getting a Projection by from_control_points makes program freezing

[kingrongH]

This occurs every time you run the program. Here is the minimal code.

fn main() -> Result<(), Box<dyn Error>>{
    println!("get a projection from control points...");
    let from = [(0.0, 0.0), (250.0, 17.481735), (7.257017, 82.94814), (250.0, 104.18543)]; 
    let to = [(0.0, 0.0), (249.0, 0.0), (0.0, 105.0), (249.0, 105.0)];
    let projection = Projection::from_control_points(from, to);
    match projection {
        Some(_p) => println!("new projection"),
        None => println!("failed")
    }
    Ok(())
}

Here is all the output I get, nothing else:

I think Projection::from_control_points should either return Some(_) or None, rather than just keeps freezing.
Thanks all the work you have done! This may be a bug, please someone check it.

[theotherphil]

I see "failed" printed when running in both debug and release modes using the following toolchain:

stable-x86_64-apple-darwin (default)
rustc 1.40.0 (73528e339 2019-12-16)

Which compiler version and architecture are you using?

[kingrongH]

sorry I forgot to mention that, my toolchain：

stable-x86_64-unknown-linux-gnu (default)
rustc 1.41.0 (5e1a79984 2020-01-27)

[kingrongH]

I just run this demo using 1.40.0, still get freezing.
I'm using Pop!_OS 19.10

[Palladinium]

I can confirm 100% CPU usage and freezing from the example on imageproc 0.20.0.

Running Arch Linux x84_64, and tested on both debug and release with all of:

• rustc 1.45.0-nightly (a74d1862d 2020-05-14)
• rustc 1.44.0-beta.4 (02c25b359 2020-05-23)
• rustc 1.43.1 (8d69840ab 2020-05-04)

Doing some basic profiling (flamegraph) points to somewhere inside the svd() call, so maybe the issue lies within rulinalg.
This issue looks like a likely cause.

Linear algebra is a bit out of my depth, but given that from_control_points is the only use of rulinalg in imageproc it might be worth looking at switching to a different implementation of SVD.

From some very cursory research it looks like nalgebra is a viable substitute, although it might not be sufficient due to this issue.
nalgebra_lapack avoids the issue but requires a non-Rust dependency, which may be undesirable.

Perhaps a feature gate for the SVD implementation would help with getting the best of both worlds.