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 "mpi-internal.h"
  22
  23 #define MAX_EXTERN_MPI_BITS 16384
  24
  25 MPI 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
  70 leave:
  71         *ret_nread = nread;
  72         return val;
  73 }
  74 EXPORT_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  */
  83 void *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 }
 129 EXPORT_SYMBOL_GPL(mpi_get_buffer);
 130
 131 /****************
 132  * Use BUFFER to update MPI.
 133  */
 134 int 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 }
 205 EXPORT_SYMBOL_GPL(mpi_set_buffer);