mirror of
https://github.com/jellyfin/jellyfin-web
synced 2025-03-30 19:56:21 +00:00
38 lines
968 B
JavaScript
38 lines
968 B
JavaScript
|
/*
|
||
|
|
* compute an Exponential Weighted moving average
|
||
|
|
* - https://en.wikipedia.org/wiki/Moving_average#Exponential_moving_average
|
||
|
|
* - heavily inspired from shaka-player
|
||
|
|
*/
|
||
|
|
|
||
|
|
class EWMA {
|
||
|
|
|
||
|
|
// About half of the estimated value will be from the last |halfLife| samples by weight.
|
||
|
|
constructor(halfLife) {
|
||
|
|
// Larger values of alpha expire historical data more slowly.
|
||
|
|
this.alpha_ = halfLife ? Math.exp(Math.log(0.5) / halfLife) : 0;
|
||
|
|
this.estimate_ = 0;
|
||
|
|
this.totalWeight_ = 0;
|
||
|
|
}
|
||
|
|
|
||
|
|
sample(weight,value) {
|
||
|
|
var adjAlpha = Math.pow(this.alpha_, weight);
|
||
|
|
this.estimate_ = value * (1 - adjAlpha) + adjAlpha * this.estimate_;
|
||
|
|
this.totalWeight_ += weight;
|
||
|
|
}
|
||
|
|
|
||
|
|
getTotalWeight() {
|
||
|
|
return this.totalWeight_;
|
||
|
|
}
|
||
|
|
|
||
|
|
getEstimate() {
|
||
|
|
if (this.alpha_) {
|
||
|
|
var zeroFactor = 1 - Math.pow(this.alpha_, this.totalWeight_);
|
||
|
|
return this.estimate_ / zeroFactor;
|
||
|
|
} else {
|
||
|
|
return this.estimate_;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
export default EWMA;
|