src/crypto/crc32.c

   1 /*
   2  * Little-endian CRC32 implementation.
   3  *
   4  * Copyright (c) 2009 Joshua Oreman <oremanj@rwcr.net>.
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public License as
   8  * published by the Free Software Foundation; either version 2 of the
   9  * License, or any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful, but
  12  * WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  * General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program; if not, write to the Free Software
  18  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  19  */
  20
  21 FILE_LICENCE ( GPL2_OR_LATER );
  22
  23 #include <gpxe/crc32.h>
  24
  25 #define CRCPOLY         0xedb88320
  26
  27 /**
  28  * Calculate 32-bit little-endian CRC checksum
  29  *
  30  * @v seed      Initial value
  31  * @v data      Data to checksum
  32  * @v len       Length of data
  33  *
  34  * Usually @a seed is initially zero or all one bits, depending on the
  35  * protocol. To continue a CRC checksum over multiple calls, pass the
  36  * return value from one call as the @a seed parameter to the next.
  37  */
  38 u32 crc32_le ( u32 seed, const void *data, size_t len )
  39 {
  40         u32 crc = seed;
  41         const u8 *src = data;
  42         u32 mult;
  43         int i;
  44
  45         while ( len-- ) {
  46                 crc ^= *src++;
  47                 for ( i = 0; i < 8; i++ ) {
  48                         mult = ( crc & 1 ) ? CRCPOLY : 0;
  49                         crc = ( crc >> 1 ) ^ mult;
  50                 }
  51         }
  52
  53         return crc;
  54 }