bucket: Map<Bits, IntArray> = ...

fun getEntities(aspect: Aspect): IntArray {
    var result = HashMap<Bits, IntArray>()

    // 1st pass, "allOf"
    if (aspect.required == Bits.ZERO) {
        result.addAll(bucket)
    } else {
        bucket.forEach { (bits, entities) ->
            if (bits AND aspect.required == aspect.required) {
                result.add(bits, entities)
            }
        }
    }

    // 2nd pass, "anyOf"
    if (aspect.optional != Bits.ZERO) {
        result = result.filter { (bits, entities) ->
            bits AND aspect.optional != Bits.ZERO
        }.toMap()
    }

    // 3rd pass, "excluding"
    if (aspect.excluded != Bits.ZERO) {
        result = result.filter { (bits, entities) ->
            bits AND aspect.excluded == Bits.ZERO
        }
    }

    return result.values().reduce {base, next -> ...}
}