Oakland CPM Archive/oakcpm.iso/cpm/zcpr33/z33pnote.0z3/Z33PNOTE.003

Text File | 1987-06-10 | 10.3 KB | 192 lines

                          ZCPR33 PROGRAMMING NOTES
                          ========================

Note Number:    003
Author:         Jay Sage
Date:           June 6, 1987


                        The ZCPR33 File Name Parser


     There are two special aspects to the file name parser in ZCPR33.  First
of all, the command processor provides three standard entry points, similar
to those provided by the BIOS, so that external programs can make use of the
parsing code inside the command processor.  Secondly, the result of the
parsing is designed to provide much more information, such as whether or not
a directory was specified explicitly and, if so, whether or not the
directory was a valid one.  Let's take up these two features one at a time.
Note that routines are (or will be) provided in Z33LIB to perform these
functions easily.


The Parser Entry Points
-----------------------

     The beginning of the command processor has the following structure:

   offset       code
   ------       ----
     0H         JP      actual code
     3H         JR      actual code
     5H         DB      version byte
     6H         DS      ten configuration information bytes
    10H         LD      HL,token pointer
    13H         JP      PARSETAIL
    16H         JP      SCANNER
    19H         command dispatch table

     The routine whose entry point is at offset 16H parses a single file
specification string pointed to by HL into a file control block pointed to
by DE.  Two important precautions must be observed.

     First, the string at HL must have the form of a command token, that is,
it must have a termination character.  The termination characters that are
recognized are a semicolon, and equal sign, a space, or any control
character.  Note that a comma is not included in this list, so that compound
tokens such as "FN1.FT,FN2.FT" will be treated as a single token, and the
second file name and type will be skipped over.  Individual fields in a file
specification are terminated by any of the following characters: space,
equal sign, underscore, semicolon, greater than or less than sign, comma,
or null.  A second colon or period will also terminate the field.  However,
once all the required fields have been identified, the code skips over
characters until it finds the token delimiter from the smaller set of
characters described earlier.  Thus this routine does not function exactly
like the routine ZFNAME in Z3LIB.  Contrary to the statement in "ZCPR3, The
Libraries," ZFNAME does not behave identically to the ZCPR30 parser either.

     The second precaution is the more unusual one.  The file control block
pointed to by DE must have been initialized more extensively than is usual.
Generally, the fields occupied by the file name and file type do not have to
be initialized.  For this routine, however, the 11 filename characters must
all be set to spaces before the routine is called.

     The routine whose entry point is at offset 13H parses a pair of file
specifications pointed to by HL into the two system default file control
blocks (at 5CH and 6CH).  The file control blocks are initialized by the
routine, and no user-provided initialization of any sort is required.  After
this routine has run, the address of the beginning of the second of the two
file specifications is set into the word at offset 11H so that it will be
loaded into the HL register automatically when the entry point at offset 10H
is used.  The entry point at offset 10H is provided in case an external
program wants to continue parsing the line that the command processor
parsed.  This would be useful, for example, for an RCP version of SAVE or
JUMP.

     Note that these routines can be used only when the command processor
has not been overwritten by an application program.  When this is the case,
these routines offer two advantages.  First, they save code.  Secondly, they
automatically parse the file specifications in the exact same way that the
command processor does (naturally!).  This means that the same configuration
options will apply, such as recognizing DU and/or DIR forms and in the
correct order, checking passwords, omitting password checking when the wheel
byte is set, allowing the DU form only when the ENV DUOK flag is set, etc.


Structure of File Control Blocks Built
--------------------------------------

     The file control blocks constructed by the ZCPR33 parser differ in
several critical ways from those produced by the ZCPR30 command processor.
In all cases, the purpose is to provide more information.

     In its internal operation, the command processor constructs three file
control blocks.  The external file control block contains a parsed version
of the command expression (the first token on the command line, token zero).
The first two tokens in the command tail are parsed into the two system
default file control blocks.

     Let's treat the two system default file control blocks first.  These
two FCBs are initialized so that all fields contain zeros except as noted
here.

   the drive byte:

        This byte is set to zero if no drive is specified explicitly, that
        is, if there is no 'DU:', 'DIR:', or ':' (alone) prefix.  If a
        directory is specified, then a drive number in the range 1..16
        designated by that directory is stored in the drive byte.  A colon
        alone designates the currently logged directory.  If the designated
        directory is invalid for any reason, the currently logged drive is
        used (an error flag, described below, is also set).  A designated
        directory is invalid if (1) it is a 'DU:' expression with a drive or
        user number that is outside the allowed range, (2) it is a 'DIR:'
        expression with a name that is not defined in the named directory
        register (NDR), or (3) it is a 'DIR:' form designating a password-
        protected directory and the user did not enter the correct password
        when asked for it.

the file name and type fields:

        These fields are filled in with the first 8 characters of the string
        before a period and the first three characters of the string after a
        period, respectively.  If fewer than 8 and 3 characters,
        respectively, are present, the name or type is padded out with space
        characters.  If no name or no type is included in the file
        specification, then the corresponding field is filled entirely with
        blanks.  If more than 8 or 3 characters, respectively, are present,
        the excess characters are ignored.

user number byte:

        The user number byte at offset 13 decimal (0DH) contains the user
        number for the file specification.  If no user number is given
        explicitly (using either the forms 'DU:' or 'U:' or by a named
        directory specification), then this byte contains the currently
        logged in user number.  There is no way to tell whether or not a
        user number was given explicitly (thus the expression 'A:' cannot be
        distinguished from the expression 'A3:' where the current user area
        is 3).  This is a defect in the basic design of ZCPR3 file control
        blocks and cannot be changed at this point.  To overcome this
        limitation, a program would have to scan the original file
        specification itself using its own code.

record count byte:

        The record count byte at offset 0FH in the FCB normally contains a
        zero byte.  If the directory specified was not valid (for the
        reasons listed above), a non-zero value is placed in the record
        count byte.  Programs can use this information to distinguish
        between an FCB specifying the current directory because that is the
        directory actually specified and an FCB that does so because the
        specified directory was invalid.

     In a future release of the ZCPR3 command processor, it might be
possible to use individual bits in the record count byte to indicate
complete information about the parse, including whether or not a user number
was specified explicitly.


The External Command File Control Block
---------------------------------------

     The requested command is parsed into the external command file control
block in exactly the way described above.  However, since this FCB is used
by the command processor before a user program sees it, there are some
changes.

     First of all, the drive byte is always set to zero during the search
for a transient program, and it was already zero for any RCP- and CPR-
resident commands.  Consequently, it is not normally possible to get any
information about the kind of command from this byte.  However, the drive
and user number where the command was actually found during loading is put
into the FCB.  The user value is in its normal place at offset 13 (0DH).
The drive value, in the range 1..16, is kept in the next byte (this way the
two values can be loaded into BC as a word for use by SYSLIB routines like
LOGUD).  If the drive value is 0, then no search was performed for a
transient command; in other words, the command was a resident command.

     There is one exception to the above description.  That concerns the FCP
commands, which I carefully did not mention.  The command processor scans
the FCP for ALL commands, whether or not they have a directory prefix.
Since commands processed by the FCP have not been subjected to the command
processor loader, the external command FCB is still intact from the original
parse.  Consequently, the drive byte can be used to determine whether or not
a directory prefix was included with the command.  This technique is used to
advantage in Z33FCP.  If the invocation of IF, OR, or AND had a directory
specification (including a lone colon), then the FCP module immediately
loads the transient flow processor IF.COM, without first checking to see if
the requested option is supported in the resident code.  Thus a leading
colon can force the more powerful transient flow processor to be run, and
the code required to detect this request in the FCP module is minimal.