dbh_genkey(3) DBHashTables Programmers' Manual dbh_genkey(3)
‐
NAME
dbh_genkey, dbh_genkey2, dbh_orderkey - generate cuantified or ordered
keys
SYNOPSIS
#include <dbh.h>
void dbh_genkey (unsigned char *key, unsigned char length, unsigned int
n);
void dbh_genkey2 (unsigned char *key, unsigned char length, unsigned
int n);
void dbh_orderkey (unsigned char *key, unsigned char length, unsigned
int n, unsigned char base);
DESCRIPTION
dbh_genkey and dbh_genkey2 obtain a key from a secuential series of
natural numbers (positive integers without zero) which does not con‐
serve the order of the natural numbers, but which are optimized for
construction of a balanced hash tree. In dbh_genkey the key is
expressed in cuantified numbers based on the 0 digit. In dbh_genkey2
the key is expressed in cuantified numbers based on the A symbol.
dbh_orderkey will obtain a key from a secuential series of natural num‐
bers (positive integers without zero) which conserves the order of the
natural numbers. This function generates a key that belongs to a finite
subset of the cuantified numbers, but which preserves the order of the
natural numbers (up to the supreme, of course).
In these functions key is pointer to the address where to put the gen‐
erated key, length is the key length, and n is the natural number for
which to generate the key. For dbh_orderkey base is the number system
base to use. This will equal the maximum number of nodes per branch.
This ---along with the keylength--- will define a maximum number of
records for the DBHashTable.
RETURN VALUE
These functions do not return any value.
NOTES
Cuantified numbers are an alternate way to view the set of natural num‐
bers {1, 2, 3, ...} where order is defined in two levels. In natural
numbers there is only one level of order (defined by the > boolean
operator). In cuantified numbers the first level of order is defined by
the cuanta or quantity. The cuanta is obtained by adding all the digits
of the cuantified number. Thus, for example, 10022, 5, 32, and 11111
are all equal at the first level of order since they all add up to 5.
The second level or order may be obtained in different manners. In
functions dbh_genkey and dbh_genkey2 the corresponding order of the
natural numbers from which they are associated is not conserved. In
dbh_orderkey the corresponding order of the natural numbers from which
they are associated is conserved, but at a price. The base, or maximum
value each digit may reach, must be defined. This effectively puts a
limit on the number of keys which may be generated for a given number
of digits.
When a DBHashTable is constructed with cuantified keys, the maximum
amount of disk access instructions generated to access any given record
is equal to the cuanta of the cuantified number represented by the key.
This allows a DBHashTable to be constructed with minimum access time
across all records.
SEE ALSO
dbh (0), dbh_update (3), dbh_load (3)
Author
Edscott Wilson Garcia <edscott@xfce.org>
DBHashTables DBH dbh_genkey(3)
