Script speed and #LPC

“Is goto faster than gosub?” comes up often. The answer lies in how EasyUO runs a script.

Cycles

A script runs in cycles. In each cycle it runs #LPC lines (10 by default) and then pauses 50 ms, which leaves the computer to the UO client and everything else. That makes about 20 cycles, or 200 lines, a second.

; what EasyUO does, in pseudo-code
start:
  run #LPC lines of the script
  pause 50 ms
goto start

A comment, a goto and a gosub each count as one line. Running a line takes almost no time compared with the 50 ms pause, so which command a line holds hardly matters: goto is not faster than gosub, and removing comments only saves lines, not real work. Some commands, such as key, click, target and wait, wait on purpose and take as long as they take.

Making scripts faster

Raise #LPC where a script does a lot of quick work, and lower it again afterwards:

set #LPC 1000
set %sum 0
for %i 1 1000            ; a lot of quick lines
  set %sum %sum + %i
set #LPC 10
display ok The sum is %sum
halt

A high #LPC lets the script take more of the computer’s time. That is fine for bursts of calculation, menu building or text work. For commands that make the client do work, such as finditem, a high value only uses more CPU without making the game respond faster.

Measuring

To compare commands, take the 50 ms pause out of the measurement by setting a very high #LPC, and time many repetitions with #SysTime:

set #LPC 100000000
set %start #SysTime
for %i 1 100000
  set %x 3
set %took #SysTime - %start
set #LPC 10
display ok 100000 sets took %took ms
halt

In the original EasyUO, a huge #LPC froze the EasyUO window until the loop ended. In EasyUO Reforged each script runs on its own thread and gives way briefly every 1024 lines, so the window stays usable and Stop still works.

Based on Cheffe’s tutorial on execution speed from the EasyUO wiki.

Based on the EasyUO wiki, edited for EasyUO Reforged. This text is available under the GNU Free Documentation License 1.2.