private static boolean exactMode(long packMin, long packMax) {
        return (packMax - packMin) <= PACK_HIST_SIZE_BIT - 2;
    }
Each pack (with 65536 values), we use 128 bytes, i.e. 1024 bits to index.
indexr-segment/src/main/java/io/indexr/segment/index/RSIndex_Histogram.java