GPERF versus CMPH



You might ask why cmph if [gperf http://www.gnu.org/software/gperf/gperf.html] 
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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Davi de Castro Reis

Fabiano Cupertino Botelho