Math.clz()

Jussi Kalliokoski jussi.kalliokoski at gmail.com
Tue Feb 28 09:31:32 PST 2012


We're working on JS audio decoders, and one huge performance issue atm is
clz() [count leading zeroes], which is a very commonly used algorithm in
decoders. We've tried several different approaches and benchmarked them
[1], however, different approaches work better on different engines, so
optimizing the function is a bit of a no-go, especially if we want to have
it fast in the future as well.

So, I thought I'd propose something that would go well with the earlier
proposals to extend Math [2]:

Math.clz(number)

This would allow for great speed boost in our decoders if it the JS engine
had this built-in and optimized.

While at it, it might be wise to add other related functions as well, such
as clo (count leading ones), although not as useful.

Cheers,
Jussi

[1]: http://jsperf.com/read-leading-zeros/8
[2]: http://wiki.ecmascript.org/doku.php?id=harmony:more_math_functions
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