Source Comparison: Repository Code vs. Known Hack Variants

This document compares the source code in original/ against all three known derivatives of Jay Fenlason's Hack plus Andries Brouwer's Hack 1.0.

Sources compared:

Label	Location	Origin
Repo	`original/`	This repository
PDP-11	`hack-pdp11/src/`	Usenet shar, Michiel Huisjes, VU Amsterdam, Feb 1985
PC/IX	`pcix/src/`	Usenet shar, "peterb at pbear", May 1985
Hack 1.0	`hack-v1.0/ab_hack-1.0/`	Andries Brouwer, posted to Usenet Dec 1984

hack121 (DOS binary, no source extant) is referenced from the NetHack Wiki bestiary tables where applicable.

1. Monster Table

The main monster table is an 8x7 array (struct permonst mon[8][7]). Levels 1--4 are nearly identical across all variants. Divergence begins at level 5.

Levels 1--4 (shared across all variants with D&D names)

All four source variants use the same monsters and stats for levels 1--4. Minor spelling differences exist (repo has "homonculous" and "gelatenous").

Repo: original/hack.vars:57-87
PDP-11: hack-pdp11/src/hack.monst.c:34-65
PC/IX: pcix/src/hack.monst.c:34-65
Hack 1.0: hack-v1.0/ab_hack-1.0/hack.monst.c:7-34

Level 5+ divergences

Slot	Repo (`original/hack.vars`)	PDP-11 / PC/IX	Hack 1.0
5.3	rust monster R 5hd `:77`	rust monster R 5hd	rust monster R 10hd
5.4	giant scorpion s `:78`	giant scorpion s	scorpion s
5.5	teleporter t `:79`	teleporter t	tengu t
5.7	yeti Y `:95`	long worm w	long worm w (or wumpus w under `NOWORM`)
6.1	displacer beast d `:97`	large dog d	large dog d
6.6	ugod u `:102`	ugod u	unicorn u
6.7	xerp x `:103`	yeti Y	yeti Y
7.4	wumpus w `:108`	xorn X	xorn X
7.5	xorn X `:109`	xerp x	xan x
7.6	zelomp z `:110`	zelomp z	zruty z
8.1	dragon D 10hd `:113`	dragon D 20hd	dragon D 10hd
8.3	lurker above ~ `:115`	lurker above '	lurker above ~
8.4	neo-otyugh n `:116`	neo-otyugh n	nurse n
8.6	purple worm P 15hd `:118`	purple worm P 20hd	purple worm P 15hd
8.7	demon & 10hd `:119`	demon & 14hd	demon & 10hd

Key observations:

Displacer beast (original/hack.vars:97): Present only in the repo. Absent from PDP-11, PC/IX, Hack 1.0, and hack121. Occupies the 'd' slot that all other variants assign to large dog (needed for pet system).
Wumpus (original/hack.vars:108): Present in the repo and in hack121. Absent from PDP-11 and PC/IX. In Hack 1.0, wumpus exists only as a fallback when the worm system is disabled: hack-v1.0/ab_hack-1.0/hack.monst.c:41-45:
```
#ifdef NOWORM
    { "wumpus",    'w',8,3,2,3,6,0 },
#else
    { "long worm", 'w',8,3,5,1,4,0 },
#endif NOWORM
```
This confirms wumpus was in whatever code Brouwer started from and was replaced when the worm system was added.
Hit dice: The repo matches Hack 1.0 for dragon (10hd), purple worm (15hd), and demon (10hd). PDP-11 and PC/IX inflate these to 20, 20, and 14 respectively.
Lurker above symbol: Repo uses ~ (original/hack.vars:115), matching Hack 1.0 (hack.monst.c:61). PDP-11 and PC/IX use '.

Monsters in separate structures

Repo	PDP-11 / PC/IX	Hack 1.0
vampire bat (`original/hack.vars:124`)	li_dog, dog, la_dog, shk, treasurer, ghost, eel	li_dog, dog, la_dog, shopkeeper

The repo has only the vampire bat in a separate struct. All other variants have full dog/pet hierarchies and shopkeeper definitions.

Monster count

Repo: 56 (8x7 main) + 1 (vampire bat) = 57
PDP-11: 56 + shopkeeper, treasurer, li_dog, dog, la_dog, ghost, eel = 63+
PC/IX: same as PDP-11
Hack 1.0: 58 (main, including shopkeeper and minotaur appended) + li_dog, dog, la_dog = 61

2. Amulet

Variant	Name	Reference
Repo	Amulet of Frobozz	`original/hack.c:394`, `original/exp/exp1/hack.obj.c:10`
PDP-11	Amulet of Frobozz	`hack-pdp11/src/hack.c:228`, `hack-pdp11/src/show.c:283`
PC/IX	Amulet of Frobozz	`pcix/src/hack.c:228`, `pcix/src/show.c:284`
Hack 1.0	Amulet of Yendor	`hack-v1.0/ab_hack-1.0/hack.objnam.c:46`, `def.objects.h:11`
hack121	(not documented)	(binary only, no source)

PDP-11 help text also contains a third name, "Amulet of Guyver" (hack-pdp11/src/help:4), inconsistent with its own code.

3. Potions

Slot	Repo (`original/hack.vars:172-188`)	PDP-11	PC/IX (`pcix/src/hack.vars.h:29-45`)	Hack 1.0
1	restore strength	restore strength	restore strength	restore strength
2	alcohol	booze	confuse monster	booze
3	invisibility	invisibility	invisibility	invisibility
4	fruit juice	fruit juice	fruit juice	fruit juice
5	healing	healing	healing	healing
6	paralysis	paralysis	paralysis	paralysis
7	monster detection	monster detection	monster detection	monster detection
8	object detection	object detection	object detection	object detection
9	sickness	sickness	sickness	sickness
10	confusion	confusion	confusion	confusion
11	gain strength	gain strength	gain strength	gain strength
12	speed	speed	speed	speed
13	blindness	blindness	blindness	blindness
14	gain level	gain level	gain level	gain level
15	extra healing	extra healing	extra healing	extra healing
16	--	--	--	levitation

The repo's "alcohol" (original/hack.vars:174) is unique among extant source variants. PDP-11 and Hack 1.0 use "booze". PC/IX replaced booze with "confuse monster" (per wiki, reinstating confuse monster as a potion after PDP-11 removed the scroll).

4. Scrolls

Slot	Repo (`original/hack.vars:207-223`)	PDP-11 / PC/IX (`pcix/src/hack.vars.h:75-91`)	Hack 1.0
1	enchant armor	enchant armor	enchant armor
2	confuse monster	losing (S_DROP)	confuse monster
3	blank	curse levels (S_CURSE_LEV)	(blank paper, different position)
4	remove curse	remove curse	remove curse
5	enchant weapon	enchant weapon	enchant weapon
6	create monster	create monster	create monster
7	damage weapon	damage weapon	damage weapon
8	rust armor	genocide	destroy armor
9	genocide	destroy armor (S_DESTR_ARMOR)	genocide
10	light	light	light
11	teleportation	transportation (elevator)	teleportation
12	gold detection	gold detection	gold detection
13	identify	identify	identify
14	magic mapping	magic mapping	magic mapping
15	fire	fire	fire

confuse monster (original/hack.vars:209): Repo and Hack 1.0 retain it. PDP-11 and PC/IX replaced it with "losing" (S_DROP), documented in hack-pdp11/src/hack.do.c:69-73:
```
/* New scroll instead of scroll of monster confusion. This scroll
 * drops everything you have on you. And put it somewhere on the level
 * Michiel and Fred */
```
rust armor (original/hack.vars:215): Unique to the repo. All other variants with extant source use "destroy armor".
teleportation (original/hack.vars:218): Repo and Hack 1.0 use simple teleportation. PDP-11/PC/IX changed it to an elevator with level-jumping (hack-pdp11/src/hack.do.c:195-198):
```
/* Extended by Michiel and Fred:
 * One can jump between levels */
```

5. Wands

Repo (`original/hack.vars:243-268`)	PDP-11 / PC/IX (`pcix/src/hack.vars.h:117-136`)	Hack 1.0
light	light	light
secret door + trap detection	secret door + trap detection	secret door detection
create monster	create monster	create monster
striking	exhaustion	striking
slow monster	slow monster	slow monster
speed monster	speed monster	speed monster
undead turning	undead turning	undead turning
polymorph	polymorph	polymorph
cancelation	cancellation	cancellation
teleport monster	teleport monster	teleport monster
digging	digging	digging
magic missile	magic missile	magic missile
fire	fire	fire
sleep	sleep	sleep
cold	cold	cold
death	death	death
--	confusion	--
--	door closing	--
--	--	wishing
--	--	make invisible

The repo retains "striking" (original/hack.vars:251), matching Hack 1.0. PDP-11/PC/IX replaced it with "exhaustion".

The repo lacks wands of confusion and door closing (VU Amsterdam additions) and wands of wishing and make invisible (Brouwer additions).

6. Rings

The repo defines 17 ring types (original/hack.vars:288-306). PDP-11/PC/IX define 16. The difference:

increase hit points (original/hack.vars:305): Present in the repo and hack121. Absent from PDP-11/PC/IX.

7. Food

Repo (`original/hack.vars:146-149`)	PDP-11 / PC/IX	Hack 1.0
food ration	food ration	food ration
fruit	tripe ration	tripe ration
--	pancake	pancake
--	dead lizard	dead lizard
--	cookie	fortune cookie
--	orange	orange
--	apple	apple
--	pear	pear
--	melon	melon
--	banana	banana
--	candy bar	candy bar
--	egg	egg
--	--	carrot
--	--	tin
--	--	clove of garlic
--	--	corpse

The repo has 2 food types. PDP-11/PC/IX have 12. Hack 1.0 has 16.

8. Armor

Repo (`original/hack.vars:138-145`)	PDP-11 / PC/IX	Hack 1.0
leather (AC 8)	leather armor	leather armor
ring (AC 7)	ring mail	ring mail
scale (AC 6)	scale mail	scale mail
chain (AC 5)	chain mail	chain mail
splint (AC 4)	splint mail	splint mail
plate (AC 3)	plate mail	plate mail
--	banded mail	banded mail
--	studded leather armor	studded leather armor
--	elven cloak	elven cloak
--	--	helmet
--	--	shield
--	--	pair of gloves

The repo has 6 armor types (suits only). PDP-11/PC/IX have 9. Hack 1.0 has 12.

9. Game Systems Absent from Repo

The following systems are present in PDP-11, PC/IX, and/or Hack 1.0 but entirely absent from the repo:

Pet / dog system

PDP-11/PC/IX define three dog types and a full movement AI:

hack-pdp11/src/hack.monst.c:101-103 (li_dog, dog, la_dog)
hack-pdp11/src/hack.mon.do.c:468-469 (dog_move dispatch)
hack-pdp11/src/hack.h:218 (mtame bit field in struct monst)

Hack 1.0: hack-v1.0/ab_hack-1.0/hack.dog.c (entire file, 400+ lines)

Brouwer's own README confirms this was his addition: hack-v1.0/ab_hack-1.0/READ_ME:11-12:

"The current version is more than twice as large (with such new features as the dog, the long worms, the shops, etc.) and almost entirely rewritten"

The repo's struct monst (original/hack.h:70-82) has no mtame, angry, ale, wormno, or mxlth fields.

Worm segment system

PDP-11/PC/IX: struct wseg at hack-pdp11/src/hack.h:231-234, worm functions throughout.

Hack 1.0: hack-v1.0/ab_hack-1.0/hack.worm.c (entire file), def.wseg.h.

Not present in the repo. The repo uses yeti in the slot PDP-11/PC/IX assign to long worm, and wumpus in a slot where other variants have xorn. Hack 1.0's #ifdef NOWORM conditional (hack.monst.c:41-45) confirms wumpus was the original monster before the worm system existed.

Special room types

PDP-11/PC/IX define and generate four special room types:

mkzoo(): hack-pdp11/src/mklev.make.c:275, pcix/src/mklev.make.c:275
mkyard() (graveyard): hack-pdp11/src/mklev.make.c:297, pcix/src/mklev.make.c:297
mkswamp(): hack-pdp11/src/mklev.make.c:397, pcix/src/mklev.make.c:397
mk_knox() (vault): hack-pdp11/src/mklev.make.c:450, pcix/src/mklev.make.c:450

Hack 1.0 has shops (mklv.shk.c), vaults (hack.vault.c), and zoos.

The VU Amsterdam developers documented these as their own additions in the PDP-11 Hack readme (hack-pdp11/src/READ_ME:33-41):

"Some additions we (Fred de Wilde and Michiel Huisjes) made are

The Vault / - The Swamp / - The Zoo / - The Graveyard"

The repo has none of these. Its mklev.c generates only basic rooms, corridors, and mazes.

MAXLEVEL

PDP-11/PC/IX: #define MAXLEVEL 40 (hack-pdp11/src/hack.save.c:15, pcix/src/hack.do.misc.c:14).

Not defined in the repo.

Pool / water locations

PDP-11/PC/IX: #define POOL 7 (hack-pdp11/src/hack.h:42), with ale (aquatic) monster support.

Not present in the repo. The repo's original/hack.h:7-11 defines location types WALL through ROOM only.

10. Structural Differences

struct monst

Field	Repo (`original/hack.h:70-82`)	PDP-11 (`hack-pdp11/src/hack.h:202-222`)	Hack 1.0 (`def.monst.h`)
nmon	yes	yes	yes
mx, my	yes	yes	yes
mhp, orig_hp	yes (char)	yes (int)	yes (int)
invis	yes	yes	yes
cham	yes	yes	yes
mspeed	yes	yes	yes
mcan	yes	yes	yes
mstuck	yes	--	--
sinv	yes	--	--
mstat	yes (2 bits)	--	--
angry	--	yes	yes
ale	--	yes	--
msleep	--	yes (bit)	yes
mfroz	--	yes (bit)	yes
mconf	--	yes (bit)	yes
mflee	--	yes (bit)	yes
mtame	--	yes (bit)	yes
wormno	--	yes (5 bits)	yes
mxlth	--	yes	yes
mextra	--	yes	yes

The repo's struct is notably simpler. It uses a combined mstat field (2 bits for flee/sleep/frozen) rather than separate bit fields. It includes sinv and mstuck fields not present in other variants.

struct obj

The repo's struct obj (original/hack.h:101-110) lacks the unpaid field present in PDP-11 (hack-pdp11/src/hack.h:188) and Hack 1.0 (for shop tracking).

struct you (player)

The repo (original/hack.h:134-164) lacks:

uinshop, uinzoo, uinyard, uinswamp, uinknox (PDP-11/PC/IX special room tracking)
uhcursed (PDP-11/PC/IX hero curse flag, tied to S_CURSE_LEV scroll)

11. README Comparison

Fenlason's README exists in three forms:

Location	Content
Repo `original/READ_ME`	11 setup steps, mentions MAGIC mode (gid==42), SMALL/VTONL paragraph
Hack 1.0 `Original_READ_ME`	9 setup steps (renumbered, "2.5"), no SMALL/VTONL paragraph
Hack 1.0 `READ_ME`	Brouwer's own, credits Fenlason "at lincolnsudbury"

All three credit the same collaborators: Kenny Woodland (KW), Mike Thome (MT), Jon Payne (JP), and reference the SFSU Logo Workshop and Mike Clancy.

Brouwer's README (hack-v1.0/ab_hack-1.0/READ_ME:6) identifies Fenlason's location as "lincolnsudbury" -- consistent with Lincoln-Sudbury Regional High School.

12. Scroll Name Strings

The scroll incantation strings provide a fingerprint. The repo (original/hack.vars:224-241) uses lowercase; PDP-11/PC/IX (pcix/src/hack.vars.h:94-111) use uppercase. Both share the same words in the same order, with one exception:

Repo	PDP-11 / PC/IX
"Velox Neb"	"VELOX NEB"
"Foobie Bletch"	"FOOBIE BLETCH"
"Temov"	"TEMOV"
"Garven Deh"	"GARVEN DEH"
"Zelgo Mer"	"ZELGO MER"
"Andova Begarin"	"ANDOVA BEGARIN"
"Elam Ebow"	"ELAM EBOW"
"Kernod Wel"	"KERNOD WEL"
"Tharr"	"THARR"
"Venzar Borgavve"	"VENZAR BORGAVVE"
"Elbib Yloh"	(commented out)
"Verr Yed Horre"	"VERR YED HORRE"
"Juyed Awk Yacc"	"JUYED AWK YACC"
"Hackem Muche"	"HACKEM MUCHE"
"Lep Gex Ven Zea"	"LEP GEX VEN ZEA"
"Daiyen Fooels"	"DAIYEN FOOELS"

"Elbib Yloh" ("Holy Bible" reversed) is present in the repo but commented out in PC/IX (pcix/src/hack.vars.h:105: /* "ELBIB YLOH", */).

13. Files Unique to This Repository

The repo contains files not present in any known Hack distribution:

original/.cshrc, original/.login, original/.exrc, original/.msgsrc -- Shell and editor configuration from a development environment. .login sets prompt to Hack: and references IBM terminal via term -c -M ibm.
original/zork/ -- Zork reference material (zork.h, dungeon.c), likely used as design reference during Hack development.
original/exp/ and original/exp/exp1/ -- Development branches showing code evolution. exp/exp1/ contains a modularized refactoring splitting code into fight, move, screen, and object subsystems (~4600 lines). exp/exp1/bugs1 contains V7 lint output.
original/record -- High score table with entries from users "karll", "nike", "shm", "jaws", "thm", "adam", and "Jay the Hacker" (original/record:9). Jay's entry shows death by "Bus error" (SIGBUS crash).

14. Summary of Unique Features

Features present only in the repo (not in any variant with extant source):

Feature	Reference
Displacer beast monster	`original/hack.vars:97`
"alcohol" potion (not "booze")	`original/hack.vars:174`
"rust armor" scroll (not "destroy armor")	`original/hack.vars:215`
2-item food list (food ration, fruit)	`original/hack.vars:146-149`
6-type armor list (suits only)	`original/hack.vars:138-145`
`sinv` and `mstuck` fields in struct monst	`original/hack.h:73,79`
Combined `mstat` field (2-bit)	`original/hack.h:77`
"Elbib Yloh" scroll name (uncommented)	`original/hack.vars:235`
Personal dev environment files	`original/.cshrc`, `original/.login`, `original/.exrc`
Zork reference material	`original/zork/`
Experimental refactoring branches	`original/exp/`, `original/exp/exp1/`

Features the repo shares with Hack 1.0 but not PDP-11/PC/IX:

Feature	Repo	Hack 1.0
Wumpus monster	`original/hack.vars:108`	`hack.monst.c:42` (under `NOWORM`)
Dragon 10hd	`original/hack.vars:113`	`hack.monst.c:59`
Demon 10hd	`original/hack.vars:119`	`hack.monst.c:65`
Purple worm 15hd	`original/hack.vars:118`	`hack.monst.c:64`
Lurker above ~	`original/hack.vars:115`	`hack.monst.c:61`
Wand of striking	`original/hack.vars:251`	`def.objects.h:209`
Scroll of confuse monster	`original/hack.vars:209`	`def.objects.h:179`
Scroll of teleportation (simple)	`original/hack.vars:218`	(same name)

Features the repo shares with hack121 (DOS binary, per NetHack Wiki) but not PDP-11/PC/IX:

Wumpus monster
Ring of increase hit points (original/hack.vars:305)
"alcohol" potion (hack121 also uses "alcohol")

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Source Comparison: Repository Code vs. Known Hack Variants

1. Monster Table

Levels 1--4 (shared across all variants with D&D names)

Level 5+ divergences

Monsters in separate structures

Monster count

2. Amulet

3. Potions

4. Scrolls

5. Wands

6. Rings

7. Food

8. Armor

9. Game Systems Absent from Repo

Pet / dog system

Worm segment system

Special room types

MAXLEVEL

Pool / water locations

10. Structural Differences

struct monst

struct obj

struct you (player)

11. README Comparison

12. Scroll Name Strings

13. Files Unique to This Repository

14. Summary of Unique Features

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Source Comparison: Repository Code vs. Known Hack Variants

1. Monster Table

Levels 1--4 (shared across all variants with D&D names)

Level 5+ divergences

Monsters in separate structures

Monster count

2. Amulet

3. Potions

4. Scrolls

5. Wands

6. Rings

7. Food

8. Armor

9. Game Systems Absent from Repo

Pet / dog system

Worm segment system

Special room types

MAXLEVEL

Pool / water locations

10. Structural Differences

struct monst

struct obj

struct you (player)

11. README Comparison

12. Scroll Name Strings

13. Files Unique to This Repository

14. Summary of Unique Features