do the parantheses matter?

Question

Given this JSPerf test

Why is this faster

var x;var i = 1E4;var j = 1E4;
for (; i-- > -1;) {
  x = -~x;
}
for (; j-- > -1;) {
  x = ~ - x;
}

Than this ?

var x;var i = 1E4;var j = 1E4;
for (; j-- > -1;) {
  x = -1 * ~x;
}
for (; j-- > -1;) {
  x = ~ (-1 * x);
}

Is the second version better optimizable, or what is the reason?

Are you resetting `j` somewhere in the second example? – imreal Jun 20 '13 at 20:35 — imreal, Jun 20 '13 at 20:35

score 1 · Answer 1 · answered Jun 20 '13 at 20:41

1

I believe that in the second test you are either forgetting to reset j to 1E4, or you meant to use an i in one of the loops. See this test:

I added a snippet using i in the first loop and j in the second and it performs just as fast as the first test.

answered Jun 20 '13 at 20:41

imreal

Thanks! :) Dang how could I miss that :P – Moritz Roessler Jun 20 '13 at 20:49
I'll accept his answer as it is his first answer and only a little bit later – Moritz Roessler Jun 20 '13 at 21:05

score 1 · Accepted Answer · answered Jun 20 '13 at 20:42

1

In the second code sample, you use j as the iterator in both loops.

answered Jun 20 '13 at 20:42

osbomb

2 Answers2