Fibonacci

annotated.js

/**
 * A tweet-sized, Fibonacci sequence generator.
 * 
 * @param {number} n index within the sequence
 * @return {number} Fibonacci value corresponding to the index 
 */
function(n) {
    for (var a = 0, b = 1, i = 2; i <= n;) {
        (i++ % 2) ? b += a : a += b;
    }

    return (n % 2) ? b : a;
}

index.js

function(n){for(var a=0,b=1,i=2;i<=n;)i++%2?b+=a:a+=b;return n%2?b:a}

LICENSE.txt

Copyright (c) 2011 Stephen M. McKamey, http://mck.me
 
Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:
 
The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.
 
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

package.json

{
  "name": "fib_tweet",
  "description": "A tweet-sized, Fibonacci sequence generator.",
  "keywords": [
    "Fibonacci",
    "fib",
    "tweet"
  ]
}

Shorter (73 bytes vs. original 85 bytes):

function(n,a,b,i){a=0,b=1,i=2;while(i<=n)i++%2?b+=a:a+=b;return(n%2)?b:a}

Maybe we can add extra features!

Google Closure Compiler compacts even smaller (69 bytes)!

function(n){for(var a=0,b=1,i=2;i<=n;)i++%2?b+=a:a+=b;return n%2?b:a}

Perhaps the other half should be used for unit tests. :)

62 bytes!

function(n,a,b){for(a=n&1,b=1-a;n>0;--n&1?b+=a:a+=b);return a}

Very nice! You can even move to a normal "var " statement since the args hack (",a,b") is the same length of 4 chars:

function(n){for(var a=n&1,b=1-a;n>0;--n&1?b+=a:a+=b);return a}

I guess you deliberately avoided doing it this way, but smaller for the same functionality anyway; 41b:

function f(n){return n>1?f(n-1)+f(n-2):n}

@wrayal - I would argue that the recursive implementation isn't the same functionality. Try f(50) in both implementations and you'll see what I mean.

@wrayal: Also your recursive version pollutes the global namespace which is against the 3rd rule of 140byt.es. The 140byt.es "valid" recursive implementation of the Fibonacci function takes 62 bytes too:

function(){return function F(n){return n<2?n:F(n-1)+F(n-2)}}()

But of course the recursive approach will most likely throw some stack overflow or other OOM errors.

Did you guys see the 52bytes Fibonacci ? https://gist.github.com/986590

@mckamey: Hence my statement "I guess you deliberately avoided doing it this way...". However, I would contend that functionality is intrinstically context dependent: here the context is to the shortest code that works. My pollution of the global namespace is not so OK though I guess! ^_^

@p01: Long time no speak! I figured it wasn't such a crime since the same manner of pollution has even been used in some of Jed's codes without being flagged; the original script I had written down was the same code you gave but I couldn't see another way to knock out a spare byte, nor did I notice the 52byte version (thanks for the link!). I take your point about OOM errors though; this is a more significant functional difference =)

@wrayal: Indeed. Crazy busy. o_O Do you have a link to one of Jed's 140byt.es gists using a named function?

@p01: I thought I had a better example where it wasn't picked up in the comments, but the only one I could see immediately was this: https://gist.github.com/962814

Thanks for sharing. The argument is sound. I relayed it to the master/parent gist.