macro get_last_dot_position pos*, [str*] {
common
local c
    virtual at 0
        db str
        repeat $
            load c from $-%
            if c = '.'
                pos = $-%
                break
            end if
        end repeat
    end virtual
}

macro db_to pos*, [str*] {
common
local c
    repeat pos
        virtual at 0
            db str
            load c from %-1
        end virtual
        db c
    end repeat
}

macro db_from pos*, [str*] {
common
local c, len
    virtual at 0
        db str
        len = $
    end virtual
    repeat len-(pos)
        virtual at 0
            db str
            load c from pos+%-1
        end virtual
        db c
    end repeat
}

macro upcase pstr*, len* {
local c
    repeat len
        load c from pstr+%-1
        if c >= 'a' & c <= 'z'
            store c-'a'+'A' at pstr+%-1
        end if
    end repeat
}

macro build_8.3_name [name*] {
local pos, off
    get_last_dot_position pos, name
    off = $
    db_to pos, name
    upcase off, $-off
    if off+8>$
        db off+8-$ dup ' '
    end if
    off = $
    db_from pos+1, name
    upcase off, $-off
    if off+3>$
        db off+3-$ dup ' '
    end if
}


build_8.3_name "io.sys", "msdos.sys", "command.com"