mpicoder.c

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/* mpicoder.c  -  Coder for the external representation of MPIs
 * Copyright (C) 1998, 1999 Free Software Foundation, Inc.
 *
 * This file is part of GnuPG.
 *
 * GnuPG is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * GnuPG is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
 */

#include <linux/bitops.h>
#include <asm-generic/bitops/count_zeros.h>
#include "mpi-internal.h"

#define MAX_EXTERN_MPI_BITS 16384

MPI mpi_read_raw_data(const void *xbuffer, size_t nbytes)
{
    const uint8_t *buffer = xbuffer;
    int i, j;
    unsigned nbits, nlimbs;
    mpi_limb_t a;
    MPI val = NULL;

    while (nbytes >= 0 && buffer[0] == 0) {
        buffer++;
        nbytes--;
    }

    nbits = nbytes * 8;
    if (nbits > MAX_EXTERN_MPI_BITS) {
        pr_info("MPI: mpi too large (%u bits)\n", nbits);
        return NULL;
    }
    if (nbytes > 0)
        nbits -= count_leading_zeros(buffer[0]);
    else
        nbits = 0;

    nlimbs = (nbytes + BYTES_PER_MPI_LIMB - 1) / BYTES_PER_MPI_LIMB;
    val = mpi_alloc(nlimbs);
    if (!val)
        return NULL;
    val->nbits = nbits;
    val->sign = 0;
    val->nlimbs = nlimbs;

    if (nbytes > 0) {
        i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
        i %= BYTES_PER_MPI_LIMB;
        for (j = nlimbs; j > 0; j--) {
            a = 0;
            for (; i < BYTES_PER_MPI_LIMB; i++) {
                a <<= 8;
                a |= *buffer++;
            }
            i = 0;
            val->d[j - 1] = a;
        }
    }
    return val;
}
EXPORT_SYMBOL_GPL(mpi_read_raw_data);

MPI mpi_read_from_buffer(const void *xbuffer, unsigned *ret_nread)
{
    const uint8_t *buffer = xbuffer;
    int i, j;
    unsigned nbits, nbytes, nlimbs, nread = 0;
    mpi_limb_t a;
    MPI val = NULL;

    if (*ret_nread < 2)
        goto leave;
    nbits = buffer[0] << 8 | buffer[1];

    if (nbits > MAX_EXTERN_MPI_BITS) {
        pr_info("MPI: mpi too large (%u bits)\n", nbits);
        goto leave;
    }
    buffer += 2;
    nread = 2;

    nbytes = (nbits + 7) / 8;
    nlimbs = (nbytes + BYTES_PER_MPI_LIMB - 1) / BYTES_PER_MPI_LIMB;
    val = mpi_alloc(nlimbs);
    if (!val)
        return NULL;
    i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
    i %= BYTES_PER_MPI_LIMB;
    val->nbits = nbits;
    j = val->nlimbs = nlimbs;
    val->sign = 0;
    for (; j > 0; j--) {
        a = 0;
        for (; i < BYTES_PER_MPI_LIMB; i++) {
            if (++nread > *ret_nread) {
                printk
                    ("MPI: mpi larger than buffer nread=%d ret_nread=%d\n",
                     nread, *ret_nread);
                goto leave;
            }
            a <<= 8;
            a |= *buffer++;
        }
        i = 0;
        val->d[j - 1] = a;
    }

leave:
    *ret_nread = nread;
    return val;
}
EXPORT_SYMBOL_GPL(mpi_read_from_buffer);

/****************
 * Return an allocated buffer with the MPI (msb first).
 * NBYTES receives the length of this buffer. Caller must free the
 * return string (This function does return a 0 byte buffer with NBYTES
 * set to zero if the value of A is zero. If sign is not NULL, it will
 * be set to the sign of the A.
 */
void *mpi_get_buffer(MPI a, unsigned *nbytes, int *sign)
{
    uint8_t *p, *buffer;
    mpi_limb_t alimb;
    int i;
    unsigned int n;

    if (sign)
        *sign = a->sign;
    *nbytes = n = a->nlimbs * BYTES_PER_MPI_LIMB;
    if (!n)
        n++;        /* avoid zero length allocation */
    p = buffer = kmalloc(n, GFP_KERNEL);
    if (!p)
        return NULL;

    for (i = a->nlimbs - 1; i >= 0; i--) {
        alimb = a->d[i];
#if BYTES_PER_MPI_LIMB == 4
        *p++ = alimb >> 24;
        *p++ = alimb >> 16;
        *p++ = alimb >> 8;
        *p++ = alimb;
#elif BYTES_PER_MPI_LIMB == 8
        *p++ = alimb >> 56;
        *p++ = alimb >> 48;
        *p++ = alimb >> 40;
        *p++ = alimb >> 32;
        *p++ = alimb >> 24;
        *p++ = alimb >> 16;
        *p++ = alimb >> 8;
        *p++ = alimb;
#else
#error please implement for this limb size.
#endif
    }

    /* this is sub-optimal but we need to do the shift operation
     * because the caller has to free the returned buffer */
    for (p = buffer; !*p && *nbytes; p++, --*nbytes)
        ;
    if (p != buffer)
        memmove(buffer, p, *nbytes);

    return buffer;
}
EXPORT_SYMBOL_GPL(mpi_get_buffer);

/****************
 * Use BUFFER to update MPI.
 */
int mpi_set_buffer(MPI a, const void *xbuffer, unsigned nbytes, int sign)
{
    const uint8_t *buffer = xbuffer, *p;
    mpi_limb_t alimb;
    int nlimbs;
    int i;

    nlimbs = (nbytes + BYTES_PER_MPI_LIMB - 1) / BYTES_PER_MPI_LIMB;
    if (RESIZE_IF_NEEDED(a, nlimbs) < 0)
        return -ENOMEM;
    a->sign = sign;

    for (i = 0, p = buffer + nbytes - 1; p >= buffer + BYTES_PER_MPI_LIMB;) {
#if BYTES_PER_MPI_LIMB == 4
        alimb = (mpi_limb_t) *p--;
        alimb |= (mpi_limb_t) *p-- << 8;
        alimb |= (mpi_limb_t) *p-- << 16;
        alimb |= (mpi_limb_t) *p-- << 24;
#elif BYTES_PER_MPI_LIMB == 8
        alimb = (mpi_limb_t) *p--;
        alimb |= (mpi_limb_t) *p-- << 8;
        alimb |= (mpi_limb_t) *p-- << 16;
        alimb |= (mpi_limb_t) *p-- << 24;
        alimb |= (mpi_limb_t) *p-- << 32;
        alimb |= (mpi_limb_t) *p-- << 40;
        alimb |= (mpi_limb_t) *p-- << 48;
        alimb |= (mpi_limb_t) *p-- << 56;
#else
#error please implement for this limb size.
#endif
        a->d[i++] = alimb;
    }
    if (p >= buffer) {
#if BYTES_PER_MPI_LIMB == 4
        alimb = *p--;
        if (p >= buffer)
            alimb |= (mpi_limb_t) *p-- << 8;
        if (p >= buffer)
            alimb |= (mpi_limb_t) *p-- << 16;
        if (p >= buffer)
            alimb |= (mpi_limb_t) *p-- << 24;
#elif BYTES_PER_MPI_LIMB == 8
        alimb = (mpi_limb_t) *p--;
        if (p >= buffer)
            alimb |= (mpi_limb_t) *p-- << 8;
        if (p >= buffer)
            alimb |= (mpi_limb_t) *p-- << 16;
        if (p >= buffer)
            alimb |= (mpi_limb_t) *p-- << 24;
        if (p >= buffer)
            alimb |= (mpi_limb_t) *p-- << 32;
        if (p >= buffer)
            alimb |= (mpi_limb_t) *p-- << 40;
        if (p >= buffer)
            alimb |= (mpi_limb_t) *p-- << 48;
        if (p >= buffer)
            alimb |= (mpi_limb_t) *p-- << 56;
#else
#error please implement for this limb size.
#endif
        a->d[i++] = alimb;
    }
    a->nlimbs = i;

    if (i != nlimbs) {
        pr_emerg("MPI: mpi_set_buffer: Assertion failed (%d != %d)", i,
               nlimbs);
        BUG();
    }
    return 0;
}
EXPORT_SYMBOL_GPL(mpi_set_buffer);