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  */
  32 MPI 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 }
  78 EXPORT_SYMBOL_GPL(mpi_read_raw_data);
  79
  80 MPI 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
 125 leave:
 126         *ret_nread = nread;
 127         return val;
 128 }
 129 EXPORT_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  */
 138 void *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 }
 184 EXPORT_SYMBOL_GPL(mpi_get_buffer);
 185
 186 /****************
 187  * Use BUFFER to update MPI.
 188  */
 189 int 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 }
 260 EXPORT_SYMBOL_GPL(mpi_set_buffer);