->nbits = nbits;
107 j = val->nlimbs = nlimbs;
108 val->sign = 0;
109 for (; j > 0; j--) {
110 a = 0;
111 for (; i < BYTES_PER_MPI_LIMB; i++) {
112 if (++nread > *ret_nread) {
113 printk
114 ("MPI: mpi larger than buffer nread=%d ret_nread=%d\n",
115 nread, *ret_nread);
116 goto leave;
117 }
118 a <<= 8;
119 a |= *buffer++;
120 }
121 i = 0;
122 val->d[j - 1] = a;
123 }
124
125leave:
126 *ret_nread = nread;
127 return val;
128}
129EXPORT_SYMBOL_GPL(mpi_read_from_buffer);
130
131/****************
132 * Return an allocated buffer with the MPI (msb first).
133 * NBYTES receives the length of this buffer. Caller must free the
134 * return string (This function does return a 0 byte buffer with NBYTES
135 * set to zero if the value of A is zero. If sign is not NULL, it will
136 * be set to the sign of the A.
137 */
138void *mpi_get_buffer(MPI a, unsigned *nbytes, int *sign)
139{
140 uint8_t *p, *buffer;
141 mpi_limb_t alimb;
142 int i;
143 unsigned int n;
144
145 if (sign)
146 *sign = a->sign;
147 *nbytes = n = a->nlimbs * BYTES_PER_MPI_LIMB;
148 if (!n)
149 n++; /* avoid zero length allocation */
150 p = buffer = kmalloc(n, GFP_KERNEL);
151 if (!p)
152 return NULL;
153
154 for (i = a->nlimbs - 1; i >= 0; i--) {
155 alimb = a->d[i];
156#if BYTES_PER_MPI_LIMB == 4
157 *p++ = alimb >> 24;
158 *p++ = alimb >> 16;
159 *p++ = alimb >> 8;
160 *p++ = alimb;
161#elif BYTES_PER_MPI_LIMB == 8
162 *p++ = alimb >> 56;
163 *p++ = alimb >> 48;
164 *p++ = alimb >> 40;
165 *p++ = alimb >> 32;
166 *p++ = alimb >> 24;
167 *p++ = alimb >> 16;
168 *p++ = alimb >> 8;
169 *p++ = alimb;
170#else
171#error please implement for this limb size.
172#endif
173 }
174
175 /* this is sub-optimal but we need to do the shift operation
176 * because the caller has to free the returned buffer */
177 for (p = buffer; !*p && *nbytes; p++, --*nbytes)
178 ;
179 if (p != buffer)
180 memmove(buffer, p, *nbytes);
181
182 return buffer;
183}
184EXPORT_SYMBOL_GPL(mpi_get_buffer);
185
186/****************
187 * Use BUFFER to update MPI.
188 */
189int mpi_set_buffer(MPI a, const void *xbuffer, unsigned nbytes, int sign)
190{
191 const uint8_t *buffer = xbuffer, *p;
192 mpi_limb_t alimb;
193 int nlimbs;
194 int i;
195
196 nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
197 if (RESIZE_IF_NEEDED(a, nlimbs) < 0)
198 return -ENOMEM;
199 a->sign = sign;
200
201 for (i = 0, p = buffer + nbytes - 1; p >= buffer + BYTES_PER_MPI_LIMB;) {
202#if BYTES_PER_MPI_LIMB == 4
203 alimb = (mpi_limb_t) *p--;
204 alimb |= (mpi_limb_t) *p-- << 8;
205 alimb |= (mpi_limb_t) *p-- << 16;
206 alimb |= (mpi_limb_t) *p-- << 24;
207#elif BYTES_PER_MPI_LIMB == 8
208 alimb = (mpi_limb_t) *p--;
209 alimb |= (mpi_limb_t) *p-- << 8;
210 alimb |= (mpi_limb_t) *p-- << 16;
211 alimb |= (mpi_limb_t) *p-- << 24;
212 alimb |= (mpi_limb_t) *p-- << 32;
213 alimb |= (mpi_limb_t) *p-- << 40;
214 alimb |= (mpi_limb_t) *p-- << 48;
215 alimb |= (mpi_limb_t) *p-- << 56;
216#else
217#error please implement for this limb size.
218#endif
219 a->d[i++] = alimb;
220 }
221 if (p >= buffer) {
222#if BYTES_PER_MPI_LIMB == 4
223 alimb = *p--;
224 if (p >= buffer)
225 alimb |= (mpi_limb_t) *p-- << 8;
226 if (p >= buffer)
227 alimb |= (mpi_limb_t) *p-- << 16;
228 if (p >= buffer)
229 alimb |= (mpi_limb_t) *p-- << 24;
230#elif BYTES_PER_MPI_LIMB == 8
231 alimb = (mpi_limb_t) *p--;
232 if (p >= buffer)
233 alimb |= (mpi_limb_t) *p-- << 8;
234 if (p >= buffer)
235 alimb |= (mpi_limb_t) *p-- << 16;
236 if (p >= buffer)
237 alimb |= (mpi_limb_t) *p-- << 24;
238 if (p >= buffer)
239 alimb |= (mpi_limb_t) *p-- << 32;
240 if (p >= buffer)
241 alimb |= (mpi_limb_t) *p-- << 40;
242 if (p >= buffer)
243 alimb |= (mpi_limb_t) *p-- << 48;
244 if (p >= buffer)
245 alimb |= (mpi_limb_t) *p-- << 56;
246#else
247#error please implement for this limb size.
248#endif
249 a->d[i++] = alimb;
250 }
251 a->nlimbs = i;
252
253 if (i != nlimbs) {
254 pr_emerg("MPI: mpi_set_buffer: Assertion failed (%d != %d)", i,
255 nlimbs);
256 BUG();
257 }
258 return 0;
259}
260EXPORT_SYMBOL_GPL(mpi_set_buffer);