Mapping function

Question

I have a set of 128bit number and the size of set < 2^32 ...so theoretically I can have a mapping function that maps all the 128bit numbers to 32 bit number ....how can I construct the mapping function ???

Answer 1

Seems like you are looking for a minimal perfect hash which maps n keys to n consecutive integers.

The wiki page link in the above sentence mentions two libraries which implement this.

Also see this for more detail: http://burtleburtle.net/bob/hash/perfect.html