Rename hint.txt and hint.text to README.md
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# Most percussive
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Nathan Otterness
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<https://github.com/yalue>
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The code for this entry can be found in prog.c
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## Judges' comments:
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### To use:
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make
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./prog < input.mid > output.mid
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### Try:
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wget -O cvikl.mid 'http://www.kunstderfuge.com/-/midi.asp?file=beethoven/symphony_6_1_(c)cvikl.mid'
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./prog < cvikl.mid > output.mid
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# Play output.mid with your favorite player
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wget -O entertainer.mid https://www.midiworld.com/download/3857
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./prog < entertainer.mid > output2.mid
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# Play output.mid with your favorite player
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### Selected Judges Remarks:
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In an entry that boasts not using literals, one would expect to see straightforward ways to produce
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small integers like `!(x^x)<<!(x^x)`, etc. but this entry is trickier than that. Deciphering what it does,
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apart from reading stdin and writing to stdout, would take a while.
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While doing that, you can be audially *entertained* by a sample of its output.
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## Author's comments:
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### MIDI "boots and cats"
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This program seeks to automatically "improve" standard MIDI files (.mid) by
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adding an extra track that provides a driving drum beat to bring some
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excitement into boring video-game music rips or classical music sequences that
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otherwise only see the light of day when modern musicians import them into FL
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Studio to copy a few chords.
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#### Prerequisites
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If you're not using Windows Media Player or already familiar with MIDI files,
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you may need to install some additional software to be able to listen to them.
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For example, on Ubuntu, I was able to play them in VLC after installing
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`vlc-plugin-fluidsynth` and `fluid-soundfont-gm`.
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You can obtain MIDIs in many places, but I mostly tested the program using
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files I found [here](http://www.kunstderfuge.com/beethoven/variae.htm#Symphonies).
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However, as discussed under the Limitations heading below, not all of them
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work correctly. I will admit to having used
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`http://www.kunstderfuge.com/-/midi.asp?file=beethoven/symphony_6_1_(c)cvikl.mid`
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for most of my testing.
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#### Usage
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Compile the program using the following command (I tested this using both
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`clang` and `gcc`):
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```
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$CC -pedantic -Wall -Werror -Wextra -O3 -o prog prog.c
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```
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The program expects a MIDI on stdin, and writes a modified MIDI to stdout:
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```
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./prog <input.mid >output.mid
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```
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If the program encounters an error, no output will generally be produced, and
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it will exit with a specific status code. Meanings of the various status codes
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are listed below, under the "Program error codes" heading. On success, the
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program exits with a code of 0.
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#### Limitations
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1. The program does not support MIDI files over 4 MB (specifically, it will
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not take input files larger than 2^22 - 1 bytes). This is unlikely to be a
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big limitation in practice, since even lengthy MIDIs are rarely over a
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couple hundred KB.
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2. Not all MIDIs set (or *correctly* set) their timing information, which will
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lead to the tempo of the drum beat not matching the track. This will be
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especially true for "live performance" .mid files.
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3. There may be some types of MIDI messages that the program is unable to
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correctly parse, but I have rarely seen this in practice. The largest
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cause of program failures, in my experience, has been Limitation 2.
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#### Obfuscation notes
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I had one primary goal when writing this program: include no C literals
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whatsoever. The final C file includes no numerical, string, or character
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literals. Instead, all literals have been replaced with a handful of global
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variables, which are occasionally modified throughout the file to prevent
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simple uses of find-and-replace.
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So, in a sense, this obfuscation is simply an intentional use of global
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variables' classic problem: absolute spaghetti code. The absence of any sort
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of literals has the added benefit of forcing any would-be reader to trace the
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contents of many variables starting from `main`, since, without literals, very
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little of the code gives any inherent visual cues as to its purpose.
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I already took the liberty of running `prog.c` through `clang-format`, since it
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still fits in the size limit and the formatting of the code was never intended
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to be an obfuscation technique here.
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#### Other remarks
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MIDI files are generally divided up into one or more "tracks" that play
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concurrently. While it is easy to find the positions of each of these tracks
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in the file, figuring out the amount of time each track is supposed to play is
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more difficult, and requires parsing every track in its entirety. This means
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that generating a drum beat that covers the entire piece of music requires
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parsing every track (the entire file) in order to determine the longest track.
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Once the program has determined the longest track in the file, it generates a
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new track, containing the simple 4-note percussion sequence, to match the
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length (in beats) of the longest-running track. It appends the new track onto
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the end of the file, taking care to update the file header, as well.
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### Program error codes
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If the program encounters an error, it will exit with a nonzero code. The error
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codes can be interpreted as follows:
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- `1`: Encountered an invalid MIDI variable-length integer in the input.
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- `2`: Attempted to write an invalid MIDI variable-length integer to output.
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(This would be an internal error).
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- `3`: Encountered an unsupported MIDI event in the input.
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- `4`: Encountered a bad MIDI track header in the input.
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- `5`: The input MIDI file uses SMPTE time division, which isn't supported.
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- `6`: Failed allocating a temporary buffer to hold a single copy of our "beat"
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messages.
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- `7`: Failed allocating a buffer to hold the new track data.
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- `8`: Failed allocating a buffer to hold the input file.
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- `9`: The input file was too large.
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- `10`: The input file's MIDI header was incorrect (but this isn't checked
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very thoroughly).
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-----------------------------------------------------------------------------------------------------
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(c) Copyright 1984-2020, [Leo Broukhis, Simon Cooper, Landon Curt Noll][judges] - All rights reserved
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This work is licensed under a [Creative Commons Attribution-ShareAlike 3.0 Unported License][cc].
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[judges]: http://www.ioccc.org/judges.html
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[cc]: http://creativecommons.org/licenses/by-sa/3.0/
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-----------------------------------------------------------------------------------------------------
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