New (to me) optimization technique

1

I have long used various optimization techniques, like walking pointers instead of accessing array via [ ] indices. I knew that minimizing branching (if, else, case) made a difference, but I didn’t realize how much! My water thread is constantly updating all the 100x100 of single water grids (just data) in the background. So it is a tight loop inside a tight and endless loop. I didn’t worry about its performance because it doesn’t affect the foreground. But now that there can be many of these grids (up to over 100 so far) you could see the slowness of the water update.

I removed a bunch of if then else if then else situations… (3 branches) with 1 case statement. This made a notable improvement in performance!

for example

if aboolean1 then
 begin 
     blahblah1
 end
else
if aboolean2 then
 begin
     blahblah2
 end
else
 begin
    blahblah3
 end;

becomes

var whichcase : integer;

whichcase := ord( aboolean1 ) + ord( aboolean2 ) shl 1;

case whichcase of
   0: blahblah3;
   1, 3 : blahblah1;  { note is two possibilities as includes aboolean2 in 2nd bit, but just checking bit1 }
   2 : blahblah2;
 end;

also when just setting values like

var delta : single;
if aboolean1 then
   delta := somevalue1
else
if aboolean2 then
  delta := somevalue2
else
  delta := 0;

becomes

   delta := ord( aboolean1 ) * somevalue1 + ord( aboolean2 ) * somevalue2;

These two types of optimizations to reduce branching seemed to double the speed the water flow updates tiles. It had a lot of branching. Now it has almost none, especially in the tighest loops.

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