/* 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_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)
  ", nbits);
  		return NULL;
  	}
  	if (nbytes > 0)
  		nbits -= count_leading_zeros(buffer[0]);
  	else
  		nbits = 0;
  
  	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;
  	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)
  ", nbits);
  		goto leave;
  	}
  	buffer += 2;
  	nread = 2;
  
  	nbytes = DIV_ROUND_UP(nbits, 8);
  	nlimbs = DIV_ROUND_UP(nbytes, 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
  ",
  				     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 = DIV_ROUND_UP(nbytes, 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);