Semiconductor & Computer Engineering
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Revision as of 23:05, 2 December 2013
The /hmake command can be used to create a new hash table by a specific handle name.
A hash table is stored entirely in memory and thus it is the programmer's responsibility to save the data to a file if necessary via the /hsave command (and load it back later via the /hload command).
The number of buckets is always made to be a prime number before the hash table is created. If [num_buckets] is an even number, mIRC will add one to the number. The range of buckets is between 1 and 10000, making the final capacity between 1 and 10001. A hash table name is limited to 256 significant characters - any additional characters are simply ignored. In mIRC, a hash table is a much faster alternative to ini and normal text files.
Note: For most practical purposes, it's best to keep the ratio of <item count>:<maximum capacity> at 78% to maintain a good time-space tradeoff (i.e. 0.78 load factor). That means if you are planning on storing 78 items in the hash table, you should create a hash table with the size of 100 buckets. (A table of 1000 buckets is good to store up to about 780 items to maintain a maximum performance). The general equation to calculate optimal number of buckets is:
[#_of_buckets] = [#_of_keys_that_will_be_used] / 0.78
Linked List
Because the hash table uses chaining to resolve collisions and due to the fact mIRC does not rehash or grows the array, using a hash table with 1 bucket, the hmake command can be used to create a linked list. New items are added to the start of the chain (i.e. $hget(<table_name>, 1) will always be last item added). Additionally, changing the value or removing an item does not alter the overall order of the list.
Synopsis
/hmake [-s] <table_name> [num_buckets]
Switches
- -s - displays a successful creation
Parameters
- <table_name> - The name of the table you wish to make.
- [num_buckets] - The number of buckets to use as the table's capacity (If no number is specified, the default is 100)
Example
A basic usage for a hash table.
; call the setup once ; /abbr_setup ; ; //echo -a $abbr(lol) ; alias abbr_setup { ;create the table hmake abbr 1000 ; populate the table hadd abbr lol laughing out load hadd abbr omg oh my gosh hadd abbr lmao laughing my a?? off hadd abbr brb be right back ; ... } ; get the abbreviation alias abbr return $hget(abbr, $1)
Because a hash table of 1 buck is the same as a linked list, we can easily implement an almost-native stack data structure.
;/stack_example ; Output: ; poped: DDD ; poped: CCC ; poped: BBB ; poped: AAA alias stack_example { ; create a linked-list hmake stack 1 ; push items push stack AAA push stack BBB push stack CCC push stack DDD ; pop everything while ($pop(stack)) { echo -a poped: $v1 } ; delete linked-list hfree stack } alias push { ; keep a counter so we keep a unique key each time if (!$hget($1,0).item) hadd $1 counter 1 else hadd $1 counter $calc($hget($1, counter).data + 1) ; make it the first item hadd $1 key. $+ $hget($1, counter).data $2 } alias pop { if ($hget($1, 1).item != counter && $hget($1, 1).data) { ; delete the item hdel $1 $hget($1, 1).item ; return value return $v1 } }
Compatibility
Added: mIRC v5.8
Added On: 05/09/2000
Note: Individual switches were not taken into consideration.