Codec for creating a split double range

CodecMapping.java

/*
 * This codec creates a split range, where only values between [0, 2) and
 * [8, 10) are valid. The valid range is marked with '-' and the invalid
 * range with 'x'.
 *
 *   +--+--+--+--+--+--+--+--+--+--+
 *   |  |  |  |  |  |  |  |  |  |  |
 *   0  1  2  3  4  5  6  7  8  9  10
 *   |-----|xxxxxxxxxxxxxxxxx|-----|
 *      ^  |llllllll|rrrrrrrr|  ^
 *      |       |        |      |
 *      +-------+        +------+
 *
 * The mapping function maps the left part of the invalid range, denoted
 * with 'l', to the lower valid range. The upper half of the invalid range,
 * 'r', is mapped to the upper valid range. This way we have created a more
 * complex codec by using an existing one.
 * If you want to get the best value back from the best genotype, you have
 * to decode it using the same codec.
 *
 * final Genotype<DoubleGene> gt = stream
 *     .limit(100)
 *     .collect(EvolutionResult.toBestGenotype());
 *
 * final double bestValue = CODEC.decode(gt);
 */
private static final Codec<Double, DoubleGene> CODEC = Codecs
	.ofScalar(DoubleRange.of(0, 10))
	.map((Double v) -> {
			if (v >= 2 && v < 8) {
				return v < 5 ? ((v - 2)/3)*2 : ((8 - v)/3)*2 + 8;
			}
			return v;
		});