base64にエンコードする

<script>a="abcdefghijklmnopqrstuvwxyz";c=a.toUpperCase()+a+"0123456789+/";
onload=function(){document.write(e(prompt("","")));}
function f(b){return c.charAt(b);}function e(k){r="";i=0;l=k.length;while(i<l){
x=k.charCodeAt(i++) & 0xff;if(i==l){r+=f(x>>2);r+=f((x&0x3)<<4);r += "==";
break;}y=k.charCodeAt(i++);if(i==l){r+=f(x>>2);r+=f(((x&0x3)<<4) | ((y&0xF0)>>4));
r+=f((y&0xF)<<2);r+="=";break;}z=k.charCodeAt(i++);r+=f(x>>2);
r+=f(((x&0x3)<<4 | (y&0xF0)>>4) >> 4);r+=f(((y&0xF)<<2) | ((z&0xC0)>>6));
r+=f(z&0x3F);}return r;}</script>

１行減らせる？