FOR/NEXT or WHILE?

BlitzMax Forums/BlitzMax Programming/FOR/NEXT or WHILE?

DH	(Posted 2005) [#1]

Writing a compiler (for scripts) and have found that FOR/NEXT loops use more (mathematically) then while/repeat loops...

Just a simple:

for x = 1 to 1000
next

Works slower than a

x=1
while x <= 1000
x=x+1
wend

Now this is in my scripting laguage where I convert everything to a pcode after tokenizing it all. Then merely execute the (x86-like) pcode.

I have tried to opimize it the best I can however keep coming to the same thing (that for/next loops are slower because they require slighly more math and line jumps).

Is this the same for most languages as well (IE blitz, VB, etc)?

Because in that case a slight optimization would be to change large loops (like updating verticies where the loop count can reach thousands) to a while/repeat rather than a for/next in some of the code I have used in the past.

any thoughts?

Dreamora

(Posted 2005) [#2]

can't tell the same

for me local is faster (36to 63in averange)



t1 = MilliSecs ()
For x = 1 To 10000000

Next

t1 = MilliSecs () - t1

t2 = MilliSecs ()

x = 1
While x < 10000001
	x :+ 1
Wend

t2 = MilliSecs () - t2
Print t1
Print t2

the funny thing: without strict it is 4 times as fast as with strict??????

tonyg

(Posted 2005) [#3]

While/wend is quicket on my system but turn debug off and the difference is a lot smaller.
I get the same slower rate with strict unless debug is turned off.

Dreamora

(Posted 2005) [#4]

ah your right in debug off both are the same speed again (12ms with strict) ... *note to my list: always test with and without debug due to strange implementation parts of BM*

rdodson41

(Posted 2005) [#5]

Debug off:
With or without Strict they are both hovering around 30.

Debug on:
With Strict both took around 1150 or so. Very strange.
Without Strict The ForNext loop took only 90 while the While loop took about 350.

Weird results...

Chris C

(Posted 2005) [#6]

with strict I should think local vars not global will be faster...