CCSD3ZF0000100000001NJPL3IF0PDS200000001 = SFDU_LABEL RECORD_TYPE = STREAM OBJECT = TEXT NOTE = "Description of software provided with the Voyager CD-ROM set." END_OBJECT END ---------------------- Decompression Software ---------------------- The SOFTWARE directory contains software files for the decompression of compressed image files. In order to make the software available to a wide community of users, versions of the decompression software exist for VAX/VMS, IBM PC, Macintosh, and UNIX systems. These different sets are stored in the subdirectories VAX, PC, MAC and UNIX along with accompanying documentation. The software modules supplied are of the following types: Stand-alone executable programs C-language program source code C-language subroutine source code C-language test program source code FORTRAN program source code FORTRAN subroutine source code FORTRAN test program source code Some modification of these routines may be required in order to adapt the software to a particular computer and operating system. In addition to the decompression software, the subdirectories contain FORTRAN source code for a sample utility program to read the image index flat table. These routines assume that the user can access the compressed image files through normal system input/output (I/O) commands. Otherwise special utilities may be needed to move image files from the CD-ROM to the user's fixed-disk prior to executing the decompression programs. Information describing the compressed image files can be found in the VOLINFO.TXT file located in the DOCUMENT directory. The document describes the organization of the CD-ROM. It provides information on how to access files stored on a CD-ROM, and gives details on the format and contents of the image files and their supporting supplemental files. The practice of distributing software on read-only archival media is known to be risky. No guarantee is made that the executables will work in specific computer configurations. A Programmer's View ------------------- From the programmer's view point, the calling sequence of these routines are as follows: 1. First, extract the encoding histogram from the image file. (Consult VOLINFO.TXT document for details). The encoding histogram contains 511 32-bit elements. Note, the encoding histogram is configured in "least significant byte first" order. This is the order for integer values used by VAX and IBM PC computer systems. Users of other computer architectures (IBM Mainframes, Macintosh, SUN, and Apollo) will need to swap the byte pairs 1 and 4, and 2 and 3. (Example, hexadecimal value AA BB CC DD becomes DD CC BB AA.) 2. Pass the encoding histogram to the DECMPINIT routine to initialize the Huffman coding tree. 3. After the initialization call, read compressed image lines, one at a time, from the image file and pass the lines to the DECOMPRESS routine for restoration. After the image line has been restored, transfer the line to an output image file or display screen.