javascript kodunu php ye çevirme

var __AM=65521; // the largest prime less than 2^16...

function cc(a){
   
var c = 1, b = 0, d, e;
    
for(e = 0; e < a.length; e++){
       
d = a.charCodeAt(e);
       
c = (c+d)%__AM;
       
b = (b+c)%__AM;
   
}
    
return b<<16|c;
};