guava/src/com/google/common/collect/MapMakerInternalMap.java
Segment<K, V, E, S> segmentFor(int hash) {
    // TODO(fry): Lazily create segments?
    return segments[(hash >>> segmentShift) & segmentMask];
  }
Segment<K, V, E, S> segmentFor(int hash) {
    // TODO(fry): Lazily create segments?
    return segments[(hash >>> segmentShift) & segmentMask];
  }
Returns the segment that should be used for a key with the given hash.

@param hash the hash code for the key
@return the segment