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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. /** IP checksum value for computed zero checksum.
  46.  *  Zero is returned as 0xFFFF (not flipped)
  47.  */
  48. #define IP_CHECKSUM_ZERO            0xFFFFu
  49.  
  50. uint32_t compute_crc32_le( uint32_t seed, uint8_t * data, size_t length ){
  51.     size_t  index;
  52.  
  53.     while( length >= 8 ){
  54.         seed ^= ( * data );
  55.         for( index = 0; index < 8; ++ index ){
  56.             if( seed & 1 ){
  57.                 seed = ( seed >> 1 ) ^ (( uint32_t ) CRC_DIVIDER_LE );
  58.             }else{
  59.                 seed >>= 1;
  60.             }
  61.         }
  62.         ++ data;
  63.         length -= 8;
  64.     }
  65.     if( length > 0 ){
  66.         seed ^= ( * data ) >> ( 8 - length );
  67.         for( index = 0; index < length; ++ index ){
  68.             if( seed & 1 ){
  69.                 seed = ( seed >> 1 ) ^ (( uint32_t ) CRC_DIVIDER_LE );
  70.             }else{
  71.                 seed >>= 1;
  72.             }
  73.         }
  74.         length -= 8;
  75.     }
  76.     return seed;
  77. }
  78.  
  79. uint32_t compute_crc32_be( uint32_t seed, uint8_t * data, size_t length ){
  80.     size_t  index;
  81.  
  82.     while( length >= 8 ){
  83.         seed ^= ( * data ) << 24;
  84.         for( index = 0; index < 8; ++ index ){
  85.             if( seed & 0x80000000 ){
  86.                 seed = ( seed << 1 ) ^ (( uint32_t ) CRC_DIVIDER_BE );
  87.             }else{
  88.                 seed <<= 1;
  89.             }
  90.         }
  91.         ++ data;
  92.         length -= 8;
  93.     }
  94.     if( length > 0 ){
  95.         seed ^= (( * data ) & ( 0xFF << ( 8 - length ))) << 24;
  96.         for( index = 0; index < length; ++ index ){
  97.             if( seed & 0x80000000 ){
  98.                 seed = ( seed << 1 ) ^ (( uint32_t ) CRC_DIVIDER_BE );
  99.             }else{
  100.                 seed <<= 1;
  101.             }
  102.         }
  103.         length -= 8;
  104.     }
  105.     return seed;
  106. }
  107.  
  108. uint32_t compute_checksum( uint32_t seed, uint8_t * data, size_t length ){
  109.     size_t  index;
  110.  
  111.     // sum all the 16 bit fields
  112.     for( index = 0; index + 1 < length; index += 2 ){
  113.         seed += ( data[ index ] << 8 ) + data[ index + 1 ];
  114.     }
  115.  
  116.     // last odd byte with zero padding
  117.     if( index + 1 == length ){
  118.         seed += data[ index ] << 8;
  119.     }
  120.  
  121.     return seed;
  122. }
  123.  
  124. uint16_t compact_checksum( uint32_t sum ){
  125.     // shorten to the 16 bits
  126.     while( sum >> 16 ) sum = ( sum & 0xFFFF ) + ( sum >> 16 );
  127.  
  128.     return ( uint16_t ) sum;
  129. }
  130.  
  131. uint16_t flip_checksum( uint16_t checksum ){
  132.     // flip, zero is returned as 0xFFFF (not flipped)
  133.     return ( ~ checksum ) ? ( uint16_t ) ( ~ checksum ) : IP_CHECKSUM_ZERO;
  134. }
  135.  
  136. uint16_t ip_checksum( uint8_t * data, size_t length ){
  137.     return flip_checksum( compact_checksum( compute_checksum( 0, data, length )));
  138. }
  139.  
  140. /** @}
  141.  */
  142.