public static long readSignedVL(DataInput in) throws IOException {
    return decodeZigZag64(readUnsignedVL(in));
  }
Decode a signed long as a variable length array.

This method is appropriate for signed integers. It uses zig zag encoding to so that negative
numbers will be represented more compactly. For unsigned values, writeUnsignedVL will be more
efficient.
geode-core/src/main/java/org/apache/geode/internal/InternalDataSerializer.java