Convert an interval in days into hours, minutes, seconds
CALL sla_DD2TF (NDP, DAYS, SIGN, IHMSF)
number of decimal places of seconds
interval in days
`+' or `-'
hours, minutes, seconds, fraction
NDP less than zero is interpreted as zero.
The largest useful value for NDP is determined by the size
of DAYS, the format of DOUBLE PRECISION floating-point numbers
on the target machine, and the risk of overflowing IHMSF(4).
For example, on a VAX computer, for DAYS up to 1D0, the available
floating-point precision corresponds roughly to NDP=12. However,
the practical limit is NDP=9, set by the capacity of the 32-bit
The absolute value of DAYS may exceed 1D0. In cases where it
does not, it is up to the caller to test for and handle the
case where DAYS is very nearly 1D0 and rounds up to 24 hours,
by testing for IHMSF(1)=24 and setting IHMSF(1-4) to zero.