linux/lib/mpi/mpicoder.c
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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 = (nbytes + BYTES_PER_MPI_LIMB - 1) / 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 = (nbits + 7) / 8;
 100        nlimbs = (nbytes + BYTES_PER_MPI_LIMB - 1) / 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 = (nbytes + BYTES_PER_MPI_LIMB - 1) / 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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