What type of loops do you use?

[espruino-discuss]

Posted at 2020-07-31 by @MaBecker

There has been a lot talking about loop performance.

So lets's try to find out if there is a difference between loops and loops.

Tested on an original Espruino board so others may differ for the time but not for the result.

VERSION: "2v05",
GIT_COMMIT: "990dac35",
BOARD: "PICO_R1_3",

Test code snipped with for, while and do.

var LOOPS = 1E4;

function forLoop(){
      for (i = 0; i < LOOPS; i++) {
          x = 0;
      }
}

function whileLoop(){
      var i = LOOPS;
      while (i) {
           i--;
      }
}

function doLoop(){
      var i = LOOPS;
      do {
           i--;
      } while(i);
}

function run(f){
      ts = getTime();
      f();
      te = getTime();
      return te - ts;
}

testing:

// result time is in seconds
>run(forLoop) 
=2.67205524444

>run(whileLoop);
=1.25568199157 

>run(doLoop);
=1.31462860107

As a result: Try to use do or while loops instead of for loops , they run nearly twice as long.

[gfwilliams]

Posted at 2020-07-31 by @gfwilliams

It's not an entirely fair comparison if you've got x=0 in the for loop but not in any other loops, but I believe for will be slower anyway, just because Espruino is having to jump between 3 different places (the loop iterator, condition and body)...

The fastest would be:

      var i = LOOPS;
      while (i--) {
      }

[espruino-discuss]

Posted at 2020-07-31 by @MaBecker

Well not sure about this, isn't x=0 faster than `i++, but let's compare the empty loops.

function forLoopV2(){
      for (i = 0; i < LOOPS; i++) {}
}

function whileLoopV2(){
      var i = LOOPS;
      while (i--) {}
} 

>run(forLoopV2)
=1.96909236907
>run(whileLoopV2)
=0.91626548767

Any way it is clear that while loops are faster than for loops.