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Annotation of multiplexer/crc16.c, revision 1.1

1.1     ! oskar       1: /*
        !             2:  * cyclic redundancy check 16 bit
        !             3:  * Copyright (C) 1999 Christian Wolff, 2004 Oskar Schirmer
        !             4:  * for Convergence Integrated Media GmbH (http://www.convergence.de)
        !             5:  *
        !             6:  * This program is free software; you can redistribute it and/or modify
        !             7:  * it under the terms of the GNU General Public License as published by
        !             8:  * the Free Software Foundation; either version 2 of the License, or
        !             9:  * (at your option) any later version.
        !            10:  *
        !            11:  * This program is distributed in the hope that it will be useful,
        !            12:  * but WITHOUT ANY WARRANTY; without even the implied warranty of
        !            13:  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
        !            14:  * GNU 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
        !            19:  */
        !            20: 
        !            21: #include <sys/types.h>
        !            22: #include "crc16.h"
        !            23: 
        !            24: u_int16_t crc_16_table[256];
        !            25: 
        !            26: // generate the tables of CRC-16 remainders for all possible bytes
        !            27: void gen_crc16_table() { 
        !            28:   register int i,j;  
        !            29:   register u_int16_t crc16;
        !            30:   for (i=0; i<256; i++) {
        !            31:     crc16=(u_int16_t)i << 8;
        !            32:     for (j=0; j<8; j++) {
        !            33:       crc16 = (crc16 << 1) ^ ((crc16 & (1<<15)) ? POLYNOMIAL_16_MSBF : 0);
        !            34:     }
        !            35:     crc_16_table[i]=crc16; 
        !            36:   }
        !            37: }
        !            38: 
        !            39: // update the CRC on the data block one byte at a time
        !            40: u_int16_t update_crc_16_block(u_int16_t crc, char *data_block_ptr, int data_block_size)
        !            41: {
        !            42:   register int i;
        !            43:   for (i=data_block_size; i>0; i--)
        !            44:     crc=update_crc_16(crc, *data_block_ptr++);
        !            45:   return crc;
        !            46: }
        !            47: 
        !            48: void crc16_calc (char *data,
        !            49:     int size,
        !            50:     char *crc)
        !            51: {
        !            52:   u_int16_t c;
        !            53:   c = CRC_INIT_16;
        !            54:   while (--size >= 0) {
        !            55:     c = update_crc_16 (c,*data++);
        !            56:   }
        !            57:   crc[1] = c; c >>= 8;
        !            58:   crc[0] = c;
        !            59: }
        !            60: