/*

 * Checksum functions

 *

 * Copyright (C) 2011-2024, 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 <types.h>

#include "libfvde_libcerror.h"

/* Table of CRC-32 values of 8-bit values

 */

uint32_t libfvde_checksum_crc32_table[ 256 ];

/* Value to indicate the CRC-32 table been computed

 */

int libfvde_checksum_crc32_table_computed = 0;

/* Initializes the internal CRC-32 table

 * The table speeds up the CRC-32 calculation

 */

void libfvde_checksum_initialize_crc32_table(

      uint32_t polynomial )

{

  uint32_t checksum    = 0;

  uint32_t table_index = 0;

  uint8_t bit_iterator = 0;

  for( table_index = 0;

       table_index < 256;

       table_index++ )

  {

    checksum = (uint32_t) table_index;

    for( bit_iterator = 0;

         bit_iterator < 8;

         bit_iterator++ )

    {

      if( checksum & 1 )

      {

        checksum = polynomial ^ ( checksum >> 1 );

      }

      else

      {

        checksum = checksum >> 1;

      }

    }

    libfvde_checksum_crc32_table[ table_index ] = checksum;

  }

  libfvde_checksum_crc32_table_computed = 1;

}

/* Calculates the weak CRC-32 checksum of a buffer

 * Returns 1 if successful or -1 on error

 */

int libfvde_checksum_calculate_weak_crc32(

     uint32_t *checksum,

     const uint8_t *buffer,

     size_t size,

     uint32_t initial_value,

     libcerror_error_t **error )

{

  static char *function = "libfvde_checkcum_calculate_weak_crc32";

  size_t buffer_offset  = 0;

  uint32_t table_index  = 0;

  if( checksum == NULL )

  {

    libcerror_error_set(

     error,

     LIBCERROR_ERROR_DOMAIN_ARGUMENTS,

     LIBCERROR_ARGUMENT_ERROR_INVALID_VALUE,

     "%s: invalid checksum.",

     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 );

  }

        if( libfvde_checksum_crc32_table_computed == 0 )

  {

    libfvde_checksum_initialize_crc32_table(

     0x82f63b78UL );

  }

  *checksum = initial_value;

        for( buffer_offset = 0;

       buffer_offset < size;

       buffer_offset++ )

  {

    table_index = ( *checksum ^ buffer[ buffer_offset ] ) & 0x000000ffUL;

    *checksum = libfvde_checksum_crc32_table[ table_index ] ^ ( *checksum >> 8 );

        }

  return( 1 );

}