== cmph - C Minimal Perfect Hashing Library ==
**Description**
C Minimal Perfect Hashing Library is a portable LGPLed library to create and
work with minimal perfect hashes. The cmph library encapsulates the newest
and more efficient algorithms in the literature in a ease-to-use,
production-quality, fast API. The library is designed to work big entries that
won't fit in the main memory. It has been used successfully to create hashes
bigger than 100 million entries. Although there is a lack of similar libraries
in the free software world, we can point out some of the "distinguishing"
features of cmph:
- Fast
- Space-efficient with main memory usage carefully documented
- The best modern algorithms are available (or at least scheduled for implementation :-))
- Works with in-disk key sets through use of adapter pattern
- Serialization of hash functions
- Portable C code (currently works on GNU/Linux and WIN32)
- Object oriented implementation
- Easily extensible
- Well encapsulated API aiming binary compatibility through releases
- Free Software
**News for version 0.3**
- New heuristics in bmz algorithm, providing hash creation with only
(0.93 * 16 + 4)*n bytes and hash query with (0.93*4)n bytes
**Examples**
Using cmph is quite ease. Take a look.
```
// Create minimal perfect hash from in-memory vector
#include <cmph.h>
...
const char **vector;
unsigned int nkeys;
//Fill vector
//...
//Create minimal perfect hash
cmph_config_t *config = cmph_config_new(cmph_io_vector_adapter(vector, nkeys));
cmph_t *hash = cmph_new(config);
cmph_config_destroy(config);
//Find key
const char *key = "sample key";
unsigned int id = cmph_search(hash, key);
//Destroy hash
cmph_destroy(hash);
```
-------------------------------
```
// Create minimal perfect hash from in-disk keys using BMZ algorithm
#include <cmph.h>
...
//Open file with newline separated list of keys
FILE *fd = fopen("keysfile_newline_separated", "r");
//check for errors
//...
cmph_config_t *config = cmph_config_new(cmph_io_nlfile_adapter(fd));
cmph_config_set_algo(config, CMPH_BMZ);
cmph_t *hash = cmph_new(config);
cmph_config_destroy(config);
fclose(fd);
//Find key
const char *key = "sample key";
unsigned int id = cmph_search(hash, key);
//Destroy hash
cmph_destroy(hash);
```
--------------------------------------
**The cmph application**
cmph is the name of both the library and the utility
application that comes with this package. You can use the cmph
application to create minimal perfect hashes from command line. The cmph utility
comes with a number of flags, but it is very simple to create and query
minimal perfect hashes:
```
$ # Create mph for keys in file keys_file
$ ./cmph keys_file
$ # Query id of keys in the file keys_query
$ ./cmph -m keys_file.mph keys_query
```
The additional options let you set most of the parameters you have
available through the C API. Below you can see the full help message for the
utility.
```
usage: cmph [-v] [-h] [-V] [-k] [-g [-s seed] ] [-m file.mph] [-a algorithm] keysfile
Minimum perfect hashing tool
-h print this help message
-c c value that determines the number of vertices in the graph
-a algorithm - valid values are
* czech
* bmz
-f hash function (may be used multiple times) - valid values are
* jenkins
* djb2
* sdbm
* fnv
* glib
* pjw
-V print version number and exit
-v increase verbosity (may be used multiple times)
-k number of keys
-g generation mode
-s random seed
-m minimum perfect hash function file
keysfile line separated file with keys
```
**Downloads**
Use the project page at sourceforge: http://sf.net/projects/cmph
**License Stuff**
Code is under the LGPL.
----------------------------------------
Enjoy!
Davi de Castro Reis
Fabiano Cupertino Botelho
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Last Updated: %%date(%c)
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