In which we explain what has been done to this code since Don Woods authorized us to ship it under an open-source license. There’s a separate history describing how it came to us.

Who we are

The principal maintainers of this code are Eric S. Raymond and Jason Ninneman. Eric received Don Woods’s encouragement to update and ship the game; Jason signed on early in the process to help. The assistance of Peje Nilsson in restructuring some particularly grotty gotos is gratefully acknowledged. Petr Voropaev contributed fuzz testing and code cleanups. Aaron Traas did a lot of painstaking work to improve test coverage.

Nomenclature

This project is called "Open Adventure" because it’s not at all clear to number Adventure past 2.5 without misleading or causing collisions. Various of the non-mainline versions have claimed to be versions 3, 4, 5, 6, 7 and for all I know higher than that. It seems best just to start a new numbering series while acknowledging the links back.

We have reverted to "advent" for the binary to avoid a name collision with the BSD Games version.

Philosophy

Extreme care has been taken not to make changes that would alter the logic of the game as we received it from Don Woods, except to fix glitches that were clearly bugs. By policy, all user-visible changes to gameplay must be revertible with the -o (oldstyle) option.

It is a goal of this project to exactly preserve the intended behavior of 430-point Adventure, but the implementation of it is fair game for improvement. In particular, we are concerned to move it to a form that is (a) readable, and (b) friendly to forward translation to future languages. It has already survived a move from FORTRAN to C; a future as a Python or Go translation seems possible, even probable.

Functional changes

Bug fixes:

  • Reading the relocated Witt’s End sign in the endgame didn’t work right.

  • Behavior when saying the giant’s magic words outside his room wasn’t quite correct - the game responded as though the player were in the room ("…can’t you read?"). The new message is "Well, that was remarkably pointless."

  • Attempting to extinguish an unlit urn caused it to lose its oil.

  • "A crystal bridge now spans the fissure." (progressive present) was incorrect most places it appeared and has been replaced by "A crystal bridge spans the fissure." (timeless present).

  • Under odd circumstances (dropping rug or vase outdoors) the game could say "floor" when it should say "ground" (or "dirt", or something).

By default, advent issues "> " as a command prompt. This feature became common in many variants after the original 350-point version, but was never backported into Crowther & Woods’s main line before now. The "-o" (oldstyle) option reverts the behavior.

There is a set of standard one-letter command aliases conventional in modern text adventure games; l and x; for look (or examine), z to do nothing for a turn, i for inventory, g for get, and d for drop. The d alias collides with d for down, but the others have been implemented. The "-o" (oldstyle) option disables them.

Unrecognized words are no longer truncated to 5 characters and uppercased when they are echoed. The "-o" (oldstyle) option restores this behavior.

A "seed" command has been added. This is not intended for human use but as a way for game logs to set the PRNG (pseudorandom-number generator) so that random events (dwarf & pirate appearances, the bird’s magic word) will be reproducible.

A -l command-line option has been added. When this is given (with a file path argument) each command entered will be logged to the specified file. Additionally, a generated "seed" command will be put early in the file capturing the randomized start state of the PRNG so that replays of the log will be reproducible.

Using "seed" and -l, the distribution now includes a regression-test suite for the game. Any log captured with -l (and thus containing a "seed" command) will replay reliably, including random events.

The adventure.text file is no longer required at runtime. Instead, an adventure.yaml file is compiled at build time to a source module containing C structures, which is then linked to the advent binary. The YAML is drastically easier to read and edit than the old ad-hoc format of adventure.txt.

The game-save format has changed. This was done to simplify the FORTRAN-derived code that formerly implemented the save/restore functions; without C’s fread(3)/fwrite() and structs it was necessarily pretty ugly by modern standards. Encryption and checksumming have been discarded - it’s pointless to try tamper-proofing saves when everyone has the source code.

A -r command-line option has been added. When it is given (with a file path argument) it is functionally equivalent to a RESTORE command.

Translation

The 2.5 code was a mechanical C translation of a FORTRAN original. There were gotos everywhere and the code was, though functional, ugly and quite unreadable.

Jason Ninneman and I have moved it to what is almost, but not quite, idiomatic modern C. We refactored the right way, checking correctness against a comprehensive test suite that we built first and verified with coverage tools (there is effectively 100% code coverage). This is what you are running when you do "make check".

The move to modern C entailed some structural changes. The most important was the refactoring of over 350 gotos into if/loop/break structures. We also abolished almost all shared globals; the main one left is a struct holding the game’s saveable/restorable state.

The original code was greatly complicated by a kind of bit-packing that was performed because the FORTRAN it was written in had no string type. Text from the adventure.text file was compiled into sequences of sixbit code points in a restricted character set, packed 5 to a 32-bit word (it seems clear from the code that words were originally 6 chars each packed into a PDP-10 36-bit word). A command noun or verb was one of these words, and what would be string operations in a more recent language were all done on sequences of these words.

We have removed all this bit-packing cruft in favor of proper C strings. C strings may be a weak and leaky abstraction, but this is one of the rare cases in which they are an obvious improvement over what they’re displacing…

We have also conducted extensive fuzz testing on the game using afl (American Fuzzy Lop). We’ve found and fixed some crashers in our new code (which occasionally uses malloc(3)), but none as yet in Don’s old code (which didn’t).

The code falls short of being fully modern C in the following ways:

  • We have not attempted to translate the old code to pointer-based idioms (as opposed, in particular, to integer-based array indexing). We don’t need whatever minor performance gains this might collect, and the choice to refrain will make forward translation into future languages easier.

  • There are a few gotos left that resist restructuring; all are in the principal command interpreter function implementing its state machine.

  • Linked lists (for objects at a location) are implemented using an array of link indices. This is a surviving FORTRANism that is quite unlike normal practice in C or any more modern language. We have not tried to fix it because doing so would (a) be quite difficult, and (b) compromise forward-portability to other languages.

  • Much of the code still assumes one-origin array indexing. Thus, arrays are a cell larger than they strictly need to be and cell 0 is unused.

  • The code is still mostly typeless, slinging around machine longs like a FORTRAN or BCPL program. Some (incomplete) effort has been made to introduce semantic types.

We have made exactly one minor architectural change. In addition to the old code’s per-object state-description messages, we now have a per-object message series for state changes. This makes it possible to pull a fair amount of text out of the arbitrary-messages list and associate those mesages with the objects that conceptually own them.