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//! Tangent approximation for a single-precision float.

use super::F32;

impl F32 {
    /// Approximates `tan(x)` in radians with a maximum error of `0.6`.
    pub fn tan(self) -> Self {
        self.sin() / self.cos()
    }
}

#[cfg(test)]
mod tests {
    use super::F32;

    /// Maximum error in radians
    // TODO(tarcieri): this is kinda bad, find a better approximation?
    const MAX_ERROR: f32 = 0.6;

    /// Tangent test vectors - `(input, output)`
    const TEST_VECTORS: &[(f32, f32)] = &[
        (0.000, 0.000),
        (0.140, 0.141),
        (0.279, 0.287),
        (0.419, 0.445),
        (0.559, 0.625),
        (0.698, 0.839),
        (0.838, 1.111),
        (0.977, 1.483),
        (1.117, 2.050),
        (1.257, 3.078),
        (1.396, 5.671),
        (1.536, 28.636),
        (1.676, -9.514),
        (1.815, -4.011),
        (1.955, -2.475),
        (2.094, -1.732),
        (2.234, -1.280),
        (2.374, -0.966),
        (2.513, -0.727),
        (2.653, -0.532),
        (2.793, -0.364),
        (2.932, -0.213),
        (3.072, -0.070),
        (3.211, 0.070),
        (3.351, 0.213),
        (3.491, 0.364),
        (3.630, 0.532),
        (3.770, 0.727),
        (3.910, 0.966),
        (4.049, 1.280),
        (4.189, 1.732),
        (4.328, 2.475),
        (4.468, 4.011),
        (4.608, 9.514),
        (4.747, -28.636),
        (4.887, -5.671),
        (5.027, -3.078),
        (5.166, -2.050),
        (5.306, -1.483),
        (5.445, -1.111),
        (5.585, -0.839),
        (5.725, -0.625),
        (5.864, -0.445),
        (6.004, -0.287),
        (6.144, -0.141),
        (6.283, 0.000),
    ];

    #[test]
    fn sanity_check() {
        for &(x, expected) in TEST_VECTORS {
            let tan_x = F32(x).tan();
            let delta = (tan_x - expected).abs();

            assert!(
                delta <= MAX_ERROR,
                "delta {} too large: {} vs {}",
                delta,
                tan_x,
                expected
            );
        }
    }

    #[test]
    fn zero() {
        assert_eq!(F32::ZERO.tan(), F32::ZERO);
    }

    #[test]
    fn nan() {
        assert!(F32::NAN.tan().is_nan());
    }
}