SkippableComposition.java

/**
 * This is code is released under the
 * Apache License Version 2.0 http://www.apache.org/licenses/.
 *
 * (c) Daniel Lemire, http://lemire.me/en/
 */
package me.lemire.integercompression;


/**
 * Helper class to compose schemes.
 * 
 * @author Daniel Lemire
 */
public class SkippableComposition implements SkippableIntegerCODEC {
    SkippableIntegerCODEC F1, F2;

    /**
     * Compose a scheme from a first one (f1) and a second one (f2). The first
     * one is called first and then the second one tries to compress whatever
     * remains from the first run.
     * 
     * By convention, the first scheme should be such that if, during decoding,
     * a 32-bit zero is first encountered, then there is no output.
     * 
     * @param f1
     *            first codec
     * @param f2
     *            second codec
     */
    public SkippableComposition(SkippableIntegerCODEC f1,
            SkippableIntegerCODEC f2) {
        F1 = f1;
        F2 = f2;
    }

    @Override
    public void headlessCompress(int[] in, IntWrapper inpos, int inlength, int[] out,
            IntWrapper outpos) {
        int init = inpos.get();
        int outposInit = outpos.get();
        F1.headlessCompress(in, inpos, inlength, out, outpos);
        if (outpos.get() == outposInit) {
            out[outposInit] = 0;
            outpos.increment();
        }
        inlength -= inpos.get() - init;
        F2.headlessCompress(in, inpos, inlength, out, outpos);
    }

    @Override
    public void headlessUncompress(int[] in, IntWrapper inpos, int inlength, int[] out,
            IntWrapper outpos, int num) {
        int init = inpos.get();
        F1.headlessUncompress(in, inpos, inlength, out, outpos, num);
        if (inpos.get() == init) {
              inpos.increment();
        }
        inlength -= inpos.get() - init;
        num -= outpos.get();
        F2.headlessUncompress(in, inpos, inlength, out, outpos, num);
    }

    @Override
    public int maxHeadlessCompressedLength(IntWrapper compressedPositions, int inlength) {
        int init = compressedPositions.get();
        int maxLength = F1.maxHeadlessCompressedLength(compressedPositions, inlength);
        maxLength += 1; // Add +1 for the potential F2 header. Question: is this header actually needed in the headless version?
        inlength -= compressedPositions.get() - init;
        maxLength += F2.maxHeadlessCompressedLength(compressedPositions, inlength);
        return maxLength;
    }

    @Override
    public String toString() {
        return F1.toString() + "+" + F2.toString();
    }

}