/* 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 <linux/byteorder/generic.h>
#include <linux/count_zeros.h>
#include <linux/export.h>
#include <linux/scatterlist.h>
#include <linux/string.h>
#include "mpi-internal.h"

#define MAX_EXTERN_MPI_BITS 16384

/**
 * mpi_read_raw_data - Read a raw byte stream as a positive integer
 * @xbuffer: The data to read
 * @nbytes: The amount of data to read
 */
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]) - (BITS_PER_LONG - 8);

        nlimbs = DIV_ROUND_UP(nbytes, 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;
        unsigned int nbits, nbytes;
        MPI val;

        if (*ret_nread < 2)
                return ERR_PTR(-EINVAL);
        nbits = buffer[0] << 8 | buffer[1];

        if (nbits > MAX_EXTERN_MPI_BITS) {
                pr_info("MPI: mpi too large (%u bits)\n", nbits);
                return ERR_PTR(-EINVAL);
        }

        nbytes = DIV_ROUND_UP(nbits, 8);
        if (nbytes + 2 > *ret_nread) {
                pr_info("MPI: mpi larger than buffer nbytes=%u ret_nread=%u\n",
                                nbytes, *ret_nread);
                return ERR_PTR(-EINVAL);
        }

        val = mpi_read_raw_data(buffer + 2, nbytes);
        if (!val)
                return ERR_PTR(-ENOMEM);

        *ret_nread = nbytes + 2;
        return val;
}
EXPORT_SYMBOL_GPL(mpi_read_from_buffer);

static int count_lzeros(MPI a)
{
        mpi_limb_t alimb;
        int i, lzeros = 0;

        for (i = a->nlimbs - 1; i >= 0; i--) {
                alimb = a->d[i];
                if (alimb == 0) {
                        lzeros += sizeof(mpi_limb_t);
                } else {
                        lzeros += count_leading_zeros(alimb) / 8;
                        break;
                }
        }
        return lzeros;
}

/**
 * mpi_read_buffer() - read MPI to a buffer provided by user (msb first)
 *
 * @a:          a multi precision integer
 * @buf:        buffer to which the output will be written to. Needs to be at
 *              least mpi_get_size(a) long.
 * @buf_len:    size of the buf.
 * @nbytes:     receives the actual length of the data written on success and
 *              the data to-be-written on -EOVERFLOW in case buf_len was too
 *              small.
 * @sign:       if not NULL, it will be set to the sign of a.
 *
 * Return:      0 on success or error code in case of error
 */
int mpi_read_buffer(MPI a, uint8_t *buf, unsigned buf_len, unsigned *nbytes,
                    int *sign)
{
        uint8_t *p;
#if BYTES_PER_MPI_LIMB == 4
        __be32 alimb;
#elif BYTES_PER_MPI_LIMB == 8
        __be64 alimb;
#else
#error please implement for this limb size.
#endif
        unsigned int n = mpi_get_size(a);
        int i, lzeros;

        if (!buf || !nbytes)
                return -EINVAL;

        if (sign)
                *sign = a->sign;

        lzeros = count_lzeros(a);

        if (buf_len < n - lzeros) {
                *nbytes = n - lzeros;
                return -EOVERFLOW;
        }

        p = buf;
        *nbytes = n - lzeros;

        for (i = a->nlimbs - 1 - lzeros / BYTES_PER_MPI_LIMB,
                        lzeros %= BYTES_PER_MPI_LIMB;
                i >= 0; i--) {
#if BYTES_PER_MPI_LIMB == 4
                alimb = cpu_to_be32(a->d[i]);
#elif BYTES_PER_MPI_LIMB == 8
                alimb = cpu_to_be64(a->d[i]);
#else
#error please implement for this limb size.
#endif
                memcpy(p, (u8 *)&alimb + lzeros, BYTES_PER_MPI_LIMB - lzeros);
                p += BYTES_PER_MPI_LIMB - lzeros;
                lzeros = 0;
        }
        return 0;
}
EXPORT_SYMBOL_GPL(mpi_read_buffer);

/*
 * mpi_get_buffer() - Returns an allocated buffer with the MPI (msb first).
 * 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.
 *
 * @a:          a multi precision integer.
 * @nbytes:     receives the length of this buffer.
 * @sign:       if not NULL, it will be set to the sign of the a.
 *
 * Return:      Pointer to MPI buffer or NULL on error
 */
void *mpi_get_buffer(MPI a, unsigned *nbytes, int *sign)
{
        uint8_t *buf;
        unsigned int n;
        int ret;

        if (!nbytes)
                return NULL;

        n = mpi_get_size(a);

        if (!n)
                n++;

        buf = kmalloc(n, GFP_KERNEL);

        if (!buf)
                return NULL;

        ret = mpi_read_buffer(a, buf, n, nbytes, sign);

        if (ret) {
                kfree(buf);
                return NULL;
        }
        return buf;
}
EXPORT_SYMBOL_GPL(mpi_get_buffer);

/**
 * mpi_write_to_sgl() - Funnction exports MPI to an sgl (msb first)
 *
 * This function works in the same way as the mpi_read_buffer, but it
 * takes an sgl instead of u8 * buf.
 *
 * @a:          a multi precision integer
 * @sgl:        scatterlist to write to. Needs to be at least
 *              mpi_get_size(a) long.
 * @nbytes:     the number of bytes to write.  Leading bytes will be
 *              filled with zero.
 * @sign:       if not NULL, it will be set to the sign of a.
 *
 * Return:      0 on success or error code in case of error
 */
int mpi_write_to_sgl(MPI a, struct scatterlist *sgl, unsigned nbytes,
                     int *sign)
{
        u8 *p, *p2;
#if BYTES_PER_MPI_LIMB == 4
        __be32 alimb;
#elif BYTES_PER_MPI_LIMB == 8
        __be64 alimb;
#else
#error please implement for this limb size.
#endif
        unsigned int n = mpi_get_size(a);
        struct sg_mapping_iter miter;
        int i, x, buf_len;
        int nents;

        if (sign)
                *sign = a->sign;

        if (nbytes < n)
                return -EOVERFLOW;

        nents = sg_nents_for_len(sgl, nbytes);
        if (nents < 0)
                return -EINVAL;

        sg_miter_start(&miter, sgl, nents, SG_MITER_ATOMIC | SG_MITER_TO_SG);
        sg_miter_next(&miter);
        buf_len = miter.length;
        p2 = miter.addr;

        while (nbytes > n) {
                i = min_t(unsigned, nbytes - n, buf_len);
                memset(p2, 0, i);
                p2 += i;
                nbytes -= i;

                buf_len -= i;
                if (!buf_len) {
                        sg_miter_next(&miter);
                        buf_len = miter.length;
                        p2 = miter.addr;
                }
        }

        for (i = a->nlimbs - 1; i >= 0; i--) {
#if BYTES_PER_MPI_LIMB == 4
                alimb = a->d[i] ? cpu_to_be32(a->d[i]) : 0;
#elif BYTES_PER_MPI_LIMB == 8
                alimb = a->d[i] ? cpu_to_be64(a->d[i]) : 0;
#else
#error please implement for this limb size.
#endif
                p = (u8 *)&alimb;

                for (x = 0; x < sizeof(alimb); x++) {
                        *p2++ = *p++;
                        if (!--buf_len) {
                                sg_miter_next(&miter);
                                buf_len = miter.length;
                                p2 = miter.addr;
                        }
                }
        }

        sg_miter_stop(&miter);
        return 0;
}
EXPORT_SYMBOL_GPL(mpi_write_to_sgl);

/*
 * mpi_read_raw_from_sgl() - Function allocates an MPI and populates it with
 *                           data from the sgl
 *
 * This function works in the same way as the mpi_read_raw_data, but it
 * takes an sgl instead of void * buffer. i.e. it allocates
 * a new MPI and reads the content of the sgl to the MPI.
 *
 * @sgl:        scatterlist to read from
 * @nbytes:     number of bytes to read
 *
 * Return:      Pointer to a new MPI or NULL on error
 */
MPI mpi_read_raw_from_sgl(struct scatterlist *sgl, unsigned int nbytes)
{
        struct sg_mapping_iter miter;
        unsigned int nbits, nlimbs;
        int x, j, z, lzeros, ents;
        unsigned int len;
        const u8 *buff;
        mpi_limb_t a;
        MPI val = NULL;

        ents = sg_nents_for_len(sgl, nbytes);
        if (ents < 0)
                return NULL;

        sg_miter_start(&miter, sgl, ents, SG_MITER_ATOMIC | SG_MITER_FROM_SG);

        lzeros = 0;
        len = 0;
        while (nbytes > 0) {
                while (len && !*buff) {
                        lzeros++;
                        len--;
                        buff++;
                }

                if (len && *buff)
                        break;

                sg_miter_next(&miter);
                buff = miter.addr;
                len = miter.length;

                nbytes -= lzeros;
                lzeros = 0;
        }

        miter.consumed = lzeros;

        nbytes -= lzeros;
        nbits = nbytes * 8;
        if (nbits > MAX_EXTERN_MPI_BITS) {
                sg_miter_stop(&miter);
                pr_info("MPI: mpi too large (%u bits)\n", nbits);
                return NULL;
        }

        if (nbytes > 0)
                nbits -= count_leading_zeros(*buff) - (BITS_PER_LONG - 8);

        sg_miter_stop(&miter);

        nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
        val = mpi_alloc(nlimbs);
        if (!val)
                return NULL;

        val->nbits = nbits;
        val->sign = 0;
        val->nlimbs = nlimbs;

        if (nbytes == 0)
                return val;

        j = nlimbs - 1;
        a = 0;
        z = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
        z %= BYTES_PER_MPI_LIMB;

        while (sg_miter_next(&miter)) {
                buff = miter.addr;
                len = min(miter.length, nbytes);
                nbytes -= len;

                for (x = 0; x < len; x++) {
                        a <<= 8;
                        a |= *buff++;
                        if (((z + x + 1) % BYTES_PER_MPI_LIMB) == 0) {
                                val->d[j--] = a;
                                a = 0;
                        }
                }
                z += x;
        }

        return val;
}
EXPORT_SYMBOL_GPL(mpi_read_raw_from_sgl);