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Function 29h            Parse Filename

    Converts a filename string on the form drive:filename.extension
    into a string of the form required for a file control block (FCB).

    This function is useful primarily when FCBs are used; it cannot be
    used with file specifications which include a path (directory).

        Entry   AH    = 29h
                AL    = Parse control mask
                DS:SI = Pointer to a series of d:filename.ext strings
                        (? * allowed)
                ES:DI = Pointer to an FCB structure

        Return  AL    = 00h   No wildcards found in filename.ext
                        01h   One or more wildcards in filename.ext
                        0FFh  Function failed (invalid drive letter)
                DS:SI = Pointer to first un-parsed character
                FCB structure modified, unless the parse control mask
                specifies otherwise (ES and DI are unchanged)
                        If the string at DS:SI does not contain a
                        valid filename, FCB.fcbFileName (byte at
                        ES:DI+1) contains a space character

    ------------------------------------------------------------------

    The parse control mask (in AL) controls how DOS parses the string
    at DS:SI:

        Bit     Meaning
        0       0 = Stops parsing if a filename separator is
                    encountered
                1 = Ignores leading separators

        1       If the string does not contain a drive letter
                0 = sets FCB.fcbDriveID to 00h (default drive)
                1 = leaves FCB.fcbDriveID unchanged

        2       If the string does not contain a filename
                0 = sets FCB.fcbFileName to 8 spaces
                1 = leaves FCB.fcbFileName unchanged

        3       If the string does not contain a file extension
                0 = sets FCB.fcbExtent to 3 spaces
                1 = leaves FCB.fcbExtent unchanged (a default
                    file extension, for example)

        4-7     Reserved (0)

    ------------------------------------------------------------------

    This function fills the fcbDriveID, fcbFileName, and fcbExtent
    fields of the specified FCB structure unless the parse control
    mask (passed in AL) specifies otherwise. To fill these fields, the
    function strips any leading white-space characters (spaces and
    tabs) from the string pointed to by DS:SI, then uses the remaining
    characters to create the drive number, filename, and filename
    extension. If bit 0 in the parse control mask is set, the function
    also strips exactly one filename separator if one appears before
    the first non-white-space character (SI advanced by 1). The
    following are valid filename separators: :.;,=+

    Once the function begins to convert a filename, it continues to
    read characters from the string until it encounters a white-space
    character, a filename separator, a control character (ASCII 00h
    through 1Fh), or one of the following characters: /"[]<>|

    ------------------------------------------------------------------

    If the filename in the string has fewer than 8 characters, the
    function fills the remaining bytes in the fcbFileName field with
    spaces. If the filename extension has fewer than 3 characters, the
    function fills the remaining bytes in the fcbExtent field with
    spaces.

    If an "*" wildcard character is encountered in the filename or
    extension, the function fills out the remaining bytes in the
    fcbFileName or fcbFileExtent fields with "?" wildcard characters.