Comments on: Inline Math.ceil()

By: Patrick Denny

Patrick Denny — Sat, 29 Oct 2011 01:39:34 +0000

Crap. Munged the code:

var value,res;
value=1.1;
(value == (res = value<< 0 ? res++: res--)); // res == 2
value=2;
(value == (res = value<< 0 ? res++: res--)); // res == 2
value=-1.1;
(value == (res = value<< 0 ? res++: res--)); // res == -1
value=-2;
(value == (res = value<< 0 ? res++: res--)); // res == -2

and results

Type    10000000 iterations
Math.ceil    75
your BW    51
my BW    21
your int()    48
my int()    19

If that didn’t work I hope you can get the gist

By: Patrick Denny

Patrick Denny — Sat, 29 Oct 2011 01:35:35 +0000

by moving the assignment inside the trinary, you can remove extraneous bitwise shifts (or int() calls) and it speeds up even more

var value,res;
value=1.1;
(value == (res = value&lt; 0 ? res++: res--)); // res == 2
value=2;
(value == (res = value&lt; 0 ? res++: res--)); // res == 2
value=-1.1;
(value == (res = value&lt; 0 ? res++: res--)); // res == -1
value=-2;
(value == (res = value&lt; 0 ? res++: res--)); // res == -2
<pre>
and results
<pre>
Type    10000000 iterations
Math.ceil    75
your BW    51
my BW    21
your int()    48
my int()    19

http://wonderfl.net/c/330S

By: jackson

jackson — Tue, 06 Oct 2009 05:18:21 +0000

Thanks for the follow up. Indeed this does fix the problem and now your solution looks just like mine except for how you do your casting. I was curious so I tried using your bitwise casts in the same test app on the same machine as I did the test in the article. Here’s what I got:

BW (positive only): 829
BW (positive and negative): 826

That’s nearly twice as slow as just using the int() cast. This seems to prove that the int() cast is, as Karl pointed out, much quicker than the bitwise trick in AS3. And as you point out, both of them blow away Math.ceil()!

By: aruban

aruban — Tue, 06 Oct 2009 04:55:42 +0000

(this test was done directly on Flash CS3, player 9 with an imac 2.16GHz C2D)

By: aruban

aruban — Tue, 06 Oct 2009 04:52:05 +0000

I wrote too quickly, that’s true that (val>>0)+1 works only if u sure that your value is a positive float.
Anyway, made the test and as Karl is mentioning, it looks like the casting is slightly faster that the bit shifting, which surprised me ! :)
——————-
res = value==(value>>0)?value:(value>>0)+1 //positive only
res = value==(value>>0)?value:(value>>0)+(value>=0?1:0); // pos&neg
——————-
Inline:
Positive only:
1.1: 2 == 2: PASS
2: 2 == 2: PASS
Positive and negative:
1.1: 2 == 2: PASS
2: 2 == 2: PASS
-1.1: -1 == -1: PASS
-2: -2 == -2: PASS
BS:
Positive only:
1.1: 2 == 2: PASS
2: 2 == 2: PASS
Positive and negative:
1.1: 2 == 2: PASS
2: 2 == 2: PASS
-1.1: -1 == -1: PASS
-2: -2 == -2: PASS

BW (positive only): 793
Inline (positive only): 758
BW (positive and negative): 778
Inline (positive and negative): 796
Math.ceil(): 7145
——————-
Both are anyway blowing away Math.ceil perf.
As far as I know, for performances, avoiding the use of Math object is part of the good practices :)

By: Karl Knocking

Karl Knocking — Mon, 05 Oct 2009 18:00:52 +0000

Maybe he found it here:
http://lab.polygonal.de/2007/05/10/bitwise-gems-fast-integer-math/

Although the site claims that the casting is faster in AS3..

By: jackson

jackson — Mon, 05 Oct 2009 16:36:18 +0000

That’s one crazy trick. Where did you find it? I tried it out for correctness:

Positive only:
    1.1: 2 == 2: PASS
    2: 3 == 2: FAIL
Positive and negative:
    1.1: 2 == 2: PASS
    2: 3 == 2: FAIL
    -1.1: 0 == -1: FAIL
    -2: -1 == -2: FAIL

It seems to round up whole numbers as though you did:

int(value)+1;

Which I suppose is what the bitwise shift is for. So I suppose if you knew that your input numbers were not whole numbers then it would be usable, but not in the general case.

By: aruban

aruban — Mon, 05 Oct 2009 14:28:35 +0000

nope. quick test on my macbook Air

Inline (positive only): 1067
Inline (positive and negative): 1067
bitwise operation (value>>0)+1: 698
Math.ceil(): 6484

By: aruban

aruban — Mon, 05 Oct 2009 14:23:57 +0000

Is that faster than (val >> 0)+1 ?

By: Ramon Fritsch

Ramon Fritsch — Mon, 05 Oct 2009 12:08:37 +0000

Congrats man, very useful tip.

I haven’t idea how much that is costs to cpu. great job.