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67 lines
1.8 KiB
C
67 lines
1.8 KiB
C
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/*****************************
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* Copyright Henry Minsky (hqm@alum.mit.edu) 1991-2009
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*
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* This software library is licensed under terms of the GNU GENERAL
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* PUBLIC LICENSE
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*
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* RSCODE is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* RSCODE is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Rscode. If not, see <http://www.gnu.org/licenses/>.
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* Commercial licensing is available under a separate license, please
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* contact author for details.
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*
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* Source code is available at http://rscode.sourceforge.net
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*
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* CRC-CCITT generator simulator for byte wide data.
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*
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*
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* CRC-CCITT = x^16 + x^12 + x^5 + 1
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*
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*
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******************************/
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#include "ecc.h"
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BIT16 crchware(BIT16 data, BIT16 genpoly, BIT16 accum);
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/* Computes the CRC-CCITT checksum on array of byte data, length len
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*/
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BIT16 crc_ccitt(unsigned char *msg, int len)
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{
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int i;
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BIT16 acc = 0;
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for (i = 0; i < len; i++) {
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acc = crchware((BIT16) msg[i], (BIT16) 0x1021, acc);
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}
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return(acc);
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}
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/* models crc hardware (minor variation on polynomial division algorithm) */
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BIT16 crchware(BIT16 data, BIT16 genpoly, BIT16 accum)
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{
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static BIT16 i;
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data <<= 8;
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for (i = 8; i > 0; i--) {
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if ((data ^ accum) & 0x8000)
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accum = ((accum << 1) ^ genpoly) & 0xFFFF;
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else
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accum = (accum<<1) & 0xFFFF;
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data = (data<<1) & 0xFFFF;
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}
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return (accum);
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}
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