I remember when I was a kid I used to love playing Joe Power’s “Wizard’s Castle” game, which is about 900 lines and, as I learned today, originally ran on the 16-kilobyte model of the Exidy Sorcerer home computer at the New Directions in Computing computer store, after which the Kingdom of N’Dic is named.
When I was a kid I tried to understand the source code of the game, since after all it is only 900 lines, written in a programming language I was pretty familiar with, and performed a function I was pretty familiar with, having spent hundreds, if not thousands, of hours playing the game. Unfortunately, I didn’t know what I was looking for.
I just downloaded the IPCO version of the the game from myabandonware.com and find that it’s still somewhat hard to understand the source. Unfortunately this version is broken, or rather cheated — the map is revealed starting from the beginning of the game. So I needed to fix the bug, which turned out to be that line 4150 said:
4150 IF Q > 99 THEN Q=Q-100 ' LET Q=34 TO HIDE ROOMS
when it should say:
4150 IF Q > 99 THEN Q=34 ' LET Q=34 TO HIDE ROOMS
It also has a bug on line 3590, which says:
3590 PRINT CHR$(27);"E"
This is the clear-screen sequence for the Heath H89 and H19, but this version of the program is for GW-BASIC or BASICA; this line should just say
3590 CLS
Here is a sort of dictionary of the subroutines, goto targets, and variables in the program.
A$: a temporary input variable.
Q: a temporary variable used in many places for many things.
R$: an array of the 4 player race names. RC: the index of the player’s race.
SAMP$: a parameter indicating whether the program was invoked from IPCO's SAMPLES.BAS program; if "YES" (due to being invoked as CHAIN "WIZARD", 1010) then, upon exit, it reinvokes SAMPLES.BAS rather than exiting to the BASIC prompt.
1000: program entry point
RF: a boolean indicating whether you have the Runestaff OF: a boolean indicating whether you have the Orb of Zot
L: an array of 512 ints, representing the castle contents. For whatever reason (perhaps resulting from the conversion from the Sorceror version which stored this array in character RAM), this is a one-dimensional array with indices calculated by FND(Z) rather than a three-dimensional array. L entries have 100 added to them to mark them as “unknown”. Valid numbers range from 1–33 and 101–133, with 34 as a sort of special case representation of the whole 101–133 range for the map.
The valid values are:
These are used to index into C$() and I$() mentioned below.
The two other special unique items (the Runestaff and the Orb of Zot) do not have their own codes; the Runestaff is in the possession of a monster (and is thus in the same room with it) while the Orb of Zot is “disguised as” a warp, and in fact behaves as one.
C$(): an array of the 34 strings describing different room contents; the 34th is the dummy entry "X".
I$(): an array of the 34 characters to display different room contents on the map.
9590–9620: a subroutine to pick a randomly chosen empty room and set its contents to Q, returning its results in X, Y, and Z.
C: a 3×4 array of ints. C(1,4), C(2,4), and C(3,4) are used to represent whether the player is afflicted with particular curses, I think — a leech that drains your gold, lethargy that makes you move more slowly, and forgetfulness, which slowly erases your map. These curses are found in particular empty rooms. This logic is in lines 2940–3050.
Lethargy apparently just makes you eat more often, but not eating doesn’t harm you. This has the feeling of an unfinished feature. However, lethargy also gives monsters the initiative in combat.
H: the last time you ate. T: The current time.
W$(): an array of weapon and armor names; NO WEAPON is index 1, while NO ARMOR is index 5.
E$(): an array of 8 dishes one can cook from monsters.
WV: one less than the index of your current weapon in W$(), or 0 if you are empty-handed.
AV: 5 less than the index of our current armor in W$(), or 0 if you are empty-handed. AH: your armor’s health or armor’s hit points; when this reaches 0, the armor is destroyed.
LF: 1 if the player has a lamp, 0 otherwise. FL: the number of flares the player has. BL: 1 if the player is blind, 0 otherwise. BF: 1 if the player has a book stuck to their hands, 0 otherwise.
T(): an array of 8 ints which are 1 if the player possesses the corresponding treasure or 0 otherwise. These are in the same order as the numbers for the room contents; for valid indices, T(Q) represents the possession of C$(Q+25).
O(): an array of 3 ints containing the coordinates of the Orb of Zot R(): an array of 3 ints containing the coordinates of the Runestaff
O$: the returned user input from the subroutine at 9830 or other input subroutines
FNA(Q): returns a random number in [1, Q]
FNB(Q): returns Q wrapped to the range [1, 8] (i.e. (Q-1) % 8 + 1), which is what you want for wrapping coordinates to the 3×3×3 hypertorus structure of Zot’s castle
FNC(Q): returns Q if Q<19, otherwise 18; used for saturating arithmetic on character attribute values (strength ST, dexterity DX, intelligence IQ), which cannot increase past 18.
FND(Z): returns the index into L at which to find the contents of castle room (X, Y, Z).
FNE(Q): returns, roughly, Q % 100 — used to compute the true contents of a possibly unmapped room.
X: an X-coordinate in the castle, normally that of the player (but also an implicit argument to FND); saved in A when a temporary value is needed
Y: a Y-coordinate in the castle, normally that of the player (but also an implicit argument to FND); saved in B when a temporary value is needed
Z: a Z-coordinate in the castle, normally that of the player; saved in C when a temporary value is needed
A, B, C: used to save the player’s X, Y, and Z at times; also used in one place temporarily for the coordinates of the Orb of Zot. Also, during combat, A is used to store the index of the monster type (12 less than its index into C$().)
VF: 1 if vendors are angry with you, 0 otherwise
Y$: a prompt string
NG: the number of games played so far, used to avoid reintroducing the game
1–1200: initialization code for the whole program
1240–1390: initialization code for a new game (“restocking the castle”)
9770–9820: subroutine to print a line of asterisks
9830–9870: subroutine to request a generic one-letter choice from the user in O$, with two entry points — the entry point at 9830 prints a blank line and a prompt, while the entry point at 9850 does not.
2920–8410: the main game turn loop.