era.a2tf.md

eraA2tf

[sign, ihmsf] = ERFA.a2tf(ndp, angle)

Decompose radians into hours, minutes, seconds, fraction.

Given:

   ndp     int     resolution (Note 1)
   angle   double  angle in radians

Returned:

   sign    char*   '+' or '-'
   ihmsf   int[4]  hours, minutes, seconds, fraction

Notes:

1) The argument ndp is interpreted as follows:

   ndp         resolution
    :      ...0000 00 00
   -7         1000 00 00
   -6          100 00 00
   -5           10 00 00
   -4            1 00 00
   -3            0 10 00
   -2            0 01 00
   -1            0 00 10
    0            0 00 01
    1            0 00 00.1
    2            0 00 00.01
    3            0 00 00.001
    :            0 00 00.000...

2. The largest positive useful value for ndp is determined by the size of angle, the format of doubles on the target platform, and the risk of overflowing ihmsf[3]. On a typical platform, for angle up to 2pi, the available floating-point precision might correspond to ndp=12. However, the practical limit is typically ndp=9, set by the capacity of a 32-bit int, or ndp=4 if int is only 16 bits.

3. The absolute value of angle may exceed 2pi. In cases where it does not, it is up to the caller to test for and handle the case where angle is very nearly 2pi and rounds up to 24 hours, by testing for ihmsf[0]=24 and setting ihmsf[0-3] to zero.

Called:

   eraD2tf      decompose days to hms

This revision: 2021 May 11

Copyright (C) 2013-2021, NumFOCUS Foundation. Derived, with permission, from the SOFA library.