1 = Open Adventure Maintainer's Notes =
4 In which we explain what has been done to this code since Don Woods
5 authorized us to ship it under an open-source license. There's a
6 separate link:history.html[history] describing how it came to us.
10 The principal maintainers of this code are Eric S. Raymond and Jason
11 Ninneman. Eric received Don Woods's encouragement to update and ship
12 the game; Jason signed on early in the process to help. The assistance
13 of Peje Nilsson in restructuring some particularly grotty gotos is
14 gratefully acknowledged. Petr Voropaev contributed fuzz testing and
15 code cleanups. Aaron Traas did a lot of painstaking work to improve
20 This project is called "Open Adventure" because it's not at all clear
21 to number Adventure past 2.5 without misleading or causing
22 collisions. Various of the non-mainline versions have claimed to be
23 versions 3, 4, 5, 6, 7 and for all I know higher than that. It seems
24 best just to start a new numbering series while acknowledging the
27 We have reverted to "advent" for the binary to avoid a name collision
28 with the BSD Games version.
32 Extreme care has been taken not to make changes that would alter the
33 logic of the game as we received it from Don Woods, except to fix
34 glitches that were clearly bugs. By policy, all user-visible
35 changes to gameplay must be revertible with the -o (oldstyle) option.
37 It is a goal of this project to exactly preserve the *intended
38 behavior* of 430-point Adventure, but the implementation of it is fair
39 game for improvement. In particular, we are concerned to move it to a
40 form that is (a) readable, and (b) friendly to forward translation to
41 future languages. It has already survived a move from FORTRAN to C; a
42 future as a Python or Go translation seems possible, even probable.
44 == Functional changes ==
48 * Reading the relocated Witt's End sign in the endgame didn't work right.
50 * Behavior when saying the giant's magic words outside his room wasn't
51 quite correct - the game responded as though the player were in
52 the room ("...can't you read?"). The new message is "Well, that was
53 remarkably pointless."
55 * Attempting to extinguish an unlit urn caused it to lose its oil.
57 * "A crystal bridge now spans the fissure." (progressive present) was
58 incorrect most places it appeared and has been replaced by "A crystal
59 bridge spans the fissure." (timeless present).
61 By default, advent issues "> " as a command prompt. This feature
62 became common in many variants after the original 350-point version,
63 but was never backported into Crowther & Woods's main line before now.
64 The "-o" (oldstyle) option reverts the behavior.
66 There is a set of standard one-letter command aliases conventional in modern
67 text adventure games; 'l' and 'x'; for 'look' (or 'examine'), 'z' to do nothing
68 for a turn, 'i' for 'inventory', 'g' for 'get', and 'd' for 'drop'. The 'd'
69 alias collides with 'd' for 'down', but the others have been implemented.
70 The "-o" (oldstyle) option disables them.
72 Unrecognized words are no longer truncated to 5 characters and
73 uppercased when they are echoed. The "-o" (oldstyle) option restores
76 A "seed" command has been added. This is not intended for human use
77 but as a way for game logs to set the PRNG (pseudorandom-number generator) so
78 that random events (dwarf & pirate appearances, the bird's magic word)
81 A -l command-line option has been added. When this is given (with a
82 file path argument) each command entered will be logged to the
83 specified file. Additionally, a generated "seed" command will be put
84 early in the file capturing the randomized start state of the PRNG
85 so that replays of the log will be reproducible.
87 Using "seed" and -l, the distribution now includes a regression-test
88 suite for the game. Any log captured with -l (and thus containing
89 a "seed" command) will replay reliably, including random events.
91 The adventure.text file is no longer required at runtime. Instead, an
92 adventure.yaml file is compiled at build time to a source module
93 containing C structures, which is then linked to the advent
94 binary. The YAML is drastically easier to read and edit than
95 the old ad-hoc format of adventure.txt.
97 The game-save format has changed. This was done to simplify the
98 FORTRAN-derived code that formerly implemented the save/restore
99 functions; without C's fread(3)/fwrite() and structs it was
100 necessarily pretty ugly by modern standards. Encryption and
101 checksumming have been discarded - it's pointless to try
102 tamper-proofing saves when everyone has the source code.
104 A -r command-line option has been added. When it is given (with a file
105 path argument) it is functionally equivalent to a RESTORE command.
109 The 2.5 code was a mechanical C translation of a FORTRAN original.
110 There were gotos everywhere and the code was, though functional,
111 ugly and quite unreadable.
113 Jason Ninneman and I have moved it to what is almost, but not quite,
114 idiomatic modern C. We refactored the right way, checking correctness
115 against a comprehensive test suite that we built first and verified
116 with coverage tools (we have over 98% coverage, with the remaining
117 confined to exception cases that are very difficult to reach). This is
118 what you are running when you do "make check".
120 The move to modern C entailed some structural changes. The most
121 important was the refactoring of over 350 gotos into if/loop/break
122 structures. We also abolished almost all shared globals; the main one
123 left is a struct holding the game's saveable/restorable state.
125 The original code was greatly complicated by a kind of bit-packing
126 that was performed because the FORTRAN it was written in had no string
127 type. Text from the adventure.text file was compiled into sequences
128 of sixbit code points in a restricted character set, packed 5 to a
129 32-bit word (it seems clear from the code that words were originally
130 *6* chars each packed into a PDP-10 36-bit word). A command noun or
131 verb was one of these words, and what would be string operations in a
132 more recent language were all done on sequences of these words.
134 We have removed all this bit-packing cruft in favor of proper C
135 strings. C strings may be a weak and leaky abstraction, but this is
136 one of the rare cases in which they are an obvious improvement over
137 what they're displacing...
139 We have also conducted extensive fuzz testing on the game using
140 afl (American Fuzzy Lop). We've found and fixed some crashers in
141 our new code (which occasionally uses malloc(3)), but none as yet
142 in Don's old code (which didn't).
144 The code falls short of being fully modern C in the following
147 * We have not attempted to translate the old code to pointer-based
148 idioms (as opposed, in particular, to integer-based array indexing).
149 We don't need whatever minor performance gains this might collect,
150 and the choice to refrain will make forward translation into future
153 * There are a few gotos left that resist restructuring; all are in the
154 principal command interpreter function implementing its state
157 * Linked lists (for objects at a location) are implemented using an array
158 of link indices. This is a surviving FORTRANism that is quite unlike
159 normal practice in C or any more modern language. We have not tried
160 to fix it because doing so would (a) be quite difficult, and (b)
161 compromise forward-portability to other languages.
163 * Much of the code still assumes one-origin array indexing. Thus,
164 arrays are a cell larger than they strictly need to be and cell 0 is
167 * The code is still mostly typeless, slinging around machine longs
168 like a FORTRAN or BCPL program. Some (incomplete) effort has been made
169 to introduce semantic types.
171 We have made exactly one minor architectural change. In addition to the
172 old code's per-object state-description messages, we now have a per-object
173 message series for state *changes*. This makes it possible to pull a fair
174 amount of text out of the arbitrary-messages list and associate those
175 mesages with the objects that conceptually own them.