/*

 * Checksum functions

 *

 * Copyright (C) 2009-2024, Joachim Metz <joachim.metz@gmail.com>

 *

 * Refer to AUTHORS for acknowledgements.

 *

 * This program is free software: you can redistribute it and/or modify

 * it under the terms of the GNU Lesser General Public License as published by

 * the Free Software Foundation, either version 3 of the License, or

 * (at your option) any later version.

 *

 * This program 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 Lesser General Public License

 * along with this program.  If not, see <https://www.gnu.org/licenses/>.

 */

#include <common.h>

#include <byte_stream.h>

#include <types.h>

#include "libregf_checksum.h"

#include "libregf_libcerror.h"

/* The largest primary (or scalar) available

 * supported by a single load and store instruction

 */

typedef unsigned long int libregf_aligned_t;

/* Calculates the little-endian XOR-32 of a buffer

 * It uses the initial value to calculate a new XOR-32

 * Returns 1 if successful or -1 on error

 */

int libregf_checksum_calculate_little_endian_xor32(

     uint32_t *checksum_value,

     const uint8_t *buffer,

     size_t size,

     uint32_t initial_value,

     libcerror_error_t **error )

{

  libregf_aligned_t *aligned_buffer_iterator = NULL;

  uint8_t *buffer_iterator                   = NULL;

  static char *function                      = "libregf_checksum_calculate_little_endian_xor32";

  libregf_aligned_t value_aligned            = 0;

  uint32_t big_endian_value_32bit            = 0;

  uint32_t safe_checksum_value               = 0;

  uint32_t value_32bit                       = 0;

  uint8_t alignment_count                    = 0;

  uint8_t alignment_size                     = 0;

  uint8_t byte_count                         = 0;

  uint8_t byte_order                         = 0;

  uint8_t byte_size                          = 0;

  if( checksum_value == NULL )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_ARGUMENTS,

     LIBCERROR_ARGUMENT_ERROR_INVALID_VALUE,

     "%s: invalid checksum value.",

     function );

    return( -1 );

  }

  if( buffer == NULL )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_ARGUMENTS,

     LIBCERROR_ARGUMENT_ERROR_INVALID_VALUE,

     "%s: invalid buffer.",

     function );

    return( -1 );

  }

  if( size > (size_t) SSIZE_MAX )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_ARGUMENTS,

     LIBCERROR_ARGUMENT_ERROR_VALUE_EXCEEDS_MAXIMUM,

     "%s: invalid size value exceeds maximum.",

     function );

    return( -1 );

  }

  safe_checksum_value = initial_value;

  buffer_iterator = (uint8_t *) buffer;

  /* Only optimize when there is the alignment is a multitude of 32-bit

   * and for buffers larger than the alignment

   */

  if( ( ( sizeof( libregf_aligned_t ) % 4 ) == 0 )

   && ( size > ( 2 * sizeof( libregf_aligned_t ) ) ) )

  {

    /* Align the buffer iterator

     */

    alignment_size = (uint8_t) ( (intptr_t) buffer_iterator % sizeof( libregf_aligned_t ) );

    if( alignment_size > 0 )

    {

      byte_size = sizeof( libregf_aligned_t ) - alignment_size;

      /* Align the buffer iterator in 4-byte steps

       */

      while( byte_size != 0 )

      {

        value_32bit = 0;

        byte_count  = 1;

        if( byte_size >= 4 )

        {

          value_32bit |= buffer_iterator[ 3 ];

          value_32bit <<= 8;

          byte_count++;

        }

        if( byte_size >= 3 )

        {

          value_32bit |= buffer_iterator[ 2 ];

          value_32bit <<= 8;

          byte_count++;

        }

        if( byte_size >= 2 )

        {

          value_32bit |= buffer_iterator[ 1 ];

          value_32bit <<= 8;

          byte_count++;

        }

        value_32bit |= buffer_iterator[ 0 ];

        buffer_iterator += byte_count;

        byte_size       -= byte_count;

        safe_checksum_value ^= value_32bit;

      }

      size -= byte_count;

    }

    aligned_buffer_iterator = (libregf_aligned_t *) buffer_iterator;

    if( *buffer_iterator != (uint8_t) ( *aligned_buffer_iterator & 0xff ) )

    {

      byte_order = _BYTE_STREAM_ENDIAN_BIG;

    }

    else

    {

      byte_order = _BYTE_STREAM_ENDIAN_LITTLE;

    }

    /* Calculate the XOR value using the aligned buffer iterator

     */

    while( size > sizeof( libregf_aligned_t ) )

    {

      value_aligned ^= *aligned_buffer_iterator;

      aligned_buffer_iterator++;

      size -= sizeof( libregf_aligned_t );

    }

    /* Align the aligned XOR value with the 32-bit XOR value

     */

    if( alignment_size > 0 )

    {

      byte_count      = ( alignment_size % 4 ) * 8;

      alignment_count = ( sizeof( libregf_aligned_t ) - alignment_size ) * 8;

      if( byte_order == _BYTE_STREAM_ENDIAN_BIG )

      {

        /* Shift twice to set unused bytes to 0

         */

        big_endian_value_32bit = (uint32_t) ( ( value_aligned >> alignment_count ) << byte_count );

        /* Change big-endian into little-endian

         */

        value_32bit = ( ( big_endian_value_32bit & 0x000000ffUL ) << 24 )

                    | ( ( big_endian_value_32bit & 0x0000ff00UL ) << 8 )

                    | ( ( big_endian_value_32bit >> 8 ) & 0x0000ff00UL )

                    | ( ( big_endian_value_32bit >> 24 ) & 0x000000ffUL );

        /* Strip-off the used part of the aligned value

         */

        value_aligned <<= alignment_count;

      }

      else if( byte_order == _BYTE_STREAM_ENDIAN_LITTLE )

      {

        value_32bit = (uint32_t) ( value_aligned << byte_count );

        /* Strip-off the used part of the aligned value

         */

        value_aligned >>= alignment_count;

      }

      safe_checksum_value ^= value_32bit;

    }

    /* Update the 32-bit XOR value with the aligned XOR value

     */

    byte_size = (uint8_t) sizeof( libregf_aligned_t );

    while( byte_size != 0 )

    {

      byte_count = ( ( byte_size / 4 ) - 1 ) * 32;

      if( byte_order == _BYTE_STREAM_ENDIAN_BIG )

      {

        big_endian_value_32bit = (uint32_t) ( ( value_aligned >> byte_count ) & 0xffffffffUL );

        /* Change big-endian into little-endian

         */

        value_32bit = ( ( big_endian_value_32bit & 0x000000ffUL ) << 24 )

                    | ( ( big_endian_value_32bit & 0x0000ff00UL ) << 8 )

                    | ( ( big_endian_value_32bit >> 8 ) & 0x0000ff00UL )

                    | ( ( big_endian_value_32bit >> 24 ) & 0x000000ffUL );

      }

      else if( byte_order == _BYTE_STREAM_ENDIAN_LITTLE )

      {

        value_32bit = (uint32_t) value_aligned;

        value_aligned >>= byte_count;

      }

      byte_size -= 4;

      safe_checksum_value ^= value_32bit;

    }

    /* Re-align the buffer iterator

     */

    buffer_iterator = (uint8_t *) aligned_buffer_iterator;

    byte_size = 4 - ( alignment_size % 4 );

    if( byte_size != 4 )

    {

      value_32bit   = buffer_iterator[ 0 ];

      value_32bit <<= 8;

      if( byte_size >= 2 )

      {

        value_32bit |= buffer_iterator[ 1 ];

      }

      value_32bit <<= 8;

      if( byte_size >= 3 )

      {

        value_32bit |= buffer_iterator[ 2 ];

      }

      value_32bit <<= 8;

      buffer_iterator += byte_size;

      size            -= byte_size;

      safe_checksum_value ^= value_32bit;

    }

  }

  while( size > 0 )

  {

    value_32bit = 0;

    byte_count  = 1;

    if( size >= 4 )

    {

      value_32bit |= buffer_iterator[ 3 ];

      value_32bit <<= 8;

      byte_count++;

    }

    if( size >= 3 )

    {

      value_32bit |= buffer_iterator[ 2 ];

      value_32bit <<= 8;

      byte_count++;

    }

    if( size >= 2 )

    {

      value_32bit |= buffer_iterator[ 1 ];

      value_32bit <<= 8;

      byte_count++;

    }

    value_32bit |= buffer_iterator[ 0 ];

    buffer_iterator += byte_count;

    size            -= byte_count;

    safe_checksum_value ^= value_32bit;

  }

  *checksum_value = safe_checksum_value;

  return( 1 );

}