mulawencoder.cpp

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#include "mulawencoder.h"

/*
 * Based on example code from http://hazelware.luggle.com/tutorials/mulawcompression.html
 */

static const TInt KMuLawBias = 0x84;
static const TInt KMuLawClip = 32635;

static const TUint8 KMuLawCompressTable[] = {
	 0, 0, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3,
	 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
	 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
	 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
	 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
	 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
	 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
	 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
	 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
	 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
	 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
	 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
	 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
	 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
	 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
	 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7
};

static TUint8 ToMuLaw(TInt16 aSample) {
	TInt sign = (aSample >> 8) & 0x80;
	if (sign)
		aSample = (TInt16) -(aSample + 1); // the +1 is for handling the case when aSample == -32768
	if (aSample > KMuLawClip)
		aSample = KMuLawClip;
	aSample += KMuLawBias;
	TInt exponent = KMuLawCompressTable[(aSample >> 7) & 0xFF];
	TInt mantissa = (aSample >> (exponent + 3)) & 0x0F;
	TUint8 compressedByte = ~ (sign | (exponent << 4) | mantissa);

	return compressedByte;
}

TInt CMuLawEncoder::Encode(const TDesC8& aBuffer, TUint8* aOutBuffer) {
	const TInt16* ptr = reinterpret_cast<const TInt16*>(aBuffer.Ptr());
	TInt len = aBuffer.Length()/2;
	for (TInt i = 0; i < len; i++) {
		*aOutBuffer = ToMuLaw(*ptr);
		ptr++;
		aOutBuffer++;
	}
	return len;
}