mirror of
https://github.com/cookiengineer/audacity
synced 2025-10-31 22:23:54 +01:00
85 lines
2.2 KiB
C
85 lines
2.2 KiB
C
/*
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* TwoLAME: an optimized MPEG Audio Layer Two encoder
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*
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* Copyright (C) 2001-2004 Michael Cheng
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* Copyright (C) 2004-2006 The TwoLAME Project
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* This library 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 GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*
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* $Id$
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*
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*/
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#include <stdio.h>
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#include <string.h>
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#include "twolame.h"
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#include "common.h"
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#include "bitbuffer.h"
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#include "encode.h"
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#include "crc.h"
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static unsigned int crc_update(unsigned int value, unsigned int crc, unsigned int nbBit)
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{
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int i;
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value <<= 8;
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for (i = 0; i < nbBit; i++) {
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value <<= 1;
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crc <<= 1;
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if (((crc ^ value) & 0x10000))
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crc ^= CRC16_POLYNOMIAL;
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}
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return crc;
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}
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/*
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* The CRC is based on the second two bytes of the MPEG audio header
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* and then the bits up and until the scale-factor bits.
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*/
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void crc_writeheader(unsigned char *bitstream, int bit_count)
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{
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unsigned int crc = 0xffff; /* (jo) init crc16 for error_protection */
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int whole_bytes = (bit_count >> 3);
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int byte;
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// Calculate the CRC on the second two bytes of the header
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crc = crc_update(bitstream[2], crc, 8);
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crc = crc_update(bitstream[3], crc, 8);
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// Calculate CRC on whole bytes after CRC
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for (byte = 6; byte < (whole_bytes + 6); byte++) {
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crc = crc_update(bitstream[byte], crc, 8);
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}
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// Calculate CRC on remaining bits
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if (bit_count & 7) {
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crc = crc_update(bitstream[byte], crc, bit_count & 7);
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}
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// Insert the CRC into the 16-bits after the header
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bitstream[4] = crc >> 8;
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bitstream[5] = crc & 0xFF;
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}
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// vim:ts=4:sw=4:nowrap:
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