DeltaZigzagBinaryPacking.java

/*
 * This code is released under the
 * Apache License Version 2.0 http://www.apache.org/licenses/.
 */

package me.lemire.integercompression;

/**
 * BinaryPacking with Delta+Zigzag Encoding.
 * 
 * It encodes integers in blocks of 128 integers. For arrays containing
 * an arbitrary number of integers, you should use it in conjunction
 * with another CODEC: 
 * 
 *  <pre>IntegerCODEC ic = new Composition(new DeltaZigzagBinaryPacking(),
 *                      new DeltaZigzagVariableByte()).</pre>
 * 
 * @author MURAOKA Taro http://github.com/koron
 */
public final class DeltaZigzagBinaryPacking implements IntegerCODEC {

        private static final int BLOCK_LENGTH = 128;

        @Override
        public void compress(int[] inBuf, IntWrapper inPos, int inLen,
                int[] outBuf, IntWrapper outPos) {
                inLen = inLen - inLen % BLOCK_LENGTH;
                if (inLen == 0) {
                        return;
                }

                outBuf[outPos.get()] = inLen;
                outPos.increment();

                DeltaZigzagEncoding.Encoder ctx = new DeltaZigzagEncoding.Encoder(0);
                int[] work = new int[BLOCK_LENGTH];

                int op = outPos.get();
                int ip = inPos.get();
                final int inPosLast = ip + inLen;
                for (; ip < inPosLast; ip += BLOCK_LENGTH) {
                        ctx.encodeArray(inBuf, ip, BLOCK_LENGTH, work);
                        final int bits1 = Util.maxbits32(work, 0);
                        final int bits2 = Util.maxbits32(work, 32);
                        final int bits3 = Util.maxbits32(work, 64);
                        final int bits4 = Util.maxbits32(work, 96);
                        outBuf[op++] = (bits1 << 24) | (bits2 << 16)
                                | (bits3 << 8) | (bits4 << 0);
                        op += pack(work, 0, outBuf, op, bits1);
                        op += pack(work, 32, outBuf, op, bits2);
                        op += pack(work, 64, outBuf, op, bits3);
                        op += pack(work, 96, outBuf, op, bits4);
                }

                inPos.add(inLen);
                outPos.set(op);
        }

        @Override
        public void uncompress(int[] inBuf, IntWrapper inPos, int inLen,
                int[] outBuf, IntWrapper outPos) {
                if (inLen == 0) {
                        return;
                }

                final int outLen = inBuf[inPos.get()];
                inPos.increment();

                DeltaZigzagEncoding.Decoder ctx = new DeltaZigzagEncoding.Decoder(0);
                int[] work = new int[BLOCK_LENGTH];

                int ip = inPos.get();
                int op = outPos.get();
                final int outPosLast = op + outLen;
                for (; op < outPosLast; op += BLOCK_LENGTH) {
                        int n = inBuf[ip++];
                        ip += unpack(inBuf, ip, work, 0, (n >> 24) & 0x3F);
                        ip += unpack(inBuf, ip, work, 32, (n >> 16) & 0x3F);
                        ip += unpack(inBuf, ip, work, 64, (n >> 8) & 0x3F);
                        ip += unpack(inBuf, ip, work, 96, (n >> 0) & 0x3F);
                        ctx.decodeArray(work, 0, BLOCK_LENGTH, outBuf, op);
                }

                outPos.add(outLen);
                inPos.set(ip);
        }

        private static int pack(int[] inBuf, int inOff, int[] outBuf,
                int outOff, int validBits) {
                BitPacking.fastpackwithoutmask(inBuf, inOff, outBuf, outOff,
                        validBits);
                return validBits;
        }

        private static int unpack(int[] inBuf, int inOff, int[] outBuf,
                int outOff, int validBits) {
                BitPacking.fastunpack(inBuf, inOff, outBuf, outOff, validBits);
                return validBits;
        }

        @Override
        public String toString() {
                return this.getClass().getSimpleName();
        }
}