Make this work with overflow checks

[japaric]

Some math functions currently panic when compiled with overflow checks enabled (which is the default for dev builds). To fix this problem the Wrapping newtype and/or wrapping ops needs to be used in some parts of the implementations.

To test that this works with overflow checks enabled uncomment this line in ci/script.sh.

[vjackson725]

I've done some work on this. It's not very principled at the moment, I just ran the tests on debug mode.

I'm investigating fuzzing to see if I can get better coverage.

Link: issue-4

[japaric]

Just want to note that this is not needed to get math support in wasm / core because the math functions will be compiled in release mode. It is however required to use the libm crate with the dev profile.

[little-arhat]

What 's the status of this issue (and #142)? AFAIK, it blocks rust-num/num-traits#75 .

[vjackson725]

I haven't done anything since I commented, fuzzing was taking to long on my laptop. I'll send a pull request for what I did, which won't be guaranteed to fix all the problems, but should be an improvement.

[vjackson725]

I'm getting linker errors, so I will be delayed a bit.

[vjackson725]

I am getting linker errors when running cross test --target x86_64-unknown-linux-gnu, and I'm not sure how to fix the problem. There seem to be two issues here.

One is that it can't find thou_shalt_not_panic.
unwind_error.txt

Replacing thou_shalt_not_panic with an infinite loop doesn't help. This one's probably related to rust-lang/rust#47493.
unwind_error2.txt

[MarkSwanson]

Just a fyi: I found a case that may need to use wrapping:

use libm::F64Ext; // adds methods to `f64`
pub fn sqrt(x: f64) -> f64 {
    x.sqrt()
}

Calling sqrt(2.0) in debug mode gives me: (using git master branch Oct 31, 2018)

thread 'math1' panicked at 'attempt to add with overflow', /home/mswanson/.cargo/git/checkouts/libm-62d0d08057355aaa/3559e70/src/math/sqrt.rs:180:18

[Razican]

I also get addition overflow panics with sqrt() at lines 138, 144 and 159 of the file.

[Razican]

I did some fixes here that fix the issues I was having using the vsop87 crate. Not sure if this is how we should fix them, given that the Wrapping API is nightly-only.

[jackmott]

I got a subtract with overflow panic on floorf.rs just now.
Is there a way to use a function attribute to disable these checks?