private static boolean exactMode(long packMin, long packMax) {
        return (packMax - packMin) <= PACK_HISTO_SIZE_BIT - 2;
    }
Hash + Histogram, each takes 1024 bits.

| hash index0 | histo index0 | hash index1 | histo index1 | ...
|  1024 bits  |  1024 bits   |  1024 bits  |  1024 bits   | ...
indexr-segment/src/main/java/io/indexr/segment/index/RSIndex_Histogram_V2.java