221: Random Number

Explain xkcd: It's 'cause you're dumb.
Jump to: navigation, search
Random Number
RFC 1149.5 specifies 4 as the standard IEEE-vetted random number.
Title text: RFC 1149.5 specifies 4 as the standard IEEE-vetted random number.

[edit] Explanation

The comic specifies a function (in a C-like syntax), which should return a random number. Most functions of this form are random number generators, implying that they return on subsequent calls different numbers. But the programmer has instead created a function that just returns always the same random number; random, because it was chosen by rolling a die as the comment documented. This function is essentially worthless, as it could simply be replaced by a "4" wherever it is used. And in fact, most modern compilers would do this automatically.

The IEEE is the organization responsible for maintaining a number of computer standards. An RFC, or Request for Comments, is a formal document put out to computing experts by IETF in the hopes of becoming a future standard. However, RFC 1149 was an April Fools' joke, defining how carrier pigeons can be used to transmit Internet packets. The RFC 1149.5 simply does not exist.

[edit] Transcript

int getRandomNumber()
{
    return 4;     // chosen by fair dice roll.
                  // guaranteed to be random.
}

[edit] Trivia

The comic also has a philosophical bent, by showcasing the limits of knowledge for an external observer. Someone who is calling this function, but unable to see its source code, will never be able to tell with 100% confidence whether the function is flawed. Even if she runs the function 10 times, and it always returns 4, there is always the possibility that it could be a fluke. As she runs the function more and more times, she can develop more confidence in the theory that the function is faulty. But unless she breaks the barrier and examines the source code itself, she will never be able to declare the function to be faulty with 100% confidence.

Despite the extreme example given, this is actually a practical problem which likely exists in the real world. If the function was more sophisticated but still had a 5% bias towards one number under certain circumstances, this would be extremely hard to notice & prove. More likely, the API users would continue to believe that the RNG is working as intended, without realizing the flaw inherent in it; anyone who grumbles about seeing 4 very frequently may even be accused of not understanding the non-uniform nature of randomness. Given the extremely large number of APIs & libraries present, and that not all of them are fully examined & understood by 3rd party experts, such flaws are likely present in our world as well. These flaws may even have been purposely introduced by a malicious agent or entity seeking to exploit them.

Comment.png add a comment!

Discussion

The syntax looks like perfectly valid java to me.213.64.1.189 22:00, 11 March 2013 (UTC)

Looks like Java to me too. 139.216.242.254 (talk) (please sign your comments with ~~~~)

How can Java come to mind when it is pure C syntax, which predates Java by several years and is arguably better known. A feature of most languages is that they have a "C-like syntax". See, a whole page on Wikipedia - http://en.wikipedia.org/wiki/List_of_C-based_programming_languages 122.161.20.238 19:53, 22 August 2013 (UTC)
"C-like syntax" is the best explain, this covers all. Even when I disagree that it's better known than Java these days.--Dgbrt (talk) 21:04, 22 August 2013 (UTC)
Just to be particularly pedantic, the double slash for the comment (which is generally utilised in object oriented C-style languages) should be avoided in C to retain backwards compatibility with C89, although it's a valid construct in C99. I'd offer, too, that the lack of library inclusion suggests this isn't necessarily Java, though it's been a couple years since I've had the opportunity to code in it. Thokling (talk) 15:35, 20 September 2013 (UTC)

As a proof of good joke, RFC 1149 was successfully implemented several times. -- Hkmaly (talk) 08:55, 11 May 2013 (UTC)

Actually, a poor “random” function like “return 4;” would be quickly determined by statistical test tools (Diehard, Dieharder, etc.) to generate very poor random number. Samiam (talk) 19:55, 28 October 2013 (UTC)

The number is random, I'm sure Randall really did this "fair dice roll". And even the name of the function is correct, it just returns a random number. A programmer would expect a random number generator, but Randall can't roll the dice all the time.--Dgbrt (talk) 21:37, 28 October 2013 (UTC)
<<sound of crickets chirping>> 108.162.219.58 02:24, 6 February 2014 (UTC)
Personal tools
Namespaces

Variants
Actions
Navigation
Toolbox

It seems you are using noscript, which is stopping our project wonderful ads from working. Explain xkcd uses ads to pay for bandwidth, and we manually approve all our advertisers, and our ads are restricted to unobtrusive images and slow animated GIFs. If you found this site helpful, please consider whitelisting us.

Want to advertise with us, or donate to us with Paypal or Bitcoin?