BIT DATA FORMAT
---------------
INPUT
    bits:       abc
    nibble:     jklm
    read:       pqrstuvw


    NEED    NIB BIT READ    RESULT      NIB BIT
    8       *   *   Y       pqrstuvw    

MODE DATA STRUCTURES
--------------------


COMMON
    BYTE    BITS    USAGE
    0       6-7                 type of mode: 0=menu 1=text 2=entry 3=func
    0       0-5                 byte count of entire mode (including this byte)


TEXT                                    40
    #ofBits     USAGE
    8           common
    8           # lines-1
    15          first string        NOTE: hi bit of nextmode is in hi bit of str
    9           next mode



MENU                                    00
    #ofBits     USAGE
    8           common
    8           # menu items
    16          title string (others follow title string)
    9           next mode 0
    9           next mode 1
                ...


ENTRY
    #ofBits     USAGE
    8           common                  80
    4           mask    (upper|lower|digit|space)
    4           prompt string
    8           function index
    8           parm0 (optional)
    8           parm1 (optional)
                ...


FUNC
    #ofBits     USAGE
    8           common                  c0
    8           function index
    8           parm0 (optional)
    8           parm1 (optional)
                ...


NEXT MODE FORMAT
0       = POP
N       = (N = 1-255) PUSH mode N
512+N   = (N = 1-255) SET  mode N




STRING FORMATS
--------------

    ALPHA MODE (default) - 5 bits
        0-25        a-z
        26          space
        27          ->caps
        28          ->alpha
        29          ->num
        30          special follows
        31          8 bit ASCII char follows


    CAPS MODE - 5 bits
        0-25        A-Z
        26          space
        27          ->caps
        28          ->alpha
        29          ->num
        30          special follows
        31          8 bit ASCII char follows


    NUM MODE - 4 bits
        0-9         0-9
        10          space
        11          ->caps
        12          ->alpha
        13          ->num
        14          special follows
        15          8 bit ASCII char follows



SPECIAL STRING CHARS

    CODE    PARM(BITS)  DESCIP
            -           clear screen
            -           backspace
            -           cursor on
            -           cursor off
            -           ir look
            char(8)     graphic character
            -           game time
            -           real time
            -           current clue title
            -           current clue time elapsed
            -           
    


CHARACTER DEFINITION
    ; this causes char to be defined AND displayed at current cursor loc

    28 bits total
    SIZE        DESCRIP
    3           which char to use
    5           pixels
    5           pixels
    5           pixels
    5           pixels
    5           pixels



CODE FORMAT
-----------
    BITS        DESC
    4           length of code (characters)
    
    N*6         code characters
    1           function parm
    1           function index


CONVERTING A STRING TO A CODE NUMBER:



int filter(int c)
{
    A-K ==> 0-10
    L   ==> 9       (same as I)
    M-Z ==> 11-24
    0   ==> 13      (same as O)
    1   ==> 9       (same as I)
    2-9 ==> 25-32

    c = toupper(c);
    ASSERT(isdigit(c) || isupper(c));
    c -= 'A'

}

int convert(char *code)
{
    char *s = code
    int num = 0;
    for (; *s; s++) {
        if (*s != A-Z0-9) continue
        num *= 33;
        num += filer(*s);
    }
    return num;
}


GET NEXT CODE NUMBER
6 digit codes:
MAX = 33^6 = 1291467969 = 0x4cfa3cc1
ADD = 0x0632d80f

int inc_code(int num)
{
    num = swap_each_nibble_pair(num)
    num += ADD;
    num %= MAX
}