Note atan2 can return -PI
#140487
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Note atan2 can return -PI
#140487
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atan2 can return -PI
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Apr 30, 2025
| /// * `x <= -0`, `y <= -0` -> `[-pi, -pi/2]` | ||
| /// * `x >= +0`, `y <= -0` -> `[-pi/2, -0]` | ||
| /// | ||
| /// Note that positive and negative 0 are distinct floating point values. |
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This is always true, what's more important is that this description is not treating them as equal.
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| /// * `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)` | ||
| /// * `x >= +0`, `y >= +0` -> `[+0, pi/2]` | ||
| /// * `x <= -0`, `y >= +0` -> `[pi/2, pi]` | ||
| /// * `x <= -0`, `y <= -0` -> `[-pi, -pi/2]` | ||
| /// * `x >= +0`, `y <= -0` -> `[-pi/2, -0]` |
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println!("{}", f32::atan2(-0.0, 0.0)); // -0
println!("{}", f32::atan2(0.0, -0.0)); // 3.1415927
println!("{}", f32::atan2(0.0, 0.0)); // 0
println!("{}", f32::atan2(-0.0, -0.0)); // -3.1415927...that's kinda fucked up huh.
I think placing the comment about negative versus positive zero after this table-ish-thing makes it harder to read. We should lead with the comment that the sign of 0.0 can affect the result, rather than being treated as equal, even though (0.0 == -0.0) == true.
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Fixes #136275