astrodynamics 0.12.1

Numerical astrodynamics engine for orbit propagation, force models, and flight-dynamics primitives
Documentation 
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//! Small fixed-size 3D vector helpers.
//!
//! These helpers intentionally keep simple, explicit operation order. Callers
//! that need a parity-specific order should use the named variants rather than
//! copy-pasting a local helper.

#[inline]
pub fn add3(a: [f64; 3], b: [f64; 3]) -> [f64; 3] {
    [a[0] + b[0], a[1] + b[1], a[2] + b[2]]
}

#[inline]
pub fn sub3(a: [f64; 3], b: [f64; 3]) -> [f64; 3] {
    [a[0] - b[0], a[1] - b[1], a[2] - b[2]]
}

#[inline]
pub fn neg3(v: [f64; 3]) -> [f64; 3] {
    [-v[0], -v[1], -v[2]]
}

#[inline]
pub fn scale3(v: [f64; 3], s: f64) -> [f64; 3] {
    [v[0] * s, v[1] * s, v[2] * s]
}

#[inline]
pub fn dot3(a: [f64; 3], b: [f64; 3]) -> f64 {
    a[0] * b[0] + a[1] * b[1] + a[2] * b[2]
}

#[inline]
pub fn dot3_ref(a: &[f64; 3], b: &[f64; 3]) -> f64 {
    a[0] * b[0] + a[1] * b[1] + a[2] * b[2]
}

#[inline]
pub fn dot3_z_yx_ref(a: &[f64; 3], b: &[f64; 3]) -> f64 {
    a[2] * b[2] + (a[1] * b[1] + a[0] * b[0])
}

#[inline]
pub fn dot3_fused_z_yx_ref(a: &[f64; 3], b: &[f64; 3]) -> f64 {
    a[2].mul_add(b[2], a[1].mul_add(b[1], a[0] * b[0]))
}

#[inline]
pub fn norm3(v: [f64; 3]) -> f64 {
    dot3(v, v).sqrt()
}

#[inline]
pub fn norm3_ref(v: &[f64; 3]) -> f64 {
    dot3_ref(v, v).sqrt()
}

#[inline]
pub fn unit3(v: [f64; 3]) -> Option<[f64; 3]> {
    match norm3(v) {
        n if n > 0.0 => Some(scale3(v, 1.0 / n)),
        _ => None,
    }
}

#[inline]
pub fn unit3_ref_unchecked(v: &[f64; 3]) -> [f64; 3] {
    let n = norm3_ref(v);
    [v[0] / n, v[1] / n, v[2] / n]
}

#[inline]
pub fn cross3(a: [f64; 3], b: [f64; 3]) -> [f64; 3] {
    [
        a[1] * b[2] - a[2] * b[1],
        a[2] * b[0] - a[0] * b[2],
        a[0] * b[1] - a[1] * b[0],
    ]
}

#[inline]
pub fn cross3_ref(a: &[f64; 3], b: &[f64; 3]) -> [f64; 3] {
    [
        a[1] * b[2] - a[2] * b[1],
        a[2] * b[0] - a[0] * b[2],
        a[0] * b[1] - a[1] * b[0],
    ]
}

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

    #[test]
    fn named_dot_orders_match_their_explicit_recipes() {
        let a = [1.25, -2.5, 3.75];
        let b = [-4.0, 5.5, -6.25];

        assert_eq!(
            dot3(a, b).to_bits(),
            (a[0] * b[0] + a[1] * b[1] + a[2] * b[2]).to_bits()
        );
        assert_eq!(
            dot3_z_yx_ref(&a, &b).to_bits(),
            (a[2] * b[2] + (a[1] * b[1] + a[0] * b[0])).to_bits()
        );
        assert_eq!(
            dot3_fused_z_yx_ref(&a, &b).to_bits(),
            a[2].mul_add(b[2], a[1].mul_add(b[1], a[0] * b[0]))
                .to_bits()
        );
    }

    #[test]
    fn unit3_zero_vector_returns_none() {
        assert_eq!(unit3([0.0, 0.0, 0.0]), None);
    }
}