LXR linux/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 * mpi_read_buffer() - read MPI to a bufer provided by user (msb first)
 133 *
 134 * @a:          a multi precision integer
 135 * @buf:        bufer to which the output will be written to. Needs to be at
 136 *              leaset mpi_get_size(a) long.
 137 * @buf_len:    size of the buf.
 138 * @nbytes:     receives the actual length of the data written.
 139 * @sign:       if not NULL, it will be set to the sign of a.
 140 *
 141 * Return:      0 on success or error code in case of error
 142 */
 143int mpi_read_buffer(MPI a, uint8_t *buf, unsigned buf_len, unsigned *nbytes,
 144                    int *sign)
 145{
 146        uint8_t *p;
 147        mpi_limb_t alimb;
 148        unsigned int n = mpi_get_size(a);
 149        int i, lzeros = 0;
 150
 151        if (buf_len < n || !buf || !nbytes)
 152                return -EINVAL;
 153
 154        if (sign)
 155                *sign = a->sign;
 156
 157        p = (void *)&a->d[a->nlimbs] - 1;
 158
 159        for (i = a->nlimbs * sizeof(alimb) - 1; i >= 0; i--, p--) {
 160                if (!*p)
 161                        lzeros++;
 162                else
 163                        break;
 164        }
 165
 166        p = buf;
 167        *nbytes = n - lzeros;
 168
 169        for (i = a->nlimbs - 1; i >= 0; i--) {
 170                alimb = a->d[i];
 171#if BYTES_PER_MPI_LIMB == 4
 172                *p++ = alimb >> 24;
 173                *p++ = alimb >> 16;
 174                *p++ = alimb >> 8;
 175                *p++ = alimb;
 176#elif BYTES_PER_MPI_LIMB == 8
 177                *p++ = alimb >> 56;
 178                *p++ = alimb >> 48;
 179                *p++ = alimb >> 40;
 180                *p++ = alimb >> 32;
 181                *p++ = alimb >> 24;
 182                *p++ = alimb >> 16;
 183                *p++ = alimb >> 8;
 184                *p++ = alimb;
 185#else
 186#error please implement for this limb size.
 187#endif
 188
 189                if (lzeros > 0) {
 190                        if (lzeros >= sizeof(alimb)) {
 191                                p -= sizeof(alimb);
 192                        } else {
 193                                mpi_limb_t *limb1 = (void *)p - sizeof(alimb);
 194                                mpi_limb_t *limb2 = (void *)p - sizeof(alimb)
 195                                                        + lzeros;
 196                                *limb1 = *limb2;
 197                                p -= lzeros;
 198                        }
 199                        lzeros -= sizeof(alimb);
 200                }
 201        }
 202        return 0;
 203}
 204EXPORT_SYMBOL_GPL(mpi_read_buffer);
 205
 206/*
 207 * mpi_get_buffer() - Returns an allocated buffer with the MPI (msb first).
 208 * Caller must free the return string.
 209 * This function does return a 0 byte buffer with nbytes set to zero if the
 210 * value of A is zero.
 211 *
 212 * @a:          a multi precision integer.
 213 * @nbytes:     receives the length of this buffer.
 214 * @sign:       if not NULL, it will be set to the sign of the a.
 215 *
 216 * Return:      Pointer to MPI buffer or NULL on error
 217 */
 218void *mpi_get_buffer(MPI a, unsigned *nbytes, int *sign)
 219{
 220        uint8_t *buf;
 221        unsigned int n;
 222        int ret;
 223
 224        if (!nbytes)
 225                return NULL;
 226
 227        n = mpi_get_size(a);
 228
 229        if (!n)
 230                n++;
 231
 232        buf = kmalloc(n, GFP_KERNEL);
 233
 234        if (!buf)
 235                return NULL;
 236
 237        ret = mpi_read_buffer(a, buf, n, nbytes, sign);
 238
 239        if (ret) {
 240                kfree(buf);
 241                return NULL;
 242        }
 243        return buf;
 244}
 245EXPORT_SYMBOL_GPL(mpi_get_buffer);
 246
 247/****************
 248 * Use BUFFER to update MPI.
 249 */
 250int mpi_set_buffer(MPI a, const void *xbuffer, unsigned nbytes, int sign)
 251{
 252        const uint8_t *buffer = xbuffer, *p;
 253        mpi_limb_t alimb;
 254        int nlimbs;
 255        int i;
 256
 257        nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
 258        if (RESIZE_IF_NEEDED(a, nlimbs) < 0)
 259                return -ENOMEM;
 260        a->sign = sign;
 261
 262        for (i = 0, p = buffer + nbytes - 1; p >= buffer + BYTES_PER_MPI_LIMB;) {
 263#if BYTES_PER_MPI_LIMB == 4
 264                alimb = (mpi_limb_t) *p--;
 265                alimb |= (mpi_limb_t) *p-- << 8;
 266                alimb |= (mpi_limb_t) *p-- << 16;
 267                alimb |= (mpi_limb_t) *p-- << 24;
 268#elif BYTES_PER_MPI_LIMB == 8
 269                alimb = (mpi_limb_t) *p--;
 270                alimb |= (mpi_limb_t) *p-- << 8;
 271                alimb |= (mpi_limb_t) *p-- << 16;
 272                alimb |= (mpi_limb_t) *p-- << 24;
 273                alimb |= (mpi_limb_t) *p-- << 32;
 274                alimb |= (mpi_limb_t) *p-- << 40;
 275                alimb |= (mpi_limb_t) *p-- << 48;
 276                alimb |= (mpi_limb_t) *p-- << 56;
 277#else
 278#error please implement for this limb size.
 279#endif
 280                a->d[i++] = alimb;
 281        }
 282        if (p >= buffer) {
 283#if BYTES_PER_MPI_LIMB == 4
 284                alimb = *p--;
 285                if (p >= buffer)
 286                        alimb |= (mpi_limb_t) *p-- << 8;
 287                if (p >= buffer)
 288                        alimb |= (mpi_limb_t) *p-- << 16;
 289                if (p >= buffer)
 290                        alimb |= (mpi_limb_t) *p-- << 24;
 291#elif BYTES_PER_MPI_LIMB == 8
 292                alimb = (mpi_limb_t) *p--;
 293                if (p >= buffer)
 294                        alimb |= (mpi_limb_t) *p-- << 8;
 295                if (p >= buffer)
 296                        alimb |= (mpi_limb_t) *p-- << 16;
 297                if (p >= buffer)
 298                        alimb |= (mpi_limb_t) *p-- << 24;
 299                if (p >= buffer)
 300                        alimb |= (mpi_limb_t) *p-- << 32;
 301                if (p >= buffer)
 302                        alimb |= (mpi_limb_t) *p-- << 40;
 303                if (p >= buffer)
 304                        alimb |= (mpi_limb_t) *p-- << 48;
 305                if (p >= buffer)
 306                        alimb |= (mpi_limb_t) *p-- << 56;
 307#else
 308#error please implement for this limb size.
 309#endif
 310                a->d[i++] = alimb;
 311        }
 312        a->nlimbs = i;
 313
 314        if (i != nlimbs) {
 315                pr_emerg("MPI: mpi_set_buffer: Assertion failed (%d != %d)", i,
 316                       nlimbs);
 317                BUG();
 318        }
 319        return 0;
 320}
 321EXPORT_SYMBOL_GPL(mpi_set_buffer);
 322