= Open Adventure Maintainer's Notes =
by Eric S. Raymond

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 link:history.html[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 Nilson in restructuring some particularly grotty gotos is
gratefully acknowledged.

== 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.  By policy, all
user-visible changes must be revertible with the -o (oldstyle) option.

It is a goal of this project to exactly preserve the *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 ==

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) version reverts the 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, it
is compiled at build time to a source module containing C structures,
which is then linked to the advent binary.

The game-save format has changed.  This was done to simplify
FORTRAN-derived code that formerly implemented these 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.

== 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 comprehesive test suite that we built first and verified with
coverage tools. This is what you are running when you do "make check".

This move 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 are still in the process of removing 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... 

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 of these
  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.

* The code still has an unfortunately high density of magic numbers - in
  particular, numeric object and room IDs.  There are plans to fix this.

* Much of the code still uses FORTRAN-style uppercase names.

* 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.

// end
