& (ampersand) and | (pipe) with strings

[schmon]

Hello people.

I have a question regarding ampersand and pipe. I've read some code where strings are parsed using the ampersand and pipe symbol, which as far as I understood were bitwise operators... Now I'm just confused because all the search queries just return things about && an || which I don't really care about.

So do you know where I could learn more about these:

for(a=0;a<=9;a++){
      document.write("_#"[a/3&1]);
}
//outputs: ' ___###___###___###___###___###_ ' 

for(a=0;a<=30;a++){
     document.write(a/5|0);
}
//outputs: 0000011111222223333344444555556 

So I've figured the effects but I'd like to understand them more in depth. Any literature I could read ?
edit: and the role of the brackets ('[ ]') in the first code ?

Thank you !

[Dok]

The two examples does not contain strings which are manipuled using & or |.

document.write("_#"[a/3&1]);

This is probably referencing an array which is a property in the window object. The brackets are for array (or property) indexing.

There is no strings in the second example.

[schmon]

Okay so basically what i want to know is what does "text"[arrayindex] do ? And I'm still confused as to the use of the & and |, even with numbers.

[scragar]

"123456"[3] == "4"
"123456".split('')[3] == "4"

the bold bit is just implied, I came to expect this behaviour while learning C, with it's intresting string methods :P


as for | and &, I'm unsure what they do, as far as I can assume & reacts somewhat similar to x&y = x%(y+1), although higher numbers of y appear to work quite differently...

[Dok]

"123456"[3] == "4"

Clever. I didn't know that.

& is bitwise AND. This means that 1001 & 0001 = 0001 as only the first bit is set in both numbers.

| is bitwise OR. This means that 1001 | 0001 = 1001 as the first and fourth bits are set in either number.

[mrhoo]

Google 'javascript bitwise operators'-
the Mozilla site has a good overview

One common use on the web is converting hex color codes to decimal-

toRgb= function(hex){
hex= hex.replace(/^#/,'0x');
var tem= [(hex >>16) & 255,(hex >> 8) & 255, hex & 255];
return 'rgb('+tem.join(',')+')';
}

[scragar]

& is bitwise AND. This means that 1001 & 0001 = 0001 as only the first bit is set in both numbers.

| is bitwise OR. This means that 1001 | 0001 = 1001 as the first and fourth bits are set in either number.

ah, makes much more sense than what I assumed, also explains why it all fell apart at higher values as well. I shall make a mental note of that.

[schmon]

Oh thanks for all that !

For anyone interested, here's the code I found on the web that was a tad puzzling (the bits that I posted):

<pre id=D></pre><script>A=0,B=0,D=document.getElementById('D'),b=[];
function u(){n=Math.sin(B);for(k=0;1840>k;k++)y=-10-k/80|0,o=41+(k%80
-40)*1.3/y+n|0,N=A-100.0/y,b[k]=k%80==79?"\n":".#"[o+N&1];D.innerHTML
=b.join('');A+=0.05;B+=0.03;setTimeout(u,10);}u();</script> 

copy, paste, save, open with a browser. Fun =-)

[Ultimater]

Wow nice 3D ascii text animation.
The mathematical algorithm intrigues me and I'll study it some more in the hope of an insight into equation-based graphics which I haven't touched since the TI-86 days.