ImaAdpcmDecoder: Rework sample decode/predict, and finalize funcs

With this, the decodeSample() method should now be a pretty close
match to cs.columbia's doc, also, since functions here won't be
overriden or changed in any way during execution, mark them as
final too. This commit also fixes an oversight where both
inputIndex and outputIndex were converted to byte, whereas they
should have been kept as int or else longer streams would overflow.

src/org/recompile/mobile/WavImaAdpcmDecoder.java

@@ -67,11 +67,11 @@ public class WavImaAdpcmDecoder
 	/* 
 	 * This method will decode IMA WAV ADPCM into linear PCM_S16LE.
 	 */
-	public static byte[] decodeADPCM(final byte[] input, int inputSize, final short numChannels, final int frameSize)
+	public static final byte[] decodeADPCM(final byte[] input, int inputSize, final short numChannels, final int frameSize)
 	{
 		byte adpcmSample;
 		byte curChannel;
-		byte inputIndex = 0, outputIndex = HEADERSIZE; /* Give some space for the header by starting from byte 44. */
+		int inputIndex = 0, outputIndex = HEADERSIZE; /* Give some space for the header by starting from byte 44. */
 		int decodedSample;
 
 		/* 
@@ -197,27 +197,30 @@ public static byte[] decodeADPCM(final byte[] input, int inputSize, final short
 	}
 
 	/* This method will decode a single IMA ADPCM sample to linear PCM_S16LE sample. */
-	static short decodeSample(final byte channel, byte adpcmSample)
+	private static final short decodeSample(final byte channel, final byte adpcmSample)
 	{
 		/* 
 		 * This decode procedure is based on the following document:
 		 * https://www.cs.columbia.edu/~hgs/audio/dvi/IMA_ADPCM.pdf
 		 */
 
 		/* Get the step size to be used when decoding the given sample. */
-		int stepSize = ima_step_size_table[prevStep[channel]] & 0x0000FFFF;
+		final int stepSize = ima_step_size_table[prevStep[channel]] & 0x0000FFFF;
 
 		/* This variable acts as 'difference' and then 'newSample' on columbia's doc */
-		int decodedSample = (stepSize >> 3) & 0x1fff;
+		int decodedSample = 0;
 
 		/* 
 		 * Similar to cs.columbia doc's first code block on Page 32, multiplication through 
 		 * repetitive addition. Nowadays using multiplication is probably faster on most archs, 
 		 * but let's follow the reference implementation for the sake of improving documentation.
 		 */
 		if ((adpcmSample & 4) != 0) { decodedSample += stepSize; }
-		if ((adpcmSample & 2) != 0) { decodedSample += (stepSize >> 1) & 0x7fff; }
-		if ((adpcmSample & 1) != 0) { decodedSample += (stepSize >> 2) & 0x3fff; }
+		if ((adpcmSample & 2) != 0) { decodedSample += stepSize >> 1; }
+		if ((adpcmSample & 1) != 0) { decodedSample += stepSize >> 2; }
+
+		decodedSample += stepSize >> 3;
+
 		if ((adpcmSample & 8) != 0) { decodedSample  = -decodedSample; }
 
 		decodedSample += prevSample[channel];
@@ -232,12 +235,12 @@ static short decodeSample(final byte channel, byte adpcmSample)
 		prevSample[channel] = decodedSample;
 
 		/* Basically columbia doc's "calculate stepsize" snippet */
-		prevStep[channel] += ima_step_index_table[(int)(adpcmSample & 0x0FF)];
+		prevStep[channel] += ima_step_index_table[adpcmSample];
 		if (prevStep[channel] < 0)       { prevStep[channel] = 0; }
 		else if (prevStep[channel] > 88) { prevStep[channel] = 88; }
 
 		/* Return the decoded sample casted to short (16-bit) */
-		return (short) (decodedSample & 0xFFFF);
+		return (short) (decodedSample);
 	}
 
 	/*
@@ -247,7 +250,7 @@ static short decodeSample(final byte channel, byte adpcmSample)
 	 * Optionally it also returns some information about the audio format to help build a 
 	 * new header for the decoded stream.
 	*/
-	public int[] readHeader(InputStream input) throws IOException 
+	public final int[] readHeader(InputStream input) throws IOException 
 	{
 		/*
 			The header of a WAV (RIFF) file is 44 bytes long and has the following format:
@@ -313,26 +316,26 @@ UINT16 BitsPerSample (gameloft games appear to use 4)
 	}
 
 	/* Read a 16-bit little-endian unsigned integer from input.*/
-	public static int readInputStreamInt16(InputStream input) throws IOException 
+	private static final int readInputStreamInt16(InputStream input) throws IOException 
 	{ return ( input.read() & 0xFF ) | ( ( input.read() & 0xFF ) << 8 ); }
 
 	/* Read a 32-bit little-endian signed integer from input.*/
-	public static int readInputStreamInt32(InputStream input) throws IOException 
+	private static final int readInputStreamInt32(InputStream input) throws IOException 
 	{
 		return ( input.read() & 0xFF ) | ( ( input.read() & 0xFF ) << 8 )
 			| ( ( input.read() & 0xFF ) << 16 ) | ( ( input.read() & 0xFF ) << 24 );
 	}
 
 	/* Return a String containing 'n' Characters of ASCII/ISO-8859-1 text from input. */
-	public static String readInputStreamASCII(InputStream input, int nChars) throws IOException 
+	private static final String readInputStreamASCII(InputStream input, int nChars) throws IOException 
 	{
 		byte[] chars = new byte[nChars];
 		readInputStreamData(input, chars, 0, nChars);
 		return new String(chars, "ISO-8859-1");
 	}
 
 	/* Read 'n' Bytes from the InputStream starting from the specified offset into the output array. */
-	public static void readInputStreamData(InputStream input, byte[] output, int offset, int nBytes) throws IOException 
+	private static final void readInputStreamData(InputStream input, byte[] output, int offset, int nBytes) throws IOException 
 	{
 		int end = offset + nBytes;
 		while(offset < end) 
@@ -347,7 +350,7 @@ public static void readInputStreamData(InputStream input, byte[] output, int off
 	 * Builds a WAV header that describes the decoded ADPCM file on the first 44 bytes. 
 	 * Data: little-endian, 16-bit, signed, same sample rate and channels as source IMA ADPCM.
 	 */
-	private void buildHeader(final byte[] buffer, final short numChannels, final int sampleRate) 
+	private final void buildHeader(final byte[] buffer, final short numChannels, final int sampleRate) 
 	{ 
 		final short bitsPerSample = 16;   /* 16-bit PCM */
 		final short audioFormat = 1;      /* WAV linear PCM */
@@ -414,7 +417,7 @@ private void buildHeader(final byte[] buffer, final short numChannels, final int
 	}
 
 	/* Decode the received IMA WAV ADPCM stream into a signed PCM16LE byte array, then return it to PlatformPlayer. */
-	public ByteArrayInputStream decodeImaAdpcm(InputStream stream, int[] wavHeaderData) throws IOException
+	public final ByteArrayInputStream decodeImaAdpcm(final InputStream stream, final int[] wavHeaderData) throws IOException
 	{
 		/* Remove the header from the stream, we shouldn't "decode" it as if it was a sample */
 		readHeader(stream);