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+ | ====== Various hashtable facts and findings ====== | ||

+ | The N value (number of buckets) given in /hmake is increased with one if the given value is even, meaning all hashtables have an odd number of buckets. | ||

+ | |||

+ | The range of the N value as specified with /hmake is 1..10000, making the possible hashtable sizes all odd numbers from 1 to 10001 inclusive. | ||

+ | |||

+ | Each hashtable bucket uses exactly 4 bytes. Therefore, memory consumption for the buckets part of the hashtable (excluding storage of the hashtable name etc, and all of the items), is 4*N bytes. | ||

+ | |||

+ | Hashtable names are limited to 90 characters. | ||

+ | |||

+ | The hash function used by mIRC for hashtable items is the following piece of C code (posted on the old message boards by Khaled, saved by qwerty): | ||

+ | |||

+ | u_int r, i; | ||

+ | r = 0; | ||

+ | while (*string) { | ||

+ | i = *string; | ||

+ | r ^= i; | ||

+ | r <<= 1; | ||

+ | string++; | ||

+ | } | ||

+ | return r; | ||

+ | |||

+ | The resulting value is taken modulo N to determine which bucket to use for the given item. Note that item comparison is case insensitive: in mIRC 6.x, the input string is first converted to lowercase; in mIRC 7.x, it is first converted to uppercase. | ||

+ | |||

+ | The set of items associated with each bucket is a simple linked list; using hashtable size 1 therefore results in a linked list data structure. New items are added at the head of the list, i.e. $hget(size1hashtable,1).item will always return the last added item, if any. Changing the value of an existing item does not change its position in the linked list; deleting an item does not affect the order of the other items. |