Server : Apache/2.4.6 (CentOS) OpenSSL/1.0.2k-fips PHP/7.4.20 System : Linux st2.domain.com 3.10.0-1127.10.1.el7.x86_64 #1 SMP Wed Jun 3 14:28:03 UTC 2020 x86_64 User : apache ( 48) PHP Version : 7.4.20 Disable Function : NONE Directory : /var/www/html/netphim/layout/default/node_modules/hls.js/src/utils/ |
/*
* compute an Exponential Weighted moving average
* - https://en.wikipedia.org/wiki/Moving_average#Exponential_moving_average
* - heavily inspired from shaka-player
*/
class EWMA {
public readonly halfLife: number;
private alpha_: number;
private estimate_: number;
private totalWeight_: number;
// About half of the estimated value will be from the last |halfLife| samples by weight.
constructor(halfLife: number, estimate: number = 0, weight: number = 0) {
this.halfLife = halfLife;
// Larger values of alpha expire historical data more slowly.
this.alpha_ = halfLife ? Math.exp(Math.log(0.5) / halfLife) : 0;
this.estimate_ = estimate;
this.totalWeight_ = weight;
}
sample(weight: number, value: number) {
const adjAlpha = Math.pow(this.alpha_, weight);
this.estimate_ = value * (1 - adjAlpha) + adjAlpha * this.estimate_;
this.totalWeight_ += weight;
}
getTotalWeight(): number {
return this.totalWeight_;
}
getEstimate(): number {
if (this.alpha_) {
const zeroFactor = 1 - Math.pow(this.alpha_, this.totalWeight_);
if (zeroFactor) {
return this.estimate_ / zeroFactor;
}
}
return this.estimate_;
}
}
export default EWMA;