AUDIO: Cleanup MS IMA handling

- Split The Last Express' ADPCM to the engine. Using the MS IMA routine was really a hack.
- Fixed stereo MS IMA ADPCM, the old routine was completely wrong.

4 files changed, 82 insertions, 57 deletions

diff --git a/audio/decoders/adpcm.cpp b/audio/decoders/adpcm.cpp
index ac18b244c5..3b53ca2fd1 100644
--- a/audio/decoders/adpcm.cpp
+++ b/audio/decoders/adpcm.cpp
@@ -201,60 +201,49 @@ int Apple_ADPCMStream::readBuffer(int16 *buffer, const int numSamples) {
 	return samples[0] + samples[1];
 }
 
+
 #pragma mark -
 
 
-int MSIma_ADPCMStream::readBufferMSIMA1(int16 *buffer, const int numSamples) {
-	int samples = 0;
-	byte data;
+int MSIma_ADPCMStream::readBuffer(int16 *buffer, const int numSamples) {
+	// Need to write at least one sample per channel
+	assert((numSamples % _channels) == 0);
 
-	assert(numSamples % 2 == 0);
+	int samples = 0;
 
 	while (samples < numSamples && !_stream->eos() && _stream->pos() < _endpos) {
 		if (_blockPos[0] == _blockAlign) {
-			// read block header
-			_status.ima_ch[0].last = _stream->readSint16LE();
-			_status.ima_ch[0].stepIndex = _stream->readSint16LE();
-			_blockPos[0] = 4;
-		}
+			for (int i = 0; i < _channels; i++) {
+				// read block header
+				_status.ima_ch[i].last = _stream->readSint16LE();
+				_status.ima_ch[i].stepIndex = _stream->readSint16LE();
+			}
 
-		for (; samples < numSamples && _blockPos[0] < _blockAlign && !_stream->eos() && _stream->pos() < _endpos; samples += 2) {
-			data = _stream->readByte();
-			_blockPos[0]++;
-			buffer[samples] = decodeIMA(_invertSamples ? (data >> 4) & 0x0f : data & 0x0f);
-			buffer[samples + 1] = decodeIMA(_invertSamples ? data & 0x0f : (data >> 4) & 0x0f);
+			_blockPos[0] = _channels * 4;
 		}
-	}
-	return samples;
-}
 
+		// Decode a set of samples
+		for (int i = 0; i < _channels; i++) {
+			// The stream encodes four bytes per channel at a time
+			for (int j = 0; j < 4; j++) {
+				byte data = _stream->readByte();
+				_blockPos[0]++;
+				_buffer[i][j * 2] = decodeIMA(data & 0x0f, i);
+				_buffer[i][j * 2 + 1] = decodeIMA((data >> 4) & 0x0f, i);
+				_samplesLeft[i] += 2;
+			}
+		}
 
-// Microsoft as usual tries to implement it differently. This method
-// is used for stereo data.
-int MSIma_ADPCMStream::readBufferMSIMA2(int16 *buffer, const int numSamples) {
-	int samples;
-	uint32 data;
-	int nibble;
-	byte k;
-
-	// TODO: Currently this implementation only supports
-	// reading a multiple of 16 samples at once. We might
-	// consider changing that so it could read an arbitrary
-	// sample pair count.
-	assert(numSamples % 16 == 0);
-
-	for (samples = 0; samples < numSamples && !_stream->eos() && _stream->pos() < _endpos;) {
-		for (int channel = 0; channel < 2; channel++) {
-			data = _stream->readUint32LE();
-
-			for (nibble = 0; nibble < 8; nibble++) {
-				k = ((data & 0xf0000000) >> 28);
-				buffer[samples + channel + nibble * 2] = decodeIMA(k);
-				data <<= 4;
+		while (samples < numSamples && _samplesLeft[0] != 0) {
+			for (int i = 0; i < _channels; i++) {
+				buffer[samples] = _buffer[i][8 - _samplesLeft[i]];
+				_samplesLeft[i]--;
 			}
+
+			samples += _channels;
 		}
-		samples += 16;
 	}
+
 	return samples;
 }
 
@@ -449,8 +438,6 @@ RewindableAudioStream *makeADPCMStream(Common::SeekableReadStream *stream, Dispo
 		return new Oki_ADPCMStream(stream, disposeAfterUse, size, rate, channels, blockAlign);
 	case kADPCMMSIma:
 		return new MSIma_ADPCMStream(stream, disposeAfterUse, size, rate, channels, blockAlign);
-	case kADPCMMSImaLastExpress:
-		return new MSIma_ADPCMStream(stream, disposeAfterUse, size, rate, channels, blockAlign, true);
 	case kADPCMMS:
 		return new MS_ADPCMStream(stream, disposeAfterUse, size, rate, channels, blockAlign);
 	case kADPCMDVI:
diff --git a/audio/decoders/adpcm.h b/audio/decoders/adpcm.h
index 7202d6bc9c..f6b424c463 100644
--- a/audio/decoders/adpcm.h
+++ b/audio/decoders/adpcm.h
@@ -56,7 +56,6 @@ class RewindableAudioStream;
 enum typesADPCM {
 	kADPCMOki,                 // Dialogic/Oki ADPCM (aka VOX)
 	kADPCMMSIma,               // Microsoft IMA ADPCM
-	kADPCMMSImaLastExpress,    // Microsoft IMA ADPCM (with inverted samples)
 	kADPCMMS,                  // Microsoft ADPCM
 	kADPCMDVI,                 // Intel DVI IMA ADPCM
 	kADPCMApple,               // Apple QuickTime IMA ADPCM
diff --git a/audio/decoders/adpcm_intern.h b/audio/decoders/adpcm_intern.h
index ea20b40338..dd8c14be79 100644
--- a/audio/decoders/adpcm_intern.h
+++ b/audio/decoders/adpcm_intern.h
@@ -148,24 +148,30 @@ public:
 
 class MSIma_ADPCMStream : public Ima_ADPCMStream {
 public:
-	MSIma_ADPCMStream(Common::SeekableReadStream *stream, DisposeAfterUse::Flag disposeAfterUse, uint32 size, int rate, int channels, uint32 blockAlign, bool invertSamples = false)
-		: Ima_ADPCMStream(stream, disposeAfterUse, size, rate, channels, blockAlign), _invertSamples(invertSamples) {
+	MSIma_ADPCMStream(Common::SeekableReadStream *stream, DisposeAfterUse::Flag disposeAfterUse, uint32 size, int rate, int channels, uint32 blockAlign)
+		: Ima_ADPCMStream(stream, disposeAfterUse, size, rate, channels, blockAlign) {
+
 		if (blockAlign == 0)
-			error("ADPCMStream(): blockAlign isn't specified for MS IMA ADPCM");
-	}
+			error("MSIma_ADPCMStream(): blockAlign isn't specified");
 
-	virtual int readBuffer(int16 *buffer, const int numSamples) {
-		if (_channels == 1)
-			return readBufferMSIMA1(buffer, numSamples);
-		else
-			return readBufferMSIMA2(buffer, numSamples);
+		if (blockAlign % (_channels * 4))
+			error("MSIma_ADPCMStream(): invalid blockAlign");
+
+		_samplesLeft[0] = 0;
+		_samplesLeft[1] = 0;
 	}
 
-	int readBufferMSIMA1(int16 *buffer, const int numSamples);
-	int readBufferMSIMA2(int16 *buffer, const int numSamples);
+	virtual int readBuffer(int16 *buffer, const int numSamples);
+
+	void reset() {
+		Ima_ADPCMStream::reset();
+		_samplesLeft[0] = 0;
+		_samplesLeft[1] = 0;
+	}
 
 private:
-	bool _invertSamples;    // Some implementations invert the way samples are decoded
+	int16 _buffer[2][8];
+	int _samplesLeft[2];
 };
 
 class MS_ADPCMStream : public ADPCMStream {
diff --git a/engines/lastexpress/data/snd.cpp b/engines/lastexpress/data/snd.cpp
index bd2320726a..6389489abb 100644
--- a/engines/lastexpress/data/snd.cpp
+++ b/engines/lastexpress/data/snd.cpp
@@ -30,12 +30,45 @@
 
 #include "lastexpress/debug.h"
 
-#include "audio/decoders/adpcm.h"
+#include "audio/decoders/adpcm_intern.h"
 #include "audio/audiostream.h"
 #include "common/memstream.h"
 
 namespace LastExpress {
 
+// Last Express ADPCM is similar to MS IMA mono, but inverts its nibbles
+// and does not have the 4 byte per channel requirement
+
+class LastExpress_ADPCMStream : public Audio::Ima_ADPCMStream {
+public:
+	LastExpress_ADPCMStream(Common::SeekableReadStream *stream, DisposeAfterUse::Flag disposeAfterUse, uint32 size, uint32 blockSize) :
+			Audio::Ima_ADPCMStream(stream, disposeAfterUse, size, 44100, 1, blockSize) {}
+
+	int readBuffer(int16 *buffer, const int numSamples) {
+		int samples = 0;
+
+		assert(numSamples % 2 == 0);
+
+		while (samples < numSamples && !_stream->eos() && _stream->pos() < _endpos) {
+			if (_blockPos[0] == _blockAlign) {
+				// read block header
+				_status.ima_ch[0].last = _stream->readSint16LE();
+				_status.ima_ch[0].stepIndex = _stream->readSint16LE();
+				_blockPos[0] = 4;
+			}
+
+			for (; samples < numSamples && _blockPos[0] < _blockAlign && !_stream->eos() && _stream->pos() < _endpos; samples += 2) {
+				byte data = _stream->readByte();
+				_blockPos[0]++;
+				buffer[samples] = decodeIMA((data >> 4) & 0x0f);
+				buffer[samples + 1] = decodeIMA(data & 0x0f);
+			}
+		}
+
+		return samples;
+	}
+};
+
 //////////////////////////////////////////////////////////////////////////
 // Sound
 //////////////////////////////////////////////////////////////////////////
@@ -60,7 +93,7 @@ void SimpleSound::loadHeader(Common::SeekableReadStream *in) {
 }
 
 Audio::AudioStream *SimpleSound::makeDecoder(Common::SeekableReadStream *in, uint32 size) const {
-	return Audio::makeADPCMStream(in, DisposeAfterUse::YES, size, Audio::kADPCMMSImaLastExpress, 44100, 1, _blockSize);
+	return new LastExpress_ADPCMStream(in, DisposeAfterUse::YES, size, _blockSize);
 }
 
 void SimpleSound::play(Audio::AudioStream *as) {