VarIntUtils.java

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package org.matsim.core.population.routes.heavycompressed;

import java.nio.ByteBuffer;

// inspired from https://github.com/nla/outbackcdx/blob/master/src/outbackcdx/VarInt.java
// licensed under the Apache 2 License.
// NO zig-zag encoding, NOT the same as protobuf varint! only for values >= 0

public class VarIntUtils {

    private static final byte[] EMPTY_BYTE = new byte[0];
    private static final int[] EMPTY_INT = new int[0];

    public static void encode(ByteBuffer bb, long x) {
        while (Long.compareUnsigned(x, 127) > 0) {
            bb.put((byte) (x & 127 | 128));
            x >>>= 7;
        }
        bb.put((byte) (x & 127));
    }

    public static long decode(ByteBuffer bb) {
        long x = 0;
        int shift = 0;
        long b;
        do {
            b = bb.get() & 0xff;
            x |= (b & 127) << shift;
            shift += 7;
        } while ((b & 128) != 0);
        return x;
    }

    public static byte[] encode(int[] values, int lower, int upper) {
        if (values.length == 0) {
            return EMPTY_BYTE;
        }
        ByteBuffer bb = ByteBuffer.allocate(5 * values.length + 5);
        encode(bb, upper - lower);
        for (int i = lower; i < upper; i++) {
            encode(bb, values[i]);
        }
        byte[] bytes = bb.array();
        byte[] trimmed = new byte[bb.position()];
        System.arraycopy(bytes, 0, trimmed, 0, bb.position());
        return trimmed;
    }

    public static int[] decode(byte[] bytes) {
        if (bytes.length == 0) {
            return EMPTY_INT;
        }
        ByteBuffer bb = ByteBuffer.wrap(bytes);
        int length = (int) decode(bb);
        int[] values = new int[length];
        for (int i = 0; i < length; i++) {
            values[i] = (int) decode(bb);
        }
        return values;
    }

}