150 lines
4.0 KiB
Plaintext
150 lines
4.0 KiB
Plaintext
== cmph - C Minimal Perfect Hashing Library ==
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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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work with minimal perfect hashes. The cmph library encapsulates the newest
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and more efficient algorithms in the literature in a ease-to-use,
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production-quality, fast API. The library is designed to work big entries that
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won't fit in the main memory. It has been used successfully to create hashes
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bigger than 100 million entries. Although there is a lack of similar libraries
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in the free software world, we can point out some of the "distinguishing"
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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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- Object oriented implementation
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- Works with in-disk key sets through use of adapter pattern
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- Serialization of hash functions
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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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**News for version 0.3**
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- New heuristics in bmz algorithm, providing hash creation with only
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(0.93 * 16 + 4)*n bytes and hash query with (0.93*4)n bytes
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**Examples**
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Using cmph is quite ease. Take a look.
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```
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// Create minimal perfect hash 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 hash
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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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-------------------------------
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```
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// Create minimal perfect hash 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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--------------------------------------
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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 to create minimal perfect hashes from command line. The cmph utility
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comes with a number of flags, but it is very simple to create and query
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minimal perfect hashes:
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```
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$ # Create mph for keys in file keys_file
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$ ./cmph 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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```
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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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```
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usage: cmph [-v] [-h] [-V] [-k] [-g [-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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* czech
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* bmz
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-f hash function (may be used multiple times) - valid values are
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* jenkins
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* djb2
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* sdbm
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* fnv
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* glib
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* pjw
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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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```
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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: %%date(%c)
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