Function:     FTSD_RDBLE

Purpose:      Reads a FITS double descriptor from a FITS header.

Category:     FITS

File:         ftsd_access.c

Author:       K.G. Begeman

Use:          INTEGER FTSD_RDBLE( HEADER,      Input     CHARACTER*(*)
                                  DESCRIPTOR,  Input     CHARACTER*(*)
                                  VALUE )      Output    DOUBLE*(*)

              FTSD_RDBLE    Returns:
                             >=0 : Offset of record in header
                             -1	 : FITS descriptor not present
                             -2	 : descriptor does not carry info
                             -3	 : conversion error
              HEADER        Contains FITS records where to look
                            for the descriptor.
              DESCRIPTOR    FITS descriptor to search for in HEADER.
              VALUE         If present, the contents of the FITS record
                            associated with DESCRIPTOR is returned.

Updates:
	Jun 25, 1990: KGB, Document created.
	Aug 14, 1990: Sjag; Offset of record is returned.
	Feb 23, 1996: KGB, Fortran double format allowed.
	Aug 25, 2010: JPT, Allow free format numbers.