Speed Difference?

[jckl]

Is there enough speed difference to notice in a loop between .while and using jumps.. For example if you had the fillowing would one be faster or better to use?

Code Select Expand


     .while (eax < Len)
       mov byte ptr [ebx+eax], '0'
       inc eax
     .endw


Code Select Expand


       @@:
       cmp eax, Len
       jge @F
       mov byte ptr [ebx+eax], '0'
       inc eax
       jmp @B
       @@:


[hutch--]

There is a simple solution to this question, just test both and see which one is faster. On a wider scale, if its truly speed critical code, you may be able to do it faster than either alternative here, it looks like a zero fill algo so it can probably be hurried up a lot.

[jckl]

what about in general.. would jumps perform faster than while loops or if statements?

[hutch--]

This is what the loop code disassembles to.

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    jmp lbl1

  lbl0:
    mov BYTE PTR [eax+ebx], 30h
    inc eax

  lbl1:
    cmp eax, [ebp-4]
    jb lbl0


The manual code is no faster but there are tricks like unrolling or if its safe, doing DWORD writes on the buffer.

[jckl]

ok thx... one otherquestion i have is if insert 4000 items into a listview using a loop the listview seems to take a few seconds to display. Is there a way to speed that up so it dont take the extra time to display the results?

[hutch--]

One trick is to turn off the display update while you are loading the listview.

Code Select Expand


    invoke SendMessage,hWin,WM_SETREDRAW,FALSE,0

  ; load the list

    invoke SendMessage,hWin,WM_SETREDRAW,TRUE,0


[jckl]

awww that did the trick i was looking for.. Thanks again  :toothy

[donkey]

Hi jckl,

Another way to speed up adding items to a listview is to tell it how many items you will be adding in advance, that way it is not constantly allocating memory for the new items, this is done using the LVM_SETITEMCOUNT message. I have found that for listviews with large amounts of data it can help alot. If you have extremely large numbers of items it is always best to use a Virtual ListView and that way it will appear instantly as your program is responsible for providing the data and the ListView does not need to store the data. Virtual ListViews are created using the LVS_OWNERDATA style. You can see an example of a Virtual ListView in the hex viewer of WinExplorer.