Location

library/std/src/f64.rs:793

Summary

The f64::atan2 function documentation specifies that the output could be in the range (-PI, PI]. However its not true. It could return -PI as well.
Following is from the function documentation:

/// * `x = 0`, `y = 0`: `0`
/// * `x >= 0`: `arctan(y/x)` -> `[-pi/2, pi/2]`
/// * `y >= 0`: `arctan(y/x) + pi` -> `(pi/2, pi]`
/// * `y < 0`: `arctan(y/x) - pi` -> `(-pi, -pi/2)`

Example case:
f64::atan2(-0.0, -1.0) returns -f64::PI