How is SSL calculated?

anyone knows how SSL indicator is calculated?

thanks

for(int i=Bars-Lb;i>=0;i--)
{
if(Close[i]>iMA(Symbol(),0,Lb,0,MODE_SMA,PRICE_HIGH,i+1))
Hld=1;
else
{
if(Close[i]<iMA(Symbol(),0,Lb,0,MODE_SMA,PRICE_LOW,i+1))
Hld=-1;
else
Hld=0;
}
if(Hld!=0)
Hlv=Hld;
if(Hlv==-1)
ssl[i]=iMA(Symbol(),0,Lb,0,MODE_SMA,PRICE_HIGH,i+1);
else
ssl[i]=iMA(Symbol(),0,Lb,0,MODE_SMA,PRICE_LOW,i+1);
}