Created
October 15, 2010 17:32
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// http://en.wikipedia.org/wiki/Fast_inverse_square_root | |
/* | |
Discovering old well known algorithm speed in js. | |
*/ | |
var _invSqrtL = (function() | |
{ | |
var u32Array = new Uint32Array(1), f32Array = new Float32Array(u32Array.buffer); | |
return function(x) | |
{ | |
f32Array[0] = x; | |
u32Array[0] = 0x5f3759df - (u32Array[0] >> 1); | |
var y = f32Array[0]; | |
return y * (1.5 - 0.5 * x * y * y); | |
}; | |
})(); | |
_speedTest( | |
[ | |
function(n) | |
{ | |
// _invSqrtL inlined manualy | |
var u32Array = new Uint32Array(1), f32Array = new Float32Array(u32Array.buffer); | |
var s = 0; | |
var i = n; while(i--) | |
{ | |
f32Array[0] = i; | |
u32Array[0] = 0x5f3759df - (u32Array[0] >> 1); | |
var y = f32Array[0]; | |
s += y * (1.5 - 0.5 * i * y * y); | |
} | |
}, | |
function(n) | |
{ | |
var _sqrt = Math.sqrt; // caching for best speed | |
var s = 0; | |
var i = n; while(i--) | |
{ | |
s += 1/_sqrt(i); | |
} | |
} | |
], | |
10000 | |
); | |
/* | |
chrome8 | |
0: 820 ms | |
1: 411 ms | |
ff4 | |
0: 132 ms | |
1: 284 ms | |
*/ | |
/* | |
Yes it faster in js too, but only in one browser and requires special api. | |
Anyway nice. | |
*/ |
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