[This is a HTMLisation of LUDEF5.DOC, version 5 of the official LBR file format. I have removed the vertical bars (|) which in the original marked changes from version 4; these do not translate well to HTML.]
[In this file, "sector" is synonymous with "128-byte record"]
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.
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.
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.
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 disc 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.
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.
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 disc 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 [or CP/M 3], 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 hexadecimal 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.
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.
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:
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 the new CRC value is calculated. The old and new values should then be compared for equality.
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 apologies for any inconvenience this may cause.
[Note that these details may have been true in 1984. They probably aren't now].
End of file.
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