sofars 0.6.0

Pure Rust implementation of the IAU SOFA library
Documentation 
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use crate::coords::ltecm;
use crate::vm::{anp, anpm, c2s, s2c, trxp};

/// Transformation from ecliptic coordinates (mean equinox and ecliptic
/// of date) to ICRS RA,Dec, using a long-term precession model.
///
/// Status:  support function.
///
/// Given:
///    epj     f64    Julian epoch (TT)
///    dl,db   f64    ecliptic longitude and latitude (radians)
///
/// Returned:
///    dr,dd   f64    ICRS right ascension and declination (radians)
///
/// Notes:
///
/// 1) No assumptions are made about whether the coordinates represent
///    starlight and embody astrometric effects such as parallax or
///    aberration.
///
/// 2) The transformation is approximately that from ecliptic longitude
///    and latitude (mean equinox and ecliptic of date) to mean J2000.0
///    right ascension and declination, with only frame bias (always
///    less than 25 mas) to disturb this classical picture.
///
/// 3) The Vondrak et al. (2011, 2012) 400 millennia precession model
///    is used.  It agrees with the IAU 2006 precession at J2000.0 and
///    stays within 100 microarcseconds during the 20th and 21st
///    centuries.  It is accurate to a few arcseconds throughout the
///    historical period, worsening to a few tenths of a degree at the
///    end of the +/- 200,000 year time span.
///
/// Called:
///    s2c       spherical coordinates to unit vector
///    ltecm     ICRS to ecliptic rotation matrix, long-term
///    trxp      product of transpose of r-matrix and p-vector
///    c2s       unit vector to spherical coordinates
///    anp       normalize angle into range 0 to 2pi
///    anpm      normalize angle into range +/- pi
pub fn lteceq(epj: f64, dl: f64, db: f64) -> (f64, f64) {
    let mut v2 = [0.0; 3];

    /* Spherical to Cartesian. */
    let v1 = s2c(dl, db);

    /* Rotation matrix, ICRS equatorial to ecliptic. */
    let rm = ltecm(epj);

    /* The transformation from ecliptic to ICRS. */
    trxp(&rm, &v1, &mut v2);

    /* Cartesian to spherical. */
    let (a, b) = c2s(&v2);

    /* Express in conventional ranges. */
    (anp(a), anpm(b))
}