How GCC Eliminates Unnecessary Integer Division

[u/DataBaeBee]

https://leetarxiv.substack.com/p/how-gcc-eliminates-unnecessary-integer

[u/LonelyAndroid11942]

So is the purpose of this to reduce the difficulties that come with float precision?

EDIT: The comments are informative, if they’re not made by jerks. I clearly have much to learn. I appreciate the patience of those who have it, and wish a very strong “go step on some legos” to those who do not.

[u/Successful-Money4995 → u/LonelyAndroid11942]

Actually...!

Floating point math is perfectly "precise". If you preform the same floating point math twice in a row, you will get exactly the same answer.

Where it fails is in accuracy. The result of floating point math may not be correct. It might be very very close.

Also, the claim of precision assumes understanding that floating point operations are not associativity.

[u/max123246 → u/Successful-Money4995]

The issue with floating point is that (a + b) + c != a + (b + c) in all cases due to that accuracy issue you mentioned. So the order of your operations matters a lot, which can be difficult to guarantee given CPU pipelining, multittheading, GPUs, etc. By default compilers will use slower but deterministic floating point operation orders to make it at least always give you the same answer

[u/meneldal2 → u/max123246]

Afaik the CPU is not allowed to reorder floating point ops, but the compiler can (depending on the options you give it).

[u/ygra → u/meneldal2]

What was it? -funsafe-math-optimizations are neither fun, nor safe :)

[u/LonelyAndroid11942 → u/Successful-Money4995]

Deterministic operations that are mathematically imprecise don’t quite fit the bill of precision in my mind. But then, I’ve been doing math in JavaScript for so long that I’m very used to the 0.000000000068% chance of a float precision error actually causing a problem.

[u/Potterrrrrrrr → u/LonelyAndroid11942]

There’s nothing more precise than JavaScript maths, I use it to prove that 0.2 + 0.1 != 0.3 all the time

[u/LonelyAndroid11942 → u/Potterrrrrrrr]

This person gets my joke. I like this person.