core/java/android/speech/srec/UlawEncoderInputStream.java

/*
 * ---------------------------------------------------------------------------
 * UlawEncoderInputStream.java
 *
 * Copyright 2008 Nuance Communciations, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the 'License'); you may not
 * use this file except in compliance with the License.
 *
 * You may obtain a copy of the License at
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an 'AS IS' BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 *
 * ---------------------------------------------------------------------------
 */

package android.speech.srec;

import java.io.IOException;
import java.io.InputStream;

/**
 * InputStream which transforms 16 bit pcm data to ulaw data.
 * 
 * Not yet ready to be supported, so
 * @hide
 */
public final class UlawEncoderInputStream extends InputStream {
    private final static String TAG = "UlawEncoderInputStream";
    
    private final static int MAX_ULAW = 8192;
    private final static int SCALE_BITS = 16;
    
    private InputStream mIn;
    
    private int mMax = 0;
    
    private final byte[] mBuf = new byte[1024];
    private int mBufCount = 0; // should be 0 or 1
    
    private final byte[] mOneByte = new byte[1];

    
    public static void encode(byte[] pcmBuf, int pcmOffset,
            byte[] ulawBuf, int ulawOffset, int length, int max) {
        
        // from  'ulaw' in wikipedia
        // +8191 to +8159                          0x80
        // +8158 to +4063 in 16 intervals of 256   0x80 + interval number
        // +4062 to +2015 in 16 intervals of 128   0x90 + interval number
        // +2014 to  +991 in 16 intervals of  64   0xA0 + interval number
        //  +990 to  +479 in 16 intervals of  32   0xB0 + interval number
        //  +478 to  +223 in 16 intervals of  16   0xC0 + interval number
        //  +222 to   +95 in 16 intervals of   8   0xD0 + interval number
        //   +94 to   +31 in 16 intervals of   4   0xE0 + interval number
        //   +30 to    +1 in 15 intervals of   2   0xF0 + interval number
        //     0                                   0xFF
        
        //    -1                                   0x7F
        //   -31 to    -2 in 15 intervals of   2   0x70 + interval number
        //   -95 to   -32 in 16 intervals of   4   0x60 + interval number
        //  -223 to   -96 in 16 intervals of   8   0x50 + interval number
        //  -479 to  -224 in 16 intervals of  16   0x40 + interval number
        //  -991 to  -480 in 16 intervals of  32   0x30 + interval number
        // -2015 to  -992 in 16 intervals of  64   0x20 + interval number
        // -4063 to -2016 in 16 intervals of 128   0x10 + interval number
        // -8159 to -4064 in 16 intervals of 256   0x00 + interval number
        // -8192 to -8160                          0x00
        
        // set scale factors
        if (max <= 0) max = MAX_ULAW;
        
        int coef = MAX_ULAW * (1 << SCALE_BITS) / max;
        
        for (int i = 0; i < length; i++) {
            int pcm = (0xff & pcmBuf[pcmOffset++]) + (pcmBuf[pcmOffset++] << 8);
            pcm = (pcm * coef) >> SCALE_BITS;
            
            int ulaw;
            if (pcm >= 0) {
                ulaw = pcm <= 0 ? 0xff :
                        pcm <=   30 ? 0xf0 + ((  30 - pcm) >> 1) :
                        pcm <=   94 ? 0xe0 + ((  94 - pcm) >> 2) :
                        pcm <=  222 ? 0xd0 + (( 222 - pcm) >> 3) :
                        pcm <=  478 ? 0xc0 + (( 478 - pcm) >> 4) :
                        pcm <=  990 ? 0xb0 + (( 990 - pcm) >> 5) :
                        pcm <= 2014 ? 0xa0 + ((2014 - pcm) >> 6) :
                        pcm <= 4062 ? 0x90 + ((4062 - pcm) >> 7) :
                        pcm <= 8158 ? 0x80 + ((8158 - pcm) >> 8) :
                        0x80;
            } else {
                ulaw = -1 <= pcm ? 0x7f :
                          -31 <= pcm ? 0x70 + ((pcm -   -31) >> 1) :
                          -95 <= pcm ? 0x60 + ((pcm -   -95) >> 2) :
                         -223 <= pcm ? 0x50 + ((pcm -  -223) >> 3) :
                         -479 <= pcm ? 0x40 + ((pcm -  -479) >> 4) :
                         -991 <= pcm ? 0x30 + ((pcm -  -991) >> 5) :
                        -2015 <= pcm ? 0x20 + ((pcm - -2015) >> 6) :
                        -4063 <= pcm ? 0x10 + ((pcm - -4063) >> 7) :
                        -8159 <= pcm ? 0x00 + ((pcm - -8159) >> 8) :
                        0x00;
            }
            ulawBuf[ulawOffset++] = (byte)ulaw;
        }
    }
    
    /**
     * Compute the maximum of the absolute value of the pcm samples.
     * The return value can be used to set ulaw encoder scaling.
     * @param pcmBuf array containing 16 bit pcm data.
     * @param offset offset of start of 16 bit pcm data.
     * @param length number of pcm samples (not number of input bytes)
     * @return maximum abs of pcm data values
     */
    public static int maxAbsPcm(byte[] pcmBuf, int offset, int length) {
        int max = 0;
        for (int i = 0; i < length; i++) {
            int pcm = (0xff & pcmBuf[offset++]) + (pcmBuf[offset++] << 8);
            if (pcm < 0) pcm = -pcm;
            if (pcm > max) max = pcm;
        }
        return max;
    }

    /**
     * Create an InputStream which takes 16 bit pcm data and produces ulaw data.
     * @param in InputStream containing 16 bit pcm data.
     * @param max pcm value corresponding to maximum ulaw value.
     */
    public UlawEncoderInputStream(InputStream in, int max) {
        mIn = in;
        mMax = max;
    }
    
    @Override
    public int read(byte[] buf, int offset, int length) throws IOException {
        if (mIn == null) throw new IllegalStateException("not open");

        // return at least one byte, but try to fill 'length'
        while (mBufCount < 2) {
            int n = mIn.read(mBuf, mBufCount, Math.min(length * 2, mBuf.length - mBufCount));
            if (n == -1) return -1;
            mBufCount += n;
        }
        
        // compand data
        int n = Math.min(mBufCount / 2, length);
        encode(mBuf, 0, buf, offset, n, mMax);
        
        // move data to bottom of mBuf
        mBufCount -= n * 2;
        for (int i = 0; i < mBufCount; i++) mBuf[i] = mBuf[i + n * 2];
        
        return n;
    }
    
    @Override
    public int read(byte[] buf) throws IOException {
        return read(buf, 0, buf.length);
    }
    
    @Override
    public int read() throws IOException {
        int n = read(mOneByte, 0, 1);
        if (n == -1) return -1;
        return 0xff & (int)mOneByte[0];
    }
    
    @Override
    public void close() throws IOException {
        if (mIn != null) {
            InputStream in = mIn;
            mIn = null;
            in.close();
        }
    }
    
    @Override
    public int available() throws IOException {
        return (mIn.available() + mBufCount) / 2;
    }
}