private final boolean tableFull( int reprobe_cnt, int len ) {
      return
        // Do the cheap check first: we allow some number of reprobes always
        reprobe_cnt >= REPROBE_LIMIT &&
        // More expensive check: see if the table is > 1/4 full.
        _slots.estimate_get() >= reprobe_limit(len);
    }
Returns the value to which the specified key is mapped, or {@code null}
 if this map contains no mapping for the key.
 <p>More formally, if this map contains a mapping from a key {@code k} to
 a value {@code v} such that {@code key.equals(k)}, then this method
 returns {@code v}; otherwise it returns {@code null}.  (There can be at
 most one such mapping.)
@throws NullPointerException if the specified key is null
jctools-core/src/main/java/org/jctools/maps/NonBlockingIdentityHashMap.java