Editing Hash function (section)

=== Middle and ends ===
Simplistic hash functions may add the first and last {{math|''n''}} characters of a string along with the length, or form a word-size hash from the middle 4 characters of a string.  This saves iterating over the (potentially long) string, but hash functions that do not hash on all characters of a string can readily become linear due to redundancies, clustering, or other pathologies in the key set.  Such strategies may be effective as a custom hash function if the structure of the keys is such that either the middle, ends, or other fields are zero or some other invariant constant that does not differentiate the keys; then the invariant parts of the keys can be ignored.