"Woody" OPL3 emulator
=====================

this is the so-called woody opl3 emulator, ripped from DOSBOX svn rev 4391
(November 2020), with full commit history and some tiny touch-ups to make
it compile as C instead of C++.

many adlib/OPL-playing programs use some version of this emulator, but with
C++ and CMake crap added to it, because windows users have been brainwashed
into believing C is inferior to C++, particulary because MSVC++ doesn't even
properly support C. what they don't know is that C compiles a lot faster,
is much simpler and has much more widespread toolchain support.
apart from that it has a stable ABI, and allows to produce much slimmer
executables because libstdc++ (the C++ standard library) doesn't need to
be linked against the executable.

Usage:
======

drop files into your project, include opl.h, and use in your code:

    // initialize the chip(s). samplerate is typicallly 44100.
    adlib_init(samplerate);

    // write a value into a register.
    adlib_write(reg, val);

    // get a sample from the chip.
    int16_t sample;
    adlib_getsample(&sample, 1);

then compile it and link opl.c to your code.
that's pretty much all there is to it.

check https://github.com/digital-sound-antiques/emu2413/blob/master/sample2413.c
for a good example of what and how to feed into the chip, and when to read
samples (and how many) from it.
although the example uses a different chip emulator, the strategy is identical.


License
=======
unfortunately, the code is licensed as LGPL 2.1.

TODO
====
currently the code is not library-safe, as it uses global variables.
optimally all global state is put into a "context" struct and a pointer to
the struct passed to all functions that need access to those variables.
also it would be nice to poke the original authors whether they could relicense
the code as MIT.