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`three = 1` in the Linux sourcecode (2014)

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Re: `three = 1` in the Linux sourcecode (2014)

#61

Post by kubanczyk »

hyperman1 wrote: post #47
CWuestefeld wrote: post #36

Many years ago in an age of klocs and flowcharts, at a large three-letter computer company, there were iron-clad coding rules that must be obeyed, no questions allowed. In general you could see their reasoning, but such bureaucratic reasoning doesn't pay off. One example of this was that all numeric values used in a program must be factored out as symbolic constants. The reason for doing this is obvious, but it faile…

An application I touched a few weeks ago has a DB column named 'type' with values 1,2,3. So on to the source code we go: enum RecordType {TypeOne(1),TypeTwo(2),TypeThree(3); RecordType(int dbValue) ...} As it happens, I know an end user of this particular beast, so I show her some record IDs of each type and ask in what way they differ. She looks a few seconds, then says: 'This is clearly a type one record, the next…

This part looks like those people formed a neural network. They are able to learn to act quasi-intelligently, but when you peek inside, the internal model is just a bunch of numbers.

Edit: scratch that neural network. They just made one neuron so far.

Re: `three = 1` in the Linux sourcecode (2014)

#62

Post by thechao »

yiyus wrote: post #55
CWuestefeld wrote: post #36

Many years ago in an age of klocs and flowcharts, at a large three-letter computer company, there were iron-clad coding rules that must be obeyed, no questions allowed. In general you could see their reasoning, but such bureaucratic reasoning doesn't pay off. One example of this was that all numeric values used in a program must be factored out as symbolic constants. The reason for doing this is obvious, but it faile…

I would do this: #define I 1 #define II 2 #define III 3 ... #define XIII 13 There is no zero in roman numerals, but you can use NULL for extra fun! (yes, I am a bad person)

The Roman numeral for ‘0’ is (nonclassically) ‘N’; there are attestations going back to the early 6th c. It stands for “nulla” or “nihila”.

Re: `three = 1` in the Linux sourcecode (2014)

#63

Post by calibas »

hinoki wrote: post #3
post-factum wrote: post #2

705 /* 706 * Iterate through the groups which hold BACKUP superblock/GDT copies in an 707 * ext4 filesystem. The counters should be initialized to 1, 5, and 7 before 708 * calling this for the first time. In a sparse filesystem it will be the 709 * sequence of powers of 3, 5, and 7: 1, 3, 5, 7, 9, 25, 27, 49, 81, ... 710 * For a non-sparse filesystem it will be every group: 1, 2, 3, 4, ... 711 */ 712 static unsigned…

Yeah, maybe calling them pow3, pow5, pow7 would be a bit clearer? But a 10s search for a comment cleared it up, so I don’t really see the problem...

And the scope for "three" is quite small, a single short function. It's not like it's using a global variable or #define.

Re: `three = 1` in the Linux sourcecode (2014)

#64

Post by Iwan-Zotow »

hinoki wrote: post #3
post-factum wrote: post #2

705 /* 706 * Iterate through the groups which hold BACKUP superblock/GDT copies in an 707 * ext4 filesystem. The counters should be initialized to 1, 5, and 7 before 708 * calling this for the first time. In a sparse filesystem it will be the 709 * sequence of powers of 3, 5, and 7: 1, 3, 5, 7, 9, 25, 27, 49, 81, ... 710 * For a non-sparse filesystem it will be every group: 1, 2, 3, 4, ... 711 */ 712 static unsigned…

Yeah, maybe calling them pow3, pow5, pow7 would be a bit clearer? But a 10s search for a comment cleared it up, so I don’t really see the problem...

it is IRRATIONAL code (maybe rational within context, but ...)

Re: `three = 1` in the Linux sourcecode (2014)

#65

Post by m463 »

kortex wrote: post #26
ronyeh wrote: post #11

Earlier quoted context omitted.

I see a problem: https://github.com/torvalds/linux/blob/master/fs/ext4/resize... Upon a quick code review, these lines look buggy: unsigned three = 1; unsigned five = 5; unsigned seven = 7; Without digging deeper, the reader of this code thinks "The first line surely must be a bug, right???"

unsigned three = 1; To me, that is a 20 foot tall neon orange flashing Chesterton's fence. I think, "surely there is a very strong reason for this." Maybe not a good reason, but definitely a compelling one.

Take down the fence. It's in the filesystem code, what could go wrong?

Re: `three = 1` in the Linux sourcecode (2014)

#66

Post by waynesonfire »

CWuestefeld wrote: post #36

Many years ago in an age of klocs and flowcharts, at a large three-letter computer company, there were iron-clad coding rules that must be obeyed, no questions allowed. In general you could see their reasoning, but such bureaucratic reasoning doesn't pay off. One example of this was that all numeric values used in a program must be factored out as symbolic constants. The reason for doing this is obvious, but it faile…

'zero' and '0' are the same label, for the digit 0. There is no advantage to re-defining it, in fact, it does the opposite. It's a good practice to define labels for magic numbers to promote more maintainable code through the DRY / single source of truth principle, document the magic number through the label name, and improve code archeology by enabling searching by label.

These principles hold when the label given a clear and concise name--which is an art.

Re: `three = 1` in the Linux sourcecode (2014)

#67

Post by nneonneo »

yiyus wrote: post #55
CWuestefeld wrote: post #36

Many years ago in an age of klocs and flowcharts, at a large three-letter computer company, there were iron-clad coding rules that must be obeyed, no questions allowed. In general you could see their reasoning, but such bureaucratic reasoning doesn't pay off. One example of this was that all numeric values used in a program must be factored out as symbolic constants. The reason for doing this is obvious, but it faile…

I would do this: #define I 1 #define II 2 #define III 3 ... #define XIII 13 There is no zero in roman numerals, but you can use NULL for extra fun! (yes, I am a bad person)

Or, just program in INTERCAL (https://en.wikipedia.org/wiki/INTERCAL)! Integers are input in English (e.g. THREE FIVE NINE) and output in Roman numerals.

Re: `three = 1` in the Linux sourcecode (2014)

#70

Post by loa_in_ »

yoz-y wrote: post #41
hannasanarion wrote: post #39

Earlier quoted context omitted.

Why is the reason for doing this obvious? I can't see any benefit. I get why you would prefer to name constants for their use, like `numIterations=3` or whatever, but renaming every integer seems senseless.

It's "obvious" if you take into account the corporate culture I guess. The rule of 'no magic numbers' is generally good, but then one has to remember that some numbers (like 0 and 1) are not magic.

0 and 1 can be magic if the context depends on them being arbitrarily 0 or 1. eg.

// this byte is unused and always 0

#define UNUSED_CONSTANT_FIELD_VALUE 0

bytes = {HEADER, UNUSED_CONSTANT_FIELD_VALUE, [...]}

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