Procedure

   dlabbs_c ( DLA, begin backward search ) 

   void dlabbs_c ( SpiceInt         handle,
                   SpiceDLADescr  * dladsc,
                   SpiceBoolean   * found  )

Abstract

   Begin a backward segment search in a DLA file.

Required_Reading

   DAS
   DLA

Keywords

   DAS
   DLA
   FILES

Brief_I/O

   VARIABLE  I/O  DESCRIPTION
   --------  ---  --------------------------------------------------
   handle     I   Handle of open DLA file.
   dladsc     O   Descriptor of last segment in DLA file.
   found      O   Flag indicating whether a segment was found.

Detailed_Input

   handle      is the integer handle associated with the file to be
               searched. This handle is used to identify the file in
               subsequent calls to other DLA or DAS routines.

Detailed_Output

   dladsc      is the descriptor of the last DLA segment in the
               file associated with `handle'.

               The segment descriptor layout is:

                  +---------------+
                  | BACKWARD PTR  | Linked list backward pointer
                  +---------------+
                  | FORWARD PTR   | Linked list forward pointer
                  +---------------+
                  | BASE INT ADDR | Base DAS integer address
                  +---------------+
                  | INT COMP SIZE | Size of integer segment component
                  +---------------+
                  | BASE DP ADDR  | Base DAS d.p. address
                  +---------------+
                  | DP COMP SIZE  | Size of d.p. segment component
                  +---------------+
                  | BASE CHR ADDR | Base DAS character address
                  +---------------+
                  | CHR COMP SIZE | Size of character segment component
                  +---------------+

               `dladsc' is valid only if the output argument `found' is
               SPICETRUE.

   found       is a logical flag indicating whether a segment was
               found. `found' has the value SPICETRUE if the file
               contains at least one segment; otherwise `found' is
               SPICEFALSE.

Parameters

   None.

Exceptions

   1)  If the input file handle is invalid, an error is
       signaled by a routine in the call tree of this routine.

   2)  If an error occurs while reading the DLA file, the error
       is signaled by a routine in the call tree of this routine.

   3)  If the input descriptor is invalid, this routine will
       fail in an unpredictable manner.

Files

   See description of input argument `handle'.

Particulars

   DLA files are built using the DAS low-level format; DLA files are
   a specialized type of DAS file in which data are organized as a
   doubly linked list of segments. Each segment's data belong to
   contiguous components of character, double precision, and integer
   type.

   This routine supports backward traversal of a DLA file's segment
   list. Note that it is not necessary to call this routine to
   conduct a backward traversal; all that is necessary is to have
   access to the last descriptor in the file, which this routine
   provides.

Examples

   The numerical results shown for this example may differ across
   platforms. The results depend on the SPICE kernels used as input,
   the compiler and supporting libraries, and the machine specific
   arithmetic implementation.

   1) Open a DLA file for read access, traverse the segment
      list from back to front, and display segment address
      and size attributes.

      Example code begins here.


      /.
         Program dlabbs_ex1
      ./

      #include "SpiceUsr.h"
      #include "SpiceDLA.h"
      #include <stdio.h>

      int main()
      {
         /.
         Local parameters
         ./
         #define FILSIZ           256

         /.
         Local variables
         ./
         SpiceBoolean            found;
         SpiceChar               fname  [ FILSIZ ];
         SpiceDLADescr           current;
         SpiceDLADescr           dladsc;
         SpiceInt                handle;
         SpiceInt                segno;

         /.
         Prompt for the name of the file to search.
         ./
         prompt_c ( "Name of DLA file > ", FILSIZ, fname );

         /.
         Open the DLA file for read access.  Since DLA
         files use the DAS architecture, we can use DAS
         routines to open and close the file.
         ./
         dasopr_c ( fname, &handle );

         /.
         Begin a backward search. Let `dladsc' contain
         the descriptor of the last segment.
         ./
         segno = 0;

         dlabbs_c ( handle, &dladsc, &found );

         while ( found )
         {
            /.
            Display the contents of the current segment
            descriptor.
            ./

            ++segno;

            printf ( "\n"
                     "Segment number (offset from end of file) = %d\n"
                     "\n"
                     "   Backward segment pointer         = %d\n"
                     "   Forward segment pointer          = %d\n"
                     "   Integer component base address   = %d\n"
                     "   Integer component size           = %d\n"
                     "   D.p. component base address      = %d\n"
                     "   D.p. component size              = %d\n"
                     "   Character component base address = %d\n"
                     "   Character component size         = %d\n"
                     "\n",
                     (int)(segno),
                     (int)(dladsc.bwdptr),
                     (int)(dladsc.fwdptr),
                     (int)(dladsc.ibase),
                     (int)(dladsc.isize),
                     (int)(dladsc.dbase),
                     (int)(dladsc.dsize),
                     (int)(dladsc.cbase),
                     (int)(dladsc.csize)                            );

            /.
            Find the previous segment.
            ./
            current = dladsc;

            dlafps_c ( handle, &current, &dladsc, &found );
         }

         /.
         Close the file using the DAS close routine.
         ./
         dascls_c ( handle );

         return ( 0 );
      }


      When this program was executed on a Mac/Intel/cc/64-bit
      platform, using the DSK file named phobos512.bds, the output
      was:


      Name of DLA file > phobos512.bds

      Segment number (offset from end of file) = 1

         Backward segment pointer         = -1
         Forward segment pointer          = -1
         Integer component base address   = 11
         Integer component size           = 29692614
         D.p. component base address      = 0
         D.p. component size              = 4737076
         Character component base address = 0
         Character component size         = 0

Restrictions

   None.

Literature_References

   None.

Author_and_Institution

   N.J. Bachman        (JPL)
   J. Diaz del Rio     (ODC Space)

Version

   -CSPICE Version 1.1.0, 22-FEB-2021 (JDR)

       Changed the output argument name "descr" to "dladsc" for
       consistency with other routines.

       Edited the header comments to comply with NAIF standard.

   -CSPICE Version 1.0.0, 10-JAN-2017 (NJB)

Index_Entries

   begin backward search in DLA file