Hash tables.

[Motu]

Take a look at this code - this way it's working

The remove function was buggy I belive...

Please note that I removed the hash Table parameter as well as the mutexes because I only need one table at a time and no multithreading support - lock and unlock mutex is very slow compared to entercriticalsection_() btw

Have fun with it.

Code: Select all

Procedure HT_RemoveItem(key$)
  Protected numelements, hash, index, firstinlist, lastinlist, item
  numelements=PeekL(HTid)
  If numelements
    ;Good to go! First job is to create the hash index.
    hash=HT_CreateHash(numelements-1, key$)+1
    ;hash is now between 1 and 'numelements'.
    ;First check if there is list of elements with the corresponding hash.
    index=HTid+hash*4
    firstinlist=PeekL(index)
    item = 0
    If firstinlist
        ChangeCurrentElement(_HTentries(),firstinlist)
        Repeat
          If _HTentries()\key=key$ And _HTentries()\tableid=HTid ;Key found!
            item=_HTentries()
          ElseIf _HTentries()\hash<>hash Or _HTentries()\tableid<>HTid ;Gone too far through the list.
            lastinlist = _HTentries()
            Break
          EndIf
        Until NextElement(_HTentries())=0
;        lastinlist=_HTentries()
        If item ;If there is an entry to remove.
          ;We now have 3 pointers to elements within the list; firstinlist, item, lastinlist.
          ;We need to use these to update the list accordingly.
          If item=firstinlist ;Need to alter the hash table entry to point to next item.
           ChangeCurrentElement(_HTentries(),item)
           DeleteElement(_HTentries())
           NextElement(_HTentries())
           PokeL(index, _HTentries())
           If _HTentries()\hash<>hash
            PokeL(index, 0)
           EndIf
          ElseIf item = lastinlist
           ChangeCurrentElement(_HTentries(),item)
           DeleteElement(_HTentries())
          Else
           ChangeCurrentElement(_HTentries(),item)
           DeleteElement(_HTentries())
          EndIf
          
        Else
         MessageRequester("There is no item to remove","",0)
        EndIf
    EndIf
  EndIf
EndProcedure

[Motu]

And you may want to remove the message request

[srod]

Motu, this version of hash tables is no longer supported - I now use the much enhanced OOP version which I posted. Thanks for the bug fix, but as I say this is an old hash table library which is really not very good.

As for critical sections, you do realise that Purebasic's mutex objects are in fact critical sections don't you?


**EDIT : the bug was in the line

Code: Select all

PokeL(index, PeekL(item-8))

within the HT_RemoveItem() function.

Change it to

Code: Select all

PokeL(index, PeekL(item-8)+8)