rfa 0.5.9

A port ERFA to Rust.
Documentation 
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use crate::{rfam::*, utils::*};
use crate::vector_matrix::angle_ops::anp::anp;
///  Earth rotation angle (IAU 2000 model).
///
///  Given:
///   * dj1,dj2 UT1 as a 2-part Julian Date (see note)
///
///  Returned (function value):
///   * Earth rotation angle (radians), range 0-2pi
///
/// # Notes:
///
///  1) The UT1 date dj1+dj2 is a Julian Date, apportioned in any
///     convenient way between the arguments dj1 and dj2.  For example,
///     JD(UT1)=2450123.7 could be expressed in any of these ways,
///     among others:
///
///    |    dj1      |      dj2     |                      |
///    |-------------|--------------|----------------------|
///    |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 and MJD methods are good compromises
///     between resolution and convenience.  The date & time method is
///     best matched to the algorithm used:  maximum precision is
///     delivered when the dj1 argument is for 0hrs UT1 on the day in
///     question and the dj2 argument lies in the range 0 to 1, or vice
///     versa.
///
///  2) The algorithm is adapted from Expression 22 of Capitaine et al.
///     2000.  The time argument has been expressed in days directly,
///     and, to retain precision, integer contributions have been
///     eliminated.  The same formulation is given in IERS Conventions
///     (2003), Chap. 5, Eq. 14.
///
/// # Called:
///     anp       normalize angle into range 0 to 2pi
///
/// # References:
///   * Capitaine N., Guinot B. and McCarthy D.D, 2000, Astron.
///     Astrophys., 355, 398-405.
///   * McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
///     IERS Technical Note No. 32, BKG (2004)
///
///  This revision:  2021 May 11
pub fn era00(dj1: f64, dj2: f64)->f64
{
    let d1: f64; let d2: f64;
 
 
 /* Days since fundamental epoch. */
    if dj1 < dj2 {
       d1 = dj1;
       d2 = dj2;
    } else {
       d1 = dj2;
       d2 = dj1;
    }
    let t = d1 + (d2- URSA_DJ00);
 
 /* Fractional part of T (days). */
    let f = fmod(d1, 1.0) + fmod(d2, 1.0);
 
 /* Earth rotation angle at this UT1. */
    anp(URSA_D2PI * (f + 0.7790572732640
                             + 0.00273781191135448 * t))

  }