Ushering out strlcpy()

Posted Aug 29, 2022 17:08 UTC (Mon) by NYKevin (subscriber, #129325)
In reply to: Ushering out strlcpy() by Wol
Parent article: Ushering out strlcpy()

The problem is, the real numbers are uncountable, which means that there is no encoding of the real numbers in (finite-length) bit strings (even allowing for variable-length bit strings, arbitrary precision encodings, etc.). Furthermore, there exist non-computable real numbers (real numbers for which there does not exist any algorithm that can output their digits), and even if you restrict yourself to the computable reals, there are many computable numbers for which basic arithmetic is problematic (for example, zero and "2^-n, if Turing machine M halts in exactly n steps, or else zero if it never halts" are both computable numbers, but deciding whether they are equal is equivalent to the halting problem and hence undecidable).

You can't just say "it's a number" and call it a day. The math doesn't work out. You have to make some sort of compromise, and operate on some computable subset of the real numbers, which in practice is going to be a great deal smaller than the computable numbers. You can shout in ALL CAPS about how programmers should not be required to think about that compromise, but clearly somebody has to, at some point. If you just want to make the accountants happy, then use some sort of decimal fixed point (like SQL's DECIMAL type) or something similar. That's not "just a number" because it still does intermediate rounding, but at least it's doing the rounding that accountants probably want it to do.

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Ushering out strlcpy()

Posted Aug 29, 2022 18:26 UTC (Mon) by Wol (subscriber, #4433) [Link]

> You can't just say "it's a number" and call it a day. The math doesn't work out. You have to make some sort of compromise, and operate on some computable subset of the real numbers, which in practice is going to be a great deal smaller than the computable numbers. You can shout in ALL CAPS about how programmers should not be required to think about that compromise, but clearly somebody has to, at some point. If you just want to make the accountants happy, then use some sort of decimal fixed point (like SQL's DECIMAL type) or something similar. That's not "just a number" because it still does intermediate rounding, but at least it's doing the rounding that accountants probably want it to do.

:-)

Pick mostly uses decimal fixed point (and makes the programmer think about it), but it really is "a number is 14sf to 4dp unless you tell me otherwise", which is sufficient for most purposes. It's a case of "if the sort of number matters, then I need to do something about it, but "number" covers most use cases".

Apologies if I'm maligning him, but wtarreau came across as complaining about Rust's memory checking and borrow checking and all the minutiae of system programming that causes real grief it it goes wrong.

People get too bogged down in the minutiae of what they're doing, and it can be very hard to step back and ask yourself "does this REALLY matter?". Quite often the answer is "no". If the computable subset is larger than your problem space (as it usually is), do you really want to be forced to pay strict attention to it? :-) And when the answer is "yes" then you do have to pay attention.

Cheers,
Wol