I already found when it broke:
passes: rustup default nightly-2024-07-29 && cargo test --doc
fails: rustup default nightly-2024-07-30 && cargo test --doc
But reading Commits · rust-lang/rust · GitHub didn't help me to narrow it down. (It's about float precision during the computation of exp. Now depending on which branch of my code it took, the result is slightly different, only for that float function)
(the failure for the curious: Miri · tdelmas/typed_floats@83d574c · GitHub . It has nothing to do with Miri, except the fact that it uses nightly)
stderr:
thread 'main' panicked at typed_floats/src/types/mod.rs:9:1:
assertion `left == right` failed
left: Positive(2.7182818284590455)
right: 2.718281828459045
kornel
August 14, 2024, 10:39pm
2
There's a tool to do exactly that:
Bisects rustc, either nightlies or CI artifacts
4 Likes
I didn't bisect but this seems likely.
opened 11:34AM - 30 Jul 24 UTC
C-bug
T-libs
A-floating-point
regression-untriaged
Our CI started to report an error today with nightly on Linux (other platforms a… re fine).
Simplified the test case is because of a small difference in the computation of `log`.
(I know it's bad practice to do equality tests on float, but I thought I'd report this behavior change anyway as i don't know if this was intentional).
### Code
I tried this code:
```rust
fn main() {
println!("Hello, world! {}", 9f64.log(3.) );
assert_eq!(9f64.log(3.) , 2.)
}
```
I expected to see this happen:
`Hello, world! 2` and no panics. As this happens in stable
Instead, this happened:
```
Hello, world! 2.0000000000000004
thread 'main' panicked at src/main.rs:3:5:
assertion `left == right` failed
left: 2.0000000000000004
right: 2.0
```
### Version with regression
rustc 1.82.0-nightly (612a33f20 2024-07-29)
(Linux only)
2 Likes
Thank you both!
With the suggestion of cargo-bisect-rustc from @kornel I have confirmed that it was indeed `f64::log` precision change in 1.82 nightly · Issue #128386 · rust-lang/rust · GitHub as suggested by @quinedot !
********************************************************************************
Regression in 80d8270d8488957f62fbf0df7a19dfe596be92ac
********************************************************************************
Update compiler_builtins to 0.1.114 by nicholasbishop · Pull Request #125016 · rust-lang/rust · GitHub
Which does update compiler-builtins from 0.1.105 to 0.1.114 and the issue `f64::log` precision change in 1.82 nightly · Issue #128386 · rust-lang/rust · GitHub found its source in Fix math libraries not being linked on some platforms by Amjad50 · Pull Request #594 · rust-lang/compiler-builtins · GitHub , merged into the 0.1.110
1 Like
system
November 13, 2024, 1:02am
5
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