package com.amazonaws.lex.twilio.sample.server.media;

/**
 * referenced from http://thorntonzone.com/manuals/Compression/Fax,%20IBM%20MMR/MMSC/mmsc/uk/co/mmscomputing/sound/CompressInputStream.java
 * <p>
 * Any credit for this work solely belongs to the original author of this code.
 * <p>
 * Do not use this class in production
 */
public class ALawCompressor extends Compressor {

    static final int cClip = 32635;

    static final int[] ALawCompressTable = {
            1, 1, 2, 2, 3, 3, 3, 3,
            4, 4, 4, 4, 4, 4, 4, 4,
            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,
            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
    };

    protected int compress(short sample) {
        int sign;
        int exponent;
        int mantissa;
        int compressedByte;

        sign = ((~sample) >> 8) & 0x80;
        if (sign == 0) {
            sample *= -1;
        }
        if (sample > cClip) {
            sample = cClip;
        }
        if (sample >= 256) {
            exponent = ALawCompressTable[(sample >> 8) & 0x007F];
            mantissa = (sample >> (exponent + 3)) & 0x0F;
            compressedByte = 0x007F & ((exponent << 4) | mantissa);
        } else {
            compressedByte = 0x007F & (sample >> 4);
        }
        compressedByte ^= (sign ^ 0x55);
        return compressedByte;
    }
}