39 lines
1.2 KiB
Plaintext
39 lines
1.2 KiB
Plaintext
GPERF versus CMPH
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You might ask why cmph if [gperf http://www.gnu.org/software/gperf/gperf.html]
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already works perfectly. Actually, gperf and cmph have different goals.
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Basically, these are the requirements for each of them:
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- GPERF
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- Create very fast hash functions for **small** sets
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- Create **perfect** hash functions
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- CMPH
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- Create very fast hash function for **very large** sets
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- Create **minimal perfect** hash functions
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As result, cmph can be used to create hash functions where gperf would run
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forever without finding a perfect hash function, because of the running
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time of the algorithm and the large memory usage.
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On the other side, functions created by cmph are about 2x slower than those
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created by gperf.
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So, if you have large sets, or memory usage is a key restriction for you, stick
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to cmph. If you have small sets, and do not care about memory usage, go with
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gperf. The first problem is common in the information retrieval field (e.g.
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assigning ids to millions of documents), while the former is usually found in
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the compiler programming area (detect reserved keywords).
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