The speed of MC

[wouter]

> The speed of MC
>
>     * From: Wil Dijkstra
>     * Subject: The speed of MC
> * Date: Mon, 31 Mar 2003 08:17:21 -0800
>
> How to speed up MC

----- snip   :^))

> To write scripts that executes as fast as possible, you should know
> something about how a computer (or MetaCard) works, how data are 
> stored,
> etc. I’m going to tell you that in a very, very simplified way. But
> first, the fast script:
>
> script B
>
>   repeat with i = 1 to 10000
>     put random (1000) & cr after randList
>   end repeat
>   delete last char of theList
>
> Script B yields exactly the same result as script A, but is more then
> ten times as fast. If we wanted to generate random numbers between 1 
> and
> 1000000, it is even more then 20 times as fast.
>
------- snip


Very nice indeed.
And if you are really into the need for speed, script B is even a tad 
faster  like this :

script B

   repeat 10000
     put random (1000) & cr after randList
   end repeat
   delete last char of randList

Another speed improvement on repeat loops may be obtained in certain 
cases (depending on the massiveness of the number of repeats and on the 
amount and kind of data processed), by using the old technique of 
"unrolling" the repeat loop (which also works on script languages).
Instead of a lengthy explanation on the overhead of the repeat loop 
itself, let the the following be self-explanatory. Feed x some numbers :

on mouseUp
   put fld "orig" into x
   put "calculating....." into fld "result"
   put "" into theResult
   put 0 into a
   put 0 into b
   put 0 into c
   put the long seconds into Time1
   repeat 10000
     add (x + x + x + x + x + x + x + x + x + x)  to a
   end repeat
   put the long seconds into Time2
   repeat with i = 1 to 10000
     add (x + x + x + x + x + x + x + x + x + x)  to b
   end repeat
   put the long seconds into Time3
   repeat 500
     add (x + x + x + x + x + x + x + x + x + x)  to c
     add (x + x + x + x + x + x + x + x + x + x)  to c
     add (x + x + x + x + x + x + x + x + x + x)  to c
     add (x + x + x + x + x + x + x + x + x + x)  to c
     add (x + x + x + x + x + x + x + x + x + x)  to c
     add (x + x + x + x + x + x + x + x + x + x)  to c
     add (x + x + x + x + x + x + x + x + x + x)  to c
     add (x + x + x + x + x + x + x + x + x + x)  to c
     add (x + x + x + x + x + x + x + x + x + x)  to c
     add (x + x + x + x + x + x + x + x + x + x)  to c
     add (x + x + x + x + x + x + x + x + x + x)  to c
     add (x + x + x + x + x + x + x + x + x + x)  to c
     add (x + x + x + x + x + x + x + x + x + x)  to c
     add (x + x + x + x + x + x + x + x + x + x)  to c
     add (x + x + x + x + x + x + x + x + x + x)  to c
     add (x + x + x + x + x + x + x + x + x + x)  to c
     add (x + x + x + x + x + x + x + x + x + x)  to c
     add (x + x + x + x + x + x + x + x + x + x)  to c
     add (x + x + x + x + x + x + x + x + x + x)  to c
     add (x + x + x + x + x + x + x + x + x + x)  to c
   end repeat
   put the long seconds into Time4
   put "• add (x + x + x + x + x + x + x + x + x +x) to xx"   & cr after 
theResult
   put " --> " &  (a + b + c) / 3 & cr after theResult
   put Time2 - Time1 & " --> repeat 10000 times" &  cr  after theResult
   put Time3 - Time2 & " --> repeat with i = 1 to 10000 times" &  cr 
after theResult
   put Time4 - Time3 & " --> repeat unrolled to 500 times"  & cr  after 
theResult
   put "" into a
   put "" into b
   put "" into c
   put the long seconds into Time1
   repeat 100000
     add x to a
   end repeat
   put the long seconds into Time2
   repeat with i = 1 to 100000
     add x to b
   end repeat
   put the long seconds into Time3
   repeat 5000
     add x to c
     add x to c
     add x to c
     add x to c
     add x to c
     add x to c
     add x to c
     add x to c
     add x to c
     add x to c
     add x to c
     add x to c
     add x to c
     add x to c
     add x to c
     add x to c
     add x to c
     add x to c
     add x to c
     add x to c
   end repeat
   put the long seconds into Time4
   put "• add x to xx" & cr after theResult
   put " --> " &  (a + b + c) / 3 & cr after theResult
   put Time2 - Time1 & " --> repeat 100000 times" &  cr  after theResult
   put Time3 - Time2 & " --> repeat with i = 1 to 100000" &  cr after 
theResult
   put Time4 - Time3 & " --> repeat unrolled to 5000 times"  after 
theResult
   put theResult into fld "result"
end mouseUp


While you are at it, you can try the difference in speed in massive 
repeat loops  between:
add x to a
and
put a + x into a

For those who like copy - pasting :

on mouseUp
   put fld "orig" into x
   put "calculating....." into fld "result"
   put "" into theResult
   put 0 into a
   put 0 into b
   put 0 into c
   put the long seconds into Time1
   repeat 10000
     put  a + (x + x + x + x + x + x + x + x + x + x)  into a
   end repeat
   put the long seconds into Time2
   repeat with i = 1 to 10000
     put  b + (x + x + x + x + x + x + x + x + x + x)  into b
   end repeat
   put the long seconds into Time3
   repeat 500
     put c + (x + x + x + x + x + x + x + x + x + x)  into c
     put c + (x + x + x + x + x + x + x + x + x + x)  into c
     put c + (x + x + x + x + x + x + x + x + x + x)  into c
     put c + (x + x + x + x + x + x + x + x + x + x)  into c
     put c + (x + x + x + x + x + x + x + x + x + x)  into c
     put c + (x + x + x + x + x + x + x + x + x + x)  into c
     put c + (x + x + x + x + x + x + x + x + x + x)  into c
     put c + (x + x + x + x + x + x + x + x + x + x)  into c
     put c + (x + x + x + x + x + x + x + x + x + x)  into c
     put c + (x + x + x + x + x + x + x + x + x + x)  into c
     put c + (x + x + x + x + x + x + x + x + x + x)  into c
     put c + (x + x + x + x + x + x + x + x + x + x)  into c
     put c + (x + x + x + x + x + x + x + x + x + x)  into c
     put c + (x + x + x + x + x + x + x + x + x + x)  into c
     put c + (x + x + x + x + x + x + x + x + x + x)  into c
     put c + (x + x + x + x + x + x + x + x + x + x)  into c
     put c + (x + x + x + x + x + x + x + x + x + x)  into c
     put c + (x + x + x + x + x + x + x + x + x + x)  into c
     put c + (x + x + x + x + x + x + x + x + x + x)  into c
     put c + (x + x + x + x + x + x + x + x + x + x)  into c
   end repeat
   put the long seconds into Time4
   put "• put xx + (x + x + x + x + x + x + x + x + x +x) into xx"   & 
cr into theResult
   put " --> " &  (a + b + c) / 3 & cr after theResult
   put Time2 - Time1 & " --> repeat 10000 times" &  cr after theResult
   put Time3 - Time2 & " --> repeat with i = 1 to 10000 times" &  cr 
after theResult
   put Time4 - Time3 & " --> repeat unrolled to 500 times"  & cr  after 
theResult
   put 0 into a
   put 0 into b
   put 0 into c
   put the long seconds into Time1
   repeat 100000
     put  a + x into a
   end repeat
   put the long seconds into Time2
   repeat with i = 1 to 100000
     put  b + x into b
   end repeat
   put the long seconds into Time3
   repeat 5000
     put  c + x into c
     put  c + x into c
     put  c + x into c
     put  c + x into c
     put  c + x into c
     put  c + x into c
     put  c + x into c
     put  c + x into c
     put  c + x into c
     put  c + x into c
     put  c + x into c
     put  c + x into c
     put  c + x into c
     put  c + x into c
     put  c + x into c
     put  c + x into c
     put  c + x into c
     put  c + x into c
     put  c + x into c
     put  c + x into c
   end repeat
   put the long seconds into Time4
   put "• put xx + x into xx" & cr after theResult
   put " --> " &  (a + b + c) / 3 & cr after theResult
   put Time2 - Time1 & " --> repeat 100000 times" &  cr  after theResult
   put Time3 - Time2 & " --> repeat with i = 1 to 100000" &  cr after 
theResult
   put Time4 - Time3 & " --> repeat unrolled to 5000 times"  after 
theResult
   put theResult into fld "result"
end mouseUp

Have a nice whatever.
WA