Table of contents
CSPICE_DLAFPS finds the segment preceding a specified segment in a DLA
file.
Given:
handle the integer handle associated with the file to be searched.
help, handle
LONG = Scalar
This handle is used to identify the file in subsequent calls
to other DLA or DAS routines.
dladsc the descriptor of a DLA segment in the file associated with
`handle'.
help, dladsc
LONG = Array[SPICE_DLA_DSCSIZ]
The descriptor of the segment preceding `dladsc' is sought.
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
+---------------+
the call:
cspice_dlafps, handle, dladsc, prvdsc, found
returns:
prvdsc the descriptor of the DLA segment preceding the segment
associated with the input argument `dladsc'.
help, prvdsc
LONG = Array[SPICE_DLA_DSCSIZ]
`prvdsc' is valid only if the output argument `found' is
True
found a logical flag indicating whether the previous segment was
found.
help, found
BOOLEAN = Scalar
`found' has the value True if the segment was found;
otherwise `found' is False.
SPICE_DLA_DSCSIZ
is the size of a SPICELIB DLA descriptor, defined in
IcyDLA.pro.
Any numerical results shown for this example may differ between
platforms as the results depend on the SPICE kernels used as input
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.
PRO dlafps_ex1
;;
;; IcyUser is a file that makes certain variables global.
;; You must call IcyUser to have access to the parameters used
;; in this example.
;;
;; To use the variables in IcyUser, add the 'src/icy' directory
;; to your IDL path by doing the following in which /path/to is the
;; local path to Icy.
;;
;; pref_set, 'IDL_PATH', '/path/to/icy/src/icy:<IDL_DEFAULT>', $
;; /COMMIT
;;
@IcyUser
;;
;; Prompt for the name of the file to search.
;;
fname = ' '
read, fname, PROMPT = 'Name of DLA file > '
;;
;; 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.
;;
cspice_dasopr, fname, handle
;;
;; Count the segments in the file; this allows us
;; to label the segments in our display.
;;
nsegs = 0L
cspice_dlabbs, handle, dladsc, found
while ( found ) do begin
nsegs = nsegs + 1L
currnt = dladsc
cspice_dlafps, handle, currnt, dladsc, found
endwhile
;;
;; Begin a backward search. Let `dladsc' contain
;; the descriptor of the last segment.
;;
segno = nsegs + 1L
cspice_dlabbs, handle, dladsc, found
while ( found ) do begin
;;
;; Display the contents of the current segment
;; descriptor.
;;
segno = segno - 1L
print, ' '
print, ' '
print, 'Segment number = ', segno
print, ' '
print, 'Backward segment pointer = ', $
dladsc[SPICE_DLA_BWDIDX]
print, 'Forward segment pointer = ', $
dladsc[SPICE_DLA_FWDIDX]
print, 'Character component base address = ', $
dladsc[SPICE_DLA_CBSIDX]
print, 'Character component size = ', $
dladsc[SPICE_DLA_CSZIDX]
print, 'D.p. base address = ', $
dladsc[SPICE_DLA_DBSIDX]
print, 'D.p. component size = ', $
dladsc[SPICE_DLA_DSZIDX]
print, 'Integer base address = ', $
dladsc[SPICE_DLA_IBSIDX]
print, 'Integer component size = ', $
dladsc[SPICE_DLA_ISZIDX]
print, ' '
;;
;; Find the previous segment.
;;
;; To avoid using `dladsc' as both input and output
;; in the following call, we copy `dladsc'
;; into the variable `currnt'. We then find the
;; segment preceding `currnt'.
;;
currnt = dladsc
cspice_dlafps, handle, currnt, dladsc, found
endwhile
;;
;; Close the file using the DAS close routine.
;;
cspice_dascls, handle
END
When this program was executed on a Mac/Intel/IDL8.x/64-bit
platform, using the DSK file named phobos512.bds, the output
was:
Name of DLA file > phobos512.bds
Segment number = 1
Backward segment pointer = -1
Forward segment pointer = -1
Character component base address = 0
Character component size = 0
D.p. base address = 0
D.p. component size = 4737076
Integer base address = 11
Integer component size = 29692614
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. A backward traversal may be started from any segment in
the file; it is not necessary to call cspice_dlabbs first. The role of
cspice_dlabbs is simply to return the descriptor of the last segment in
the file.
1) If the input file handle is invalid, an error is
signaled by a routine in the call tree of this routine.
2) If a failure occurs while reading the DLA file, an error
is signaled by a routine in the call tree of this routine.
3) If any of the input arguments, `handle' or `dladsc', is
undefined, an error is signaled by the IDL error handling
system.
4) If any of the input arguments, `handle' or `dladsc', is not of
the expected type, or it does not have the expected dimensions
and size, an error is signaled by the Icy interface.
5) If any of the output arguments, `prvdsc' or `found', is not a
named variable, an error is signaled by the Icy interface.
See description of input argument `handle'.
None.
DAS.REQ
DLA.REQ
ICY.REQ
None.
J. Diaz del Rio (ODC Space)
-Icy Version 1.0.0, 16-JUL-2021 (JDR)
find previous segment in DLA file
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