CD-ROM Now 11/CD-ROM Now MegaDisc 11 (1995-02).iso/discs/starter/ludef5.doc

Text File | 1994-10-27 | 15.8 KB | 391 lines

 File:    LUDEF5.DOC        Date:    84-08-19
 Replaces: LUDEF4.DOC        Dated:    84-08-04

 From:    Gary P. Novosielski
 To:    All LU users

 Subj:    .LBR format definition

    This file is a revision of and obsoletes the previous
    version.  Revised material is indicated by a vertical
    bar (|) to the left of the text.

 0. Introduction
|   This is the fifth revision of the formal definition of
 the format of library (.LBR) files as used by the LU Library
 Utility program and the LRUN command-file load-and-go utility.
|   Many thanks to all of those who have taken the time to
|make suggestions for improvements to this definition.  Purely
|voluntary compliance with this standard by scores of program-
|mers on many differing operating systems has allowed the .LBR
|format to evolve into a successful exchange tool in many
|segments of the computing community.  Additional suggestions
|are encouraged.
|   Please note that the current version of LU does not support
|the full directory format as defined here.  This revision has
|been distributed as an aid to programmers working on various
|other programs on non-CP/M operating systems, to allow support
|for new features in a standardized manner.

 1. Library Overview
|   A library is a data file which is assumed to be logically
 divided into one or more subparts called members.  The library
 may have any filename and filetype, except that ".LBR" is
 considered to be the default filetype.  Programs must assume
 and may optionally require the .LBR extension on any file
 which is to be treated as a library.

 2. Disk Access Method
    Libraries are usually treated as Random Record files by
 programs, but must never contain unallocated "holes" which
 are normally allowed in Random Record files.  A library can
 therefore be safely treated as a sequential file if desired.
    This allows copy programs, compacting programs, and remote
 transfer programs to process the library sequentially, and to
 safely make the assumption that the first occurrence of a
 no-record-found condition truly indicates the physical end of
 the library.

 3. Internal Organization
    A library must contain at least one member, the directory,
 and may contain an arbitrary number of other members, up to
 the limits of file size imposed by the operating system.  The
 library may also contain unused sectors which are not assigned
 to any member.  These sectors may occur as a result of the
 deletion of members, or of an unsuccessful add operation.
    There are no constraints on the contents of members, except
 for the directory, which is always the first member in the
|library, and has a specific format defined later.  The entire
|library file and each of its members are conceptually
|organized into "sectors", each sector being 128 bytes long.
 Each sector of the file belongs to at most one library member.
|Each member comprises a whole number of sectors.  The last
|sector of a member may, however, be logically declared as a
|"Short Sector".  Although it physically contains 128 bytes,
|a Short Sector contains one or more "pad" bytes at the end
|for the purpose of maintaining the structure of the library
 file as a whole.  A member may have as few as 0 sectors.

    Members may be referred to by a name of up to 8 characters,
 and an extension of up to 3 characters.  The naming rules
 are identical to those for the naming of CP/M-80 disk files.
|Members must be uniquely named; any given combination of name
|and extension may identify at most one member.

    The start and end points of each member are defined by the
 pointers in a "directory entry" for the member.  There are no
 embedded start or end marks separating the members.  All
 sectors between the start and end sectors of a member belong
|to that member.  The members need not appear in the library
|in the same order that their directory entries appear in the
|directory.  Thus the directory may be sorted, within certain
|ordering constraints defined below, without physically moving
|the members themselves.

 4. Directory Format
    The directory is the first member of a library, and must
 begin in sector 0 of the file.  It must contain at least one
 sector, and may contain an arbitrary number of sectors.  The
|directory may not contain a Short Sector.
    The directory is composed of entries.  Each entry is 32
 bytes in length, so that the number of entries is equal to
 four times the number of sectors in the directory.  The
|number of entries present determines the maximum number of
|members in the library.  Each directory entry contains the
|name, starting point, size, and other information for one
|of the members in the library.
    Each entry is initialized to one of three possible states:
 Active, Deleted, or Unused.  The first entry is always active,
 and is the entry corresponding to the directory itself.
    Unused entries always occur after all active and deleted
 entries.  If the directory is scanned beginning with the
 first entry, and an unused entry is found, then all remaining
 entries from there through the end of the directory must also
 be tagged as unused.
    However, active and deleted entries may be mixed in any
 order.  Finding a deleted entry does not guarantee that all
 active entries have been scanned.

 5. Directory Entry Format

    The 32 bytes of each entry have the following significance:

    Byte            Meaning
    ----    ------------------------------------------
    0    STATUS  Possible values (in hexadecimal) are:
        00    Active Entry
          FE    Deleted Entry
        FF    Unused Entry
            Any other value should be treated as
        a deleted entry.

    1-8    NAME    Rules are identical with those which
            govern the naming of disk files.  Names
        shorter than the maximum are padded with
        spaces.

    9-11    EXTENSION  Rules are the same as for NAME.

    12-13    INDEX    Pointer to the first sector of the
            member within the library.  Stored as
        a two-byte binary value, least significant byte
|        first.  For example, an index of value of 9
|        indicates that the first sector of the member
|        occurs 9 sectors, or 9 * 128 = 1152 bytes from
|        the beginning of the library.

    14-15    LENGTH    The length of the member in sectors.
            Stored as a two-byte binary value,
        least significant byte first.  If this value is
        zero, then the member is empty, and the Index
        field (above) is meaningless.

    16-17    CRC    The Cyclic Redundancy Check value for
            the member.  Stored as a two-byte
        binary value, least significant byte first.
        This value is calculated using the CCITT
        algorithm as used in the widely supported
         XMODEM protocol.  If each of the bytes in the
|        member (including any pad bytes inserted in the
|        possibly "short" last sector) are processed by
|        this algorithm, followed by the two bytes of
        the CRC itself (high order first) the resulting
        value will be zero.
|           Special-case processing is required for the
|        CRC value of the directory member. See below.
|
|    The next four 16-bit words are reserved for library
|    member time and date stamping.  They are all stored
|    as two-byte binary values, least significant byte
|    first.  Programs not implementing time and date
|    stamping shall explicitly set any unused values to
|    zero when creating a new entry.  Programs must convert
|    the time and date formats, if any, defined by their own
|    operating system into the given formats to insure
|    transportability of the resulting library file.

|    18-19   CREATION DATE    The date of creation of the
|                file.  Its value may be prior
|        to the date the file was added as a member of
|        the library, if the operating system can supply
|        the original creation date of the file.  On
|        extracting the member from the library, this
|        date may be passed to the operating system for
|        its use in restoring the original creation
|        date.  The format for the date conforms to
|        Digital Research MP/M (and CP/M+) julian date
|        format.  This is a binary 16-bit integer
|        value representing the number of days since
|        December 31, 1977.  For example:  Jan 1, 1978
|        is day 1 (0001H), and July 4, 1984 is 2377
|        (0949H).  A zero value indicates this date is
|        not available.

|    20-21   LAST CHANGE DATE  The date of last change to
|                  the member.  Assumed to be
|        no earlier than the creation date, and may
|        pre-date the addition of the file as a member.
|        Storage format is identical to creation date.
|        If the operating system supplies only one file
|        date, it should be stored in Creation Date,
|        and Last Change Date left unused (set to zero.)
|        A zero value is assumed to be equal to the
|        creation date.  A program which makes any
|        in-place changes to the member while it resides
|        in the library should update the value of this
|        field with the current date if known, or if
|        not known, should overwrite with zeros.  For
|        the purpose of this definition, the performing
|        of a strictly reversable process, such as the
|        encryption, compression, or translation of a
|        member does not require a change of date.

|    22-23    CREATION TIME    If available, the time-of-day
|                corresponding to the creation
|        date as defined above.  The storage format
|        conforms to MS-DOS standards, wherein the 16-
|        bit word comprises three sub-fields as follows:
|
|        byte:    <==23==> <==22==>
|        bit:    76543210 76543210
|        field:    hhhhhmmm mmmsssss
|
|        legend:
|        h = Hours.  Treated as a 5-bit binary integer
|            in the range 0..23
|        m = Minutes.  Treated as a 6-bit binary integer
|            in the range 0..59
|        s = Seconds/2.  Treated as a 5-bit binary
|            integer in the range 0..29, allowing
|            resolution to the nearest 2-second
|            interval.  May be zeros in a system
|            supporting only hour/minutes.
|
|    24-25    LAST CHANGE TIME   If available, the time of
|                   day corresponding to the
|        Last Change Date defined above.  Format is the
|        same as Creation Time.

|    26      PAD COUNT    Valid range: 00H to 7FH.  This
|                byte is for use with non-CP/M
|        systems, such as MS-DOS and UNIX, where file
|        lengths are not necessarily a multiple of 128
|        bytes. It allows the exact size of the member
|        to be expressed in the directory entry.  The
|        value in PAD COUNT represents the number of pad
|        bytes (from 0 to 127) which were inserted in
|        the final sector of the member to bring its
|        size up to the required 128 bytes.  The value
|        of each pad byte inserted should be a hexi-
|        decimal 1A (ASCII SUB character) which is
|        a normal end-of-file mark under CP/M.
|
|        For example, a Pad Count of 10 hexidecimal (16
|        decimal) implies that the last 16 bytes of the
|        final sector of the member are pad characters,
|        i.e. that only the first 112 bytes (128-16) are
|        actually part of the member file.  The pad
|        characters may be ignored when the member is
|        extracted from the library.  The resulting file
|        is then the same length as the original.
|        Specifically, it is ((LENTH * 128) - PAD COUNT)
|        bytes long.
|
|        Note well, however, that the pad characters are
|        in fact physically present in the library file,
|        and are counted as significant characters in
|        the CRC check value calculations discussed
|        above.  This is necessary to provide downward
|        compatibility with older libraries, and with
|        programs which do not implement this feature,
|        such as CP/M-only versions of LU.  Any program
|        not implementing this feature shall explicitly
|        set this byte to zero when creating a new
|        entry.  (Libraries built by any program which
|        properly adhered to prior versions of this
|        standard have therefore been properly created.)
|        In this case, the last sector of the member
|        will be assumed to be a full 128 bytes long,
|        which was always the case in the past.

    27-31    FILLER     Reserved for future use.  In unused
              and deleted entries, these bytes are
     garbage.  In all active entries, they are explicitly
    set to binary zero.
       Any future enhancements to the .LBR format which
    make use of these bytes will recognize this zero
    value as a non-error condition to allow a library
    created with an old version of LU to be processed by
    future versions.

| 6. Directory Control Entry
|    The Directory Control Entry is always the first entry in
| the directory, and is the entry which corresponds to the
| directory member itself.  This entry is similar in form to
| any other entry, but is specified more completely here for
| clarification.
|
|     STATUS        Always 00, Active.  The directory must
|            always be an active member.
|
|    NAME        Always 8 blanks.  This is the unique
|            name of the directory member.
|
|    EXTENSION    Always 3 blanks.
|
|    INDEX        Always 0000; the directory must be
|            physically located at the beginning of
|            the library file.
|
|    LENGTH        Never 0000.  The directory must contain
|            at least one sector.  The actual length
|            of the directory is found here.
|
| If any program finds, in the first sixteen bytes of a library
| file, one or more values which conflict with the above
| specifications, this fact shall be interpreted as a fatal
| indication that the file is not a valid LBR-format library.
| Errors in the following bytes are non-fatal:
|
|    CRC        Since the directory contains its own
|            entry, and hence its own CRC value, a
|    logical conflict would arise if the CRC value were
|    calculated in the normal manner.  The act of storing
|    the CRC value in the entry would render it invalid.
|    For this reason, the CRC value of the directory member
|    is calculated after explicitly storing a 0000 value
|    in the CRC word of the first entry.  The resulting
|    calculated value is then stored in this word before
|    closing the library.
|        When checking the CRC of an existing directory, the
|    old CRC value in the first entry is saved in temporary
|    storage and replaced by 0000 before calculating the
|    new CRC value.  The old and new values should then be
|    compared for equality.

    CREATION DATE    If used, the date of creation of the
            library.  Reorganization of the library
    to reclaim space may leave this date unchanged.

    LAST CHANGE DATE  If used, the date of last change to
              the directory.  The directory is
    changed by adding, deleting, or renaming members, and
    by reorganizing the library.

    CREATION TIME    If used, the time of creation of the
            library.

    LAST CHANGE TIME  If used, the time of last change to
              the directory.

    PAD COUNT    Value ignored and assumed 0. Directory
            sectors are always a full 128 bytes.
    Set to 0 when library is created or reorganized.

    FILLER        Set to 0 as in any other entry.

 Notes:
    In unused and deleted entries all bytes except the
    Status byte are undefined.

       The contents of any data sectors which are not
    assigned to an active member are not defined.
    They remain allocated to the .LBR file, to provide
    for sequential processing, as noted above, but no
    assumptions should be made as to their contents.
    These sectors are eliminated from the library when
    it is reorganized.

    For systems which do not implement the CRC validation
    functions, the CRC value of member entries should
|    be set to 0000.  Libraries created by very early
|    versions of LU may have garbage in the last 16 bytes
|    of the first directory entry, but all other entries
|    will conform to this convention.  These old library
|    files may generate spurious (but non-fatal) error
|    messages caused by a garbage Directory CRC.  Attempts
|    to support the detection of this condition, and the
|    supression of these error messages has become more and
|    more complex to implement, and more difficult to
|    justify.  Beginning with this definition, such attempts
|    are forsaken.  Users experiencing a problem with this
|    are encouraged to make a minor change to such libraries
|    with a version 3.0 or higher LU.  A dummy add/delete or
|    reorganization will suffice.  My appologies for any
|    inconvenience this may cause.

 6. Conclusion
    If there are any further questions, comments, or requests
 regarding library format, or if you note any ambiguities or
 contradictions in these specifications, please feel free to
 contact me.

    Gary P. Novosielski

    Voice phone: [phone]   Evenings and weekends
    MCI Mail:    GNOVOSIELSKI
    CompuServe:  [70160,120]     EMAIL or CP-MIG
    Telex:         650-195-2395    6501952395 MCI

 End of file.