private static int hash(int h) {
        // Spread bits to regularize both segment and index locations,
        // using variant of single-word Wang/Jenkins hash.
        h += (h <<  15) ^ 0xffffcd7d;
        h ^= (h >>> 10);
        h += (h <<   3);
        h ^= (h >>>  6);
        h += (h <<   2) + (h << 14);
        return h ^ (h >>> 16);
    }
Applies a supplemental hash function to a given hashCode, which
defends against poor quality hash functions.  This is critical
because ConcurrentWeakHashMap uses power-of-two length hash tables,
that otherwise encounter collisions for hashCodes that do not
differ in lower or upper bits.
commons-profiler/src/main/java/com/navercorp/pinpoint/common/profiler/concurrent/jsr166/ConcurrentWeakHashMap.java