package ivory.lsh.data;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;

import org.apache.hadoop.io.Writable;

/**
 * A data structure to optimize space when storing an array of floats.
 * Floats are quantized into byte values and stored as a BytesWritable.
 * maxNorm is a maxNormalization factor required to re-compute float from byte.
 * 
 * byte = quantize(float) = ((float/maxNorm)*128)==128 ? 127 : ((float/maxNorm)
 * float = dequantize(byte) = ((byte/128)*maxNorm)
 * 
 * @author ferhanture
 *
 */
public class FloatAsBytesWritable implements Writable{
  byte[] bytes;
  float maxNorm, minNorm;

  public FloatAsBytesWritable() {
    super();
  }

  public FloatAsBytesWritable(byte[] bytearray, float max, float min) {
    super();
    bytes = new byte[bytearray.length];
    for(int i=0;i<bytearray.length;i++){
      bytes[i]=bytearray[i];
    }
    maxNorm = max;
    minNorm = min;
  }

  public void readFields(DataInput in) throws IOException {
    maxNorm = in.readFloat();
    minNorm = in.readFloat();
    bytes = new byte[in.readInt()];
    for(int i=0;i<bytes.length;i++){
      bytes[i] = in.readByte();
    }
  }

  public void write(DataOutput out) throws IOException {
    out.writeFloat(maxNorm);
    out.writeFloat(minNorm);
    out.writeInt(bytes.length);
    for(int i=0;i<bytes.length;i++){
      out.writeByte(bytes[i]);
    }
  }

  public byte get(int index){
    return bytes[index];
  }

  public float getAsFloat(int index){
    byte f1 = get(index);
    if(f1>0){
      return ((float)f1*maxNorm/128f);
    }else{			
      return ((float)-f1*minNorm/128f);
    }
  }

  public int size() {
    return bytes.length;
  }

}