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ef17694125
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a3f3b3410f
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Title: Programmatic Oscillators
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Brief: Sine, cosine, saw and square oscillators with minimal binary footprint.
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Date: 1684748529
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Tags: Programming, Music, C
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CSS: /style.css
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Wanted to have some beep bops for my [4mb-jam](https://itch.io/jam/4mb-jam-2023) entry, so
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I ended up with implementations of three oscillators that would require minimal amount of calculations.
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Idea is to precalculate initial state offline and only have short frame generation procedure in final binary.
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Thinking about using it in tracker format of sorts that would have runtime generated samples.
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Inspirations are taken from [musicdsp](https://www.musicdsp.org/).
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### Sine/Cosine ###
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```c
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/* Intended to be executed offline with values then embedded in the binary.
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* By having usage of glibc sin and cos functions strictly offline it's easier to have it freestanding
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*/
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struct sinewave {
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float f, s, c;
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} init_sinewave(float frequency, float phase, float amplitude) {
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struct sinewave r;
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r.f = 2.f * sinf((float)M_PI * frequency / AUDIO_FRAME_RATE);
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r.s = amplitude * sinf(phase);
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r.c = amplitude * cosf(phase);
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return r;
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}
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/* Use `s` for sine value and `c` for cosine on caller side */
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void pump_sinewave(struct sinewave *wave) {
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wave->s -= wave->f * wave->c;
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wave->c += wave->f * wave->s;
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}
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```
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### Square ###
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```c
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/* Implemented over sinewave */
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struct sqrtwave {
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struct sinewave w;
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union {
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float f;
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uint32_t u;
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} v;
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} init_sqrtwave(float frequency, float phase, float amplitude) {
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struct sqrtwave r;
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r.w = init_sinewave(frequency, phase, 1.f);
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r.v.f = amplitude;
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return r;
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}
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/* Use floating point bit representation to infer sign, all other bits are set to amplitude */
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void pump_sqrtwave(struct sqrtwave *wave) {
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union {
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float f;
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uint32_t u;
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} v;
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pump_sinewave(&wave->w);
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v.f = wave->w.s;
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wave->v.u = (wave->v.u & 0x7fffffff) | (v.u & 0x80000000);
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}
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```
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### Saw ###
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```c
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struct sawtwave {
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float v, a, i;
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} init_sawtwave(float frequency, float phase, float amplitude) {
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struct sawtwave r;
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r.v = sinf(phase) * amplitude;
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r.a = amplitude;
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r.i = frequency / AUDIO_FRAME_RATE * amplitude;
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return r;
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}
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/* Simple amplitude overflow check with truncation */
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void pump_sawtwave(struct sawtwave *wave) {
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wave->v += wave->i;
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if (wave->v > wave->a)
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wave->v -= wave->a;
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}
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```
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compile.py
Executable file
14
compile.py
Executable file
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#!/usr/bin/python3
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from os import walk
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import subprocess
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subprocess.run("./tools/main_page_generator.py ./articles | ./tools/mmd/build/multimarkdown > ./html/index.html", shell=True)
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subprocess.run("mkdir -p ./html/articles", shell=True)
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for root, dirs, _ in walk("./articles"):
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for d in dirs:
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subprocess.run(
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f"""./tools/article_wrapper.py ./articles/{d}/page.mmd | ./tools/mmd/build/multimarkdown > ./html/articles/{d}.html""",
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shell=True
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)
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compile.sh
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compile.sh
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#!/bin/sh
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mkdir -p ./html/articles
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./tools/main_page_generator.py ./articles | ./tools/mmd/build/multimarkdown > ./html/index.html
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for d in ./articles/*; do
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if [ -d "$d" ]; then
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./tools/article_wrapper.py "$d/page.mmd" | ./tools/mmd/build/multimarkdown > "./html/articles/$(basename -- $d).html"
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fi
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done
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@ -40,6 +40,6 @@ for root, dirs, _ in walk(argv[1]):
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page += f""">*{','.join(metadata["Tags"])}*\n---\n"""
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curtime = time.gmtime(int(time.time()))
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page += f"Last compiled: *{MONTHS[curtime.tm_mon]} {curtime.tm_mday}, {curtime.tm_year} {curtime.tm_hour}:{curtime.tm_min:02d}*\n\n"
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page += f"Last compiled: *{MONTHS[curtime.tm_mon]} {curtime.tm_mday}, {curtime.tm_year} {curtime.tm_hour}:{curtime.tm_min:2}*\n\n"
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print(page_metadata + wrap_page(page))
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