Javascript TypedArray performance

Question

Why are TypedArrays not faster then usual arrays? I want to use precalc values for CLZ(compute leading zeros function). And i don\'t want they interpreting as usual objects?

Answer 1

var buffer = new ArrayBuffer(0x10000);
var Uint32 = new Uint32Array(buffer);

is not the same thing as:

var Uint32 = new Uint32Array(0x10000);

not because of the new ArrayBuffer (you always get an array buffer: see Uint32.buffer in both cases) but because of the length parameter: with ArrayBuffer you have 1 byte per element, with Uint32Array you have 4 bytes per element.

So, in the first case (and in your code), Uint32.length = 0x1000/4 and your loops are out of bounds 3 out of 4 times. But sadly you will never get errors, only poor performances.

Using 'new ArrayBuffer', you have to declare Uint32 like this:

var buffer = new ArrayBuffer(0x10000 * 4);
var Uint32 = new Uint32Array(buffer);

See jsperf with (0x10000) and jsperf with (0x10000 * 4).