sofars 0.6.0

Pure Rust implementation of the IAU SOFA library
Documentation 
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use std::ops::Rem;

use crate::consts::{D2PI, DAS2R, DJ00, DJC};
use crate::pnp::{nut80, obl80};
use crate::vm::anpm;

///  Equation of the equinoxes, IAU 1994 model.
///
///  This function is part of the International Astronomical Union's
///  SOFA (Standards of Fundamental Astronomy) software collection.
///
///  Status:  canonical model.
///
///  Given:
///  ```
///     date1,date2   double     TDB date (Note 1)
///  ```
///  Returned (function value):
///  ```
///                   double     equation of the equinoxes (Note 2)
///  ```
///  Notes:
///
///  1) The date date1+date2 is a Julian Date, apportioned in any
///     convenient way between the two arguments.  For example,
///     JD(TT)=2450123.7 could be expressed in any of these ways,
///     among others:
///  ```
///            date1          date2
///
///         2450123.7           0.0       (JD method)
///         2451545.0       -1421.3       (J2000 method)
///         2400000.5       50123.2       (MJD method)
///         2450123.5           0.2       (date & time method)
///  ```
///     The JD method is the most natural and convenient to use in
///     cases where the loss of several decimal digits of resolution
///     is acceptable.  The J2000 method is best matched to the way
///     the argument is handled internally and will deliver the
///     optimum resolution.  The MJD method and the date & time methods
///     are both good compromises between resolution and convenience.
///
///  2) The result, which is in radians, operates in the following sense:
///
///        Greenwich apparent ST = GMST + equation of the equinoxes
///
///  Called:
///  ```
///     iauAnpm      normalize angle into range +/- pi
///     iauNut80     nutation, IAU 1980
///     iauObl80     mean obliquity, IAU 1980
///  ```
///  References:
///
///     IAU Resolution C7, Recommendation 3 (1994).
///
///     Capitaine, N. & Gontier, A.-M., 1993, Astron.Astrophys., 275,
///     645-650.
pub fn eqeq94(date1: f64, date2: f64) -> f64 {
    // double t,  om,  dpsi,  deps,  eps0, ee;

    /* Interval between fundamental epoch J2000.0 and given date (JC). */
    let t = ((date1 - DJ00) + date2) / DJC;

    /* Longitude of the mean ascending node of the lunar orbit on the */
    /* ecliptic, measured from the mean equinox of date. */
    let om = anpm(
        (450160.280 + (-482890.539 + (7.455 + 0.008 * t) * t) * t) * DAS2R
            + (-5.0 * t).rem(1.0) * D2PI,
    );

    /* Nutation components and mean obliquity. */
    let (dpsi, _) = nut80(date1, date2);
    let eps0 = obl80(date1, date2);

    /* Equation of the equinoxes. */
    let ee = dpsi * eps0.cos() + DAS2R * (0.00264 * om.sin() + 0.000063 * (om + om).sin());

    ee
}