void(
  !function(max,sizes,index,image,size,style){
    while(index--&&(size=sizes[index])>max); // choose largest QR code that will fit
    style=image.style, style.position="fixed",
    style.zIndex=-1>>>1, // ensure top z-index :)
    style.top=style.left="50%", style.marginTop=style.marginLeft=size/-2+"px", // center image on viewport
    image.src="http://chart.apis.google.com/chart?cht=qr&chld=H|0&chs="+size+"x"+size+"&chl="+escape(location) // load QR code via Google's Chart API
  }(
    Math.min(top.innerHeight,top.innerWidth), // max: maximum available viewing area
    [100,150,200,250,300,350,400,500], // sizes: optional QR code sizes
    8, // index: initial array pointer
    document.body.appendChild(new Image) // image: append image to page
  )
)