Root/lib/mpi/mpicoder.c

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);
261

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