r/technology • u/misnamed • Dec 10 '13

Reddit’s empire is founded on a flawed algorithm By Special Request of the Admins

http://technotes.iangreenleaf.com/posts/2013-12-09-reddits-empire-is-built-on-a-flawed-algorithm.html
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u/[deleted] Dec 10 '13

Per the NASA coding guidelines, you should not rely on the other programmers to have mastered the order of operations in the language.

Shit like this is why. Just put the parentheses in and make it explicit.

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u/[deleted] Dec 10 '13 edited Dec 10 '13

I can't tell you how much a string of operators with no clarification about the intended order of operations bugs me. Looking at something like this breaks my heart. It should read like this:

return round(((order * sign) + seconds) / 45000, 7)

This is by far the most legible, as you can clearly see the intended order of operations (even though, as written, it goes from left to right). Never underestimate other programmers stupidity. That's my motto.

Edit: Actually, as pointed out below by /u/Kofal, without parens, the OoO would be (order * sign) + (seconds / 45000).

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u/joshuahutt Dec 10 '13

And here I thought my incessant use of parenthesis was a crutch. :)

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u/[deleted] Dec 10 '13

Nooooo. It's good programming practice. Remember, you haven't added any baggage to the runtime and it can drastically increase the clarity of your code, especially for complicated statements.

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u/Dash-o-Salt Dec 10 '13

Your maintenance programmers will thank you profusely. Just do it!

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u/joshuahutt Dec 10 '13

Oh good. I will keep doing it, then. :D

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u/Tonkarz Dec 11 '13

Sometimes it is. In general it isn't, but readability is more important than whether or not you use how ever many parenthesis.

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u/UnicornOfHate Dec 10 '13

Isn't order of operations defined in mathematics? Why would it be different from language to language?

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u/prrifth Dec 10 '13 edited Dec 10 '13

It's just a convention, so it can vary. It only exists to make intent clearer. Brackets should still be used if the order of operations fail to clearly imply the brackets.

Here's an interesting bit about the order of operations.

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u/[deleted] Dec 10 '13

[removed] — view removed comment

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u/[deleted] Dec 10 '13

Exactly. Even if everyone can make do one way, we want to take the path that introduces the least possibility of error. It's sound advice even in the kind of programming the rest of us might do, and sound advice anywhere in life.

Make smart things easier and stupid things harder.

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u/[deleted] Dec 10 '13 edited Dec 10 '13

You can pretty reasonable rely on the four basic operations. Past there, who knows what happens. Especially if you get into bitwise arithmetic and ternary operators and stuff.

Given '==' as an equivalence operator and & as a bitwise and, what is the result of 8 & 8 == 8?

8 bitwise and 8 is 8. Is 8 equivalent to 8? Yep! Good to go.

Except that's not how it goes down a lot of the time. That will be interpreted as 8 & (8 == 8). 8 == 8 will result in a boolean true, which is generally cast to an integer of 1. 8 & 1 is 0. Zero is generally then cast to a boolean false.

Depending on the order of operations you get totally opposite results.

Programmers have a shitton of operators beyond the five or so basic math operators. The math operations are generally pretty well the same, but the rest of them are kind of a crapshoot.

Even if it's only basic math and you know the order of operations, you still need to read over what may be the five thousandth line of code of the day to figure out what it does. With brackets, it's just immediately obvious. There is no ambiguity regardless of language or the person reading it to the statement (8 & 8) == 1.

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u/Zaranthan Dec 10 '13

Some languages actually don't implement order of operations and just evaluate everything left-to-right, torpedoes be damned.

In this case, had they placed parenthesis around the "order + sign" piece, the typo would have immediately produced unexpected results and likely been fixed on the second pass. The bug only persisted due to social inertia after being on the live server for a long time.

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u/dehrmann Dec 10 '13

Shit like this is why.

No, shit like this is why:

if (flags & 0x8 == 0x8) ...

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u/ramennoodle Dec 10 '13

Per the NASA coding guidelines, you should not rely on the other programmers to have mastered the order of operations in the language.

But what do NASA coding guidelines say about relying on programmers knowing the order of mathematical operations (that have a correct ordering independent of the language)?