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  1. /*
  2.  * Copyright (c) 2009 Lukas Mejdrech
  3.  * All rights reserved.
  4.  *
  5.  * Redistribution and use in source and binary forms, with or without
  6.  * modification, are permitted provided that the following conditions
  7.  * are met:
  8.  *
  9.  * - Redistributions of source code must retain the above copyright
  10.  *   notice, this list of conditions and the following disclaimer.
  11.  * - Redistributions in binary form must reproduce the above copyright
  12.  *   notice, this list of conditions and the following disclaimer in the
  13.  *   documentation and/or other materials provided with the distribution.
  14.  * - The name of the author may not be used to endorse or promote products
  15.  *   derived from this software without specific prior written permission.
  16.  *
  17.  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  18.  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  19.  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  20.  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  21.  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  22.  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23.  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24.  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25.  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  26.  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27.  */
  28.  
  29. /** @addtogroup net
  30.  *  @{
  31.  */
  32.  
  33. /** @file
  34.  *  General CRC and checksum computation implementation.
  35.  */
  36.  
  37. #include <sys/types.h>
  38.  
  39. #include "include/crc.h"
  40.  
  41. #define CRC_DIVIDER_BE  0x04C11DB7
  42.  
  43. #define CRC_DIVIDER_LE  0xEDB88320
  44.  
  45. uint32_t compute_crc32_le( uint32_t seed, uint8_t * data, size_t length ){
  46.     size_t  index;
  47.  
  48.     while( length >= 8 ){
  49.         seed ^= ( * data );
  50.         for( index = 0; index < 8; ++ index ){
  51.             if( seed & 1 ){
  52.                 seed = ( seed >> 1 ) ^ (( uint32_t ) CRC_DIVIDER_LE );
  53.             }else{
  54.                 seed >>= 1;
  55.             }
  56.         }
  57.         ++ data;
  58.         length -= 8;
  59.     }
  60.     if( length > 0 ){
  61.         seed ^= ( * data ) >> ( 8 - length );
  62.         for( index = 0; index < length; ++ index ){
  63.             if( seed & 1 ){
  64.                 seed = ( seed >> 1 ) ^ (( uint32_t ) CRC_DIVIDER_LE );
  65.             }else{
  66.                 seed >>= 1;
  67.             }
  68.         }
  69.         length -= 8;
  70.     }
  71.     return seed;
  72. }
  73.  
  74. uint32_t compute_crc32_be( uint32_t seed, uint8_t * data, size_t length ){
  75.     size_t  index;
  76.  
  77.     while( length >= 8 ){
  78.         seed ^= ( * data ) << 24;
  79.         for( index = 0; index < 8; ++ index ){
  80.             if( seed & 0x80000000 ){
  81.                 seed = ( seed << 1 ) ^ (( uint32_t ) CRC_DIVIDER_BE );
  82.             }else{
  83.                 seed <<= 1;
  84.             }
  85.         }
  86.         ++ data;
  87.         length -= 8;
  88.     }
  89.     if( length > 0 ){
  90.         seed ^= (( * data ) & ( 0xFF << ( 8 - length ))) << 24;
  91.         for( index = 0; index < length; ++ index ){
  92.             if( seed & 0x80000000 ){
  93.                 seed = ( seed << 1 ) ^ (( uint32_t ) CRC_DIVIDER_BE );
  94.             }else{
  95.                 seed <<= 1;
  96.             }
  97.         }
  98.         length -= 8;
  99.     }
  100.     return seed;
  101. }
  102.  
  103. uint32_t compute_checksum( uint32_t seed, uint8_t * data, size_t length ){
  104.     size_t  index;
  105.  
  106.     // sum all the 16 bit fields
  107.     for( index = 0; index + 1 < length; index += 2 ){
  108.         seed += ( data[ index ] << 8 ) + data[ index + 1 ];
  109.     }
  110.  
  111.     // last odd byte with zero padding
  112.     if( index + 1 == length ){
  113.         seed += data[ index ] << 8;
  114.     }
  115.  
  116.     return seed;
  117. }
  118.  
  119. uint16_t compact_checksum( uint32_t sum ){
  120.     // shorten to the 16 bits
  121.     while( sum >> 16 ) sum = ( sum & 0xFFFF ) + ( sum >> 16 );
  122.  
  123.     return ( uint16_t ) sum;
  124. }
  125.  
  126. /** @}
  127.  */
  128.