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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/checksum.h"
  40.  
  41. /** Big-endian encoding CRC divider.
  42.  */
  43. #define CRC_DIVIDER_BE  0x04C11DB7
  44.  
  45. /** Little-endian encoding CRC divider.
  46.  */
  47. #define CRC_DIVIDER_LE  0xEDB88320
  48.  
  49. /** IP checksum value for computed zero checksum.
  50.  *  Zero is returned as 0xFFFF (not flipped)
  51.  */
  52. #define IP_CHECKSUM_ZERO            0xFFFFu
  53.  
  54. uint32_t compute_crc32_le( uint32_t seed, uint8_t * data, size_t length ){
  55.     size_t  index;
  56.  
  57.     while( length >= 8 ){
  58.         seed ^= ( * data );
  59.         for( index = 0; index < 8; ++ index ){
  60.             if( seed & 1 ){
  61.                 seed = ( seed >> 1 ) ^ (( uint32_t ) CRC_DIVIDER_LE );
  62.             }else{
  63.                 seed >>= 1;
  64.             }
  65.         }
  66.         ++ data;
  67.         length -= 8;
  68.     }
  69.     if( length > 0 ){
  70.         seed ^= ( * data ) >> ( 8 - length );
  71.         for( index = 0; index < length; ++ index ){
  72.             if( seed & 1 ){
  73.                 seed = ( seed >> 1 ) ^ (( uint32_t ) CRC_DIVIDER_LE );
  74.             }else{
  75.                 seed >>= 1;
  76.             }
  77.         }
  78.         length -= 8;
  79.     }
  80.     return seed;
  81. }
  82.  
  83. uint32_t compute_crc32_be( uint32_t seed, uint8_t * data, size_t length ){
  84.     size_t  index;
  85.  
  86.     while( length >= 8 ){
  87.         seed ^= ( * data ) << 24;
  88.         for( index = 0; index < 8; ++ index ){
  89.             if( seed & 0x80000000 ){
  90.                 seed = ( seed << 1 ) ^ (( uint32_t ) CRC_DIVIDER_BE );
  91.             }else{
  92.                 seed <<= 1;
  93.             }
  94.         }
  95.         ++ data;
  96.         length -= 8;
  97.     }
  98.     if( length > 0 ){
  99.         seed ^= (( * data ) & ( 0xFF << ( 8 - length ))) << 24;
  100.         for( index = 0; index < length; ++ index ){
  101.             if( seed & 0x80000000 ){
  102.                 seed = ( seed << 1 ) ^ (( uint32_t ) CRC_DIVIDER_BE );
  103.             }else{
  104.                 seed <<= 1;
  105.             }
  106.         }
  107.         length -= 8;
  108.     }
  109.     return seed;
  110. }
  111.  
  112. uint32_t compute_checksum( uint32_t seed, uint8_t * data, size_t length ){
  113.     size_t  index;
  114.  
  115.     // sum all the 16 bit fields
  116.     for( index = 0; index + 1 < length; index += 2 ){
  117.         seed += ( data[ index ] << 8 ) + data[ index + 1 ];
  118.     }
  119.  
  120.     // last odd byte with zero padding
  121.     if( index + 1 == length ){
  122.         seed += data[ index ] << 8;
  123.     }
  124.  
  125.     return seed;
  126. }
  127.  
  128. uint16_t compact_checksum( uint32_t sum ){
  129.     // shorten to the 16 bits
  130.     while( sum >> 16 ) sum = ( sum & 0xFFFF ) + ( sum >> 16 );
  131.  
  132.     return ( uint16_t ) sum;
  133. }
  134.  
  135. uint16_t flip_checksum( uint16_t checksum ){
  136.     // flip, zero is returned as 0xFFFF (not flipped)
  137.     return ( ~ checksum ) ? ( uint16_t ) ( ~ checksum ) : IP_CHECKSUM_ZERO;
  138. }
  139.  
  140. uint16_t ip_checksum( uint8_t * data, size_t length ){
  141.     return flip_checksum( compact_checksum( compute_checksum( 0, data, length )));
  142. }
  143.  
  144. /** @}
  145.  */
  146.