171 lines
5.1 KiB
Plaintext
171 lines
5.1 KiB
Plaintext
CMPH - C Minimal Perfect Hashing Library
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-------------------------------------------------------------------
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Description
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C Minimal Perfect Hashing Library is a portable LGPLed library to create and
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to work with minimal perfect hashing functions. The cmph library encapsulates the newest
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and more efficient algorithms (available in the literature) in an easy-to-use,
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production-quality and fast API. The library is designed to work with big entries that
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can not fit in the main memory. It has been used successfully for constructing minimal perfect
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hashing functions for sets with more than 100 million of keys.
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Although there is a lack of similar libraries
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in the free software world (gperf is a bit different (gperf.html)), we can point out some
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of the distinguishable features of cmph:
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- Fast.
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- Space-efficient with main memory usage carefully documented.
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- The best modern algorithms are available (or at least scheduled for implementation :-)).
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- Works with in-disk key sets through of using the adapter pattern.
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- Serialization of hash functions.
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- Portable C code (currently works on GNU/Linux and WIN32).
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- Object oriented implementation.
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- Easily extensible.
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- Well encapsulated API aiming binary compatibility through releases.
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- Free Software.
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----------------------------------------
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Supported Algorithms
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- BMZ Algorithm.
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A very fast algorithm based on cyclic random graphs to construct minimal
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perfect hash functions in linear time. The resulting functions are not order preserving and
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can be stored in only 4cn bytes, where c is between 0.93 and 1.15.
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- CHM Algorithm.
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An algorithm based on acyclic random graphs to construct minimal
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perfect hash functions in linear time. The resulting functions are order preserving and
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are stored in 4cn bytes, where c is greater than 2.
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----------------------------------------
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News for version 0.3
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- New heuristic added to the bmz algorithm permits to generate a mphf with only
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24.61*n + O(1) bytes. The resulting function can be stored in 3.72*n bytes.
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click here (bmz.html) for details.
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----------------------------------------
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Examples
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Using cmph is quite simple. Take a look.
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// Create minimal perfect hash function from in-memory vector
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#include <cmph.h>
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...
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const char **vector;
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unsigned int nkeys;
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//Fill vector
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//...
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//Create minimal perfect hashing function using the default(chm) algorithm.
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cmph_config_t *config = cmph_config_new(cmph_io_vector_adapter(vector, nkeys));
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cmph_t *hash = cmph_new(config);
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cmph_config_destroy(config);
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//Find key
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const char *key = "sample key";
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unsigned int id = cmph_search(hash, key);
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//Destroy hash
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cmph_destroy(hash);
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-------------------------------
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// Create minimal perfect hash function from in-disk keys using BMZ algorithm
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#include <cmph.h>
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...
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//Open file with newline separated list of keys
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FILE *fd = fopen("keysfile_newline_separated", "r");
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//check for errors
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//...
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cmph_config_t *config = cmph_config_new(cmph_io_nlfile_adapter(fd));
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cmph_config_set_algo(config, CMPH_BMZ);
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cmph_t *hash = cmph_new(config);
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cmph_config_destroy(config);
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fclose(fd);
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//Find key
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const char *key = "sample key";
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unsigned int id = cmph_search(hash, key);
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//Destroy hash
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cmph_destroy(hash);
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--------------------------------------
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The cmph application
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cmph is the name of both the library and the utility
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application that comes with this package. You can use the cmph
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application for constructing minimal perfect hashing functions from the command line.
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The cmph utility
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comes with a number of flags, but it is very simple to create and to query
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minimal perfect hashing functions:
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$ # Using the chm algorithm (default one) for constructing a mphf for keys in file keys_file
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$ ./cmph -g keys_file
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$ # Query id of keys in the file keys_query
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$ ./cmph -m keys_file.mph keys_query
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The additional options let you set most of the parameters you have
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available through the C API. Below you can see the full help message for the
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utility.
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usage: cmph [-v] [-h] [-V] [-k nkeys] [-f hash_function] [-g [-c value][-s seed] ] [-m file.mph] [-a algorithm] keysfile
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Minimum perfect hashing tool
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-h print this help message
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-c c value that determines the number of vertices in the graph
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-a algorithm - valid values are
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* bmz
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* chm
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-f hash function (may be used multiple times) - valid values are
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* djb2
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* fnv
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* glib
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* jenkins
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* pjw
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* sdbm
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-V print version number and exit
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-v increase verbosity (may be used multiple times)
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-k number of keys
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-g generation mode
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-s random seed
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-m minimum perfect hash function file
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keysfile line separated file with keys
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Downloads
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Use the project page at sourceforge: http://sf.net/projects/cmph
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License Stuff
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Code is under the LGPL.
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----------------------------------------
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Enjoy!
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Davi de Castro Reis
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Fabiano Cupertino Botelho
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Last Updated: Wed Jan 26 22:37:36 2005
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