# GPERF versus CMPH

You might ask why cmph if gperf already works perfectly. Actually, gperf and cmph have different goals. Basically, these are the requirements for each of them:

- GPERF

> - Create very fast hash functions for small sets

> - Create perfect hash functions

- CMPH

> - Create very fast hash function for very large sets

> - Create minimal perfect hash functions

As result, cmph can be used to create hash functions where gperf would run forever without finding a perfect hash function, because of the running time of the algorithm and the large memory usage. On the other side, functions created by cmph are about 2x slower than those created by gperf.

So, if you have large sets, or memory usage is a key restriction for you, stick to cmph. If you have small sets, and do not care about memory usage, go with gperf. The first problem is common in the information retrieval field (e.g. assigning ids to millions of documents), while the former is usually found in the compiler programming area (detect reserved keywords).

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Enjoy!

Davi de Castro Reis

Djamel Belazzougui

Fabiano Cupertino Botelho

Nivio Ziviani