jamulus/src/audiocompr.cpp

/******************************************************************************\
 * Copyright (c) 2004-2006
 *
 * Author(s):
 *	Volker Fischer, Erik de Castro Lopo
 *
 * This code is based on the Open-Source implementation of IMA-ADPCM written
 * by Erik de Castro Lopo <erikd[at-#]mega-nerd[dot*]com> in 1999-2004
 *
 * Changes:
 * - only support for one channel
 * - put 2 audio samples in header to get even number of audio samples encoded
 *
 ******************************************************************************
 *
 * This program is free software; you can redistribute it and/or modify it under
 * the terms of the GNU General Public License as published by the Free Software
 * Foundation; either version 2 of the License, or (at your option) any later 
 * version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT 
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE. See the GNU General Public License for more 
 * details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc., 
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 *
\******************************************************************************/

#include "audiocompr.h"


/* Implementation *************************************************************/
int CAudioCompression::Init ( const int iNewAudioLen,
							  const EAudComprType eNewAuCoTy )
{
	eAudComprType = eNewAuCoTy;

	switch ( eNewAuCoTy )
	{
	case CT_NONE:
		return iCodeSize = 2 * iNewAudioLen; /* short = 2 * byte */

	case CT_IMAADPCM:
		return ImaAdpcm.Init ( iNewAudioLen );

	default: return 0;
	}
}

CVector<unsigned char> CAudioCompression::Encode ( const CVector<short>& vecsAudio )
{
	if (eAudComprType == CT_NONE)
	{
		/* no compression, simply ship pure samples */
		CVector<unsigned char> vecbyOut(iCodeSize);
		const int iAudSize = iCodeSize / 2;

		for (int i = 0; i < iAudSize; i++)
		{
			vecbyOut[2 * i] = vecsAudio[i] & 0xFF;
			vecbyOut[2 * i + 1] = (vecsAudio[i] >> 8) & 0xFF;
		}
		return vecbyOut;
	}
	else
	{
		switch ( eAudComprType )
		{
		case CT_IMAADPCM:
			return ImaAdpcm.Encode ( vecsAudio ); /* IMA-ADPCM */

		default:
			return CVector<unsigned char> ( 0 );
		}
	}
}

CVector<short> CAudioCompression::Decode(const CVector<unsigned char>& vecbyAdpcm)
{
	if (eAudComprType == CT_NONE)
	{
		/* no compression, reassemble pure samples */
		const int iAudSize = iCodeSize / 2;
		CVector<short> vecsOut(iAudSize);

		for (int i = 0; i < iAudSize; i++)
		{
			int current = vecbyAdpcm[2 * i] | (vecbyAdpcm[2 * i + 1] << 8);
			if (current & 0x8000)
				current -= 0x10000;

			vecsOut[i] = (short) current;
		}
		return vecsOut;
	}
	else
	{
		switch ( eAudComprType )
		{
		case CT_IMAADPCM:
			return ImaAdpcm.Decode ( vecbyAdpcm ); /* IMA-ADPCM */

		default:
			return CVector<short> ( 0 );
		}
	}
}


/* IMA-ADPCM implementation ------------------------------------------------- */
int CImaAdpcm::Init(const int iNewAudioLen)
{
	/* set lengths for audio and compressed data */
	iAudSize = iNewAudioLen;
	iAdpcmSize = 4 /* bytes header */ + (int) ceil(
		(double) (iAudSize - 2 /* first two samples are in header */) / 2);

	iStepindEnc = 0;

	return iAdpcmSize;
}

CVector<unsigned char> CImaAdpcm::Encode(const CVector<short>& vecsAudio)
{
	int						i;
	CVector<unsigned char>	vecbyAdpcm;
	CVector<unsigned char>	vecbyAdpcmTemp;

	/* init size */
	vecbyAdpcm.Init(iAdpcmSize);
	vecbyAdpcmTemp.Init(iAudSize);

	/* encode the block header ----------------------------------------------- */
	vecbyAdpcm[0] = vecsAudio[0] & 0xFF;
	vecbyAdpcm[1] = (vecsAudio[0] >> 8) & 0xFF;
	vecbyAdpcm[2] = iStepindEnc;

	int iPrevAudio = vecsAudio[0];


	/* encode the samples as 4 bit ------------------------------------------- */
	for (i = 1; i < iAudSize; i++)
	{
		/* init diff and step */
		int diff = vecsAudio[i] - iPrevAudio;
		int step = ima_step_size[iStepindEnc];

		short bytecode = 0;

		int vpdiff = step >> 3;
		if (diff < 0)
		{
			bytecode = 8;
			diff = -diff;
		}
		short mask = 4;
		while (mask)
		{
			if (diff >= step)
			{
				bytecode |= mask;
				diff -= step;
				vpdiff += step;
			}
			step >>= 1;
			mask >>= 1;
		}

		if (bytecode & 8)
			iPrevAudio -= vpdiff;
		else
			iPrevAudio += vpdiff;

		/* adjust step size */
		iStepindEnc += ima_indx_adjust[bytecode];

		/* check that values do not exceed the bounds */
		iPrevAudio = CheckBounds(iPrevAudio, _MINSHORT, _MAXSHORT);
		iStepindEnc = CheckBounds(iStepindEnc, 0, IMA_STEP_SIZE_TAB_LEN - 1);

		/* use the input buffer as an intermediate result buffer */
		vecbyAdpcmTemp[i] = bytecode;
	}


	/* pack the 4 bit encoded samples ---------------------------------------- */
	/* The first encoded audio sample is in header */
	vecbyAdpcm[3] = vecbyAdpcmTemp[1] & 0x0F;

	for (i = 4; i < iAdpcmSize; i++)
	{
		vecbyAdpcm[i] = vecbyAdpcmTemp[2 * i - 6] & 0x0F;
		vecbyAdpcm[i] |= (vecbyAdpcmTemp[2 * i - 5] << 4) & 0xF0;
	}

	return vecbyAdpcm;
}

CVector<short> CImaAdpcm::Decode(const CVector<unsigned char>& vecbyAdpcm)
{
	int				i;
	CVector<short>	vecsAudio;

	vecsAudio.Init(iAudSize);


	/* read and check the block header --------------------------------------- */
	int current = vecbyAdpcm[0] | (vecbyAdpcm[1] << 8);
	if (current & 0x8000)
		current -= 0x10000;

	/* get and bound step index */
	int iStepindDec = CheckBounds(vecbyAdpcm[2], 0, IMA_STEP_SIZE_TAB_LEN - 1);

	/* set first sample which was delivered in the header */
	vecsAudio[0] = current;


	/* --------------------------------------------------------------------------
	   pull apart the packed 4 bit samples and store them in their correct sample
	   positions */
	/* The first encoded audio sample is in header */
	vecsAudio[1] = vecbyAdpcm[3] & 0x0F;

	for (i = 4; i < iAdpcmSize; i++)
	{
		const short bytecode = vecbyAdpcm[i];
		vecsAudio[2 * i - 6] = bytecode & 0x0F;
		vecsAudio[2 * i - 5] = (bytecode >> 4) & 0x0F;
	}


	/* decode the encoded 4 bit samples -------------------------------------- */
	for (i = 1; i < iAudSize; i++)
	{
		const short bytecode = vecsAudio[i] & 0xF ;

		short step = ima_step_size[iStepindDec];
		int current = vecsAudio[i - 1];

		int diff = step >> 3;
		if (bytecode & 1)
			diff += step >> 2;
		if (bytecode & 2)
			diff += step >> 1;
		if (bytecode & 4)
			diff += step;
		if (bytecode & 8)
			diff = -diff;

		current += diff;
		iStepindDec += ima_indx_adjust[bytecode];

		/* check that values do not exceed the bounds */
		current = CheckBounds(current, _MINSHORT, _MAXSHORT);
		iStepindDec = CheckBounds(iStepindDec, 0, IMA_STEP_SIZE_TAB_LEN - 1);

		vecsAudio[i] = current;
	}

	return vecsAudio;
}