stfu/Source/oscillators.c

#if defined(STFU_MAIN) && !defined(STFU_OSCILLATORS)
#define STFU_OSCILLATORS

#include <math.h>
#include <stdint.h>

#include "config.h"

/* Intended to be executed offline with values then embedded in the binary.
 * By having usage of glibc sin and cos functions strictly offline it's easier
 * to have it freestanding
 */
struct stfu_sinewave {
  float f, s, c;
} stfu_init_sinewave(float frequency, float phase, float amplitude) {
  struct stfu_sinewave r;
  r.f = 2.f * sinf((float)M_PI * frequency / STFU_AUDIO_FRAME_RATE);
  r.s = amplitude * sinf(phase);
  r.c = amplitude * cosf(phase);
  return r;
}

/* Use `s` for sine value and `c` for cosine on caller side */
struct stfu_sinewave stfu_pump_sinewave(struct stfu_sinewave wave) {
  wave.s -= wave.f * wave.c;
  wave.c += wave.f * wave.s;
  return wave;
}

/* Implemented over sinewave */
struct stfu_sqrtwave {
  struct stfu_sinewave w;
  union {
    float f;
    uint32_t u;
  } v;
} stfu_init_sqrtwave(float frequency, float phase, float amplitude) {
  struct stfu_sqrtwave r;
  union {
    float f;
    uint32_t u;
  } v, a;
  r.w = stfu_init_sinewave(frequency, phase, 1.f);
  v.f = r.w.s;
  a.f = amplitude;
  r.v.u = (a.u & 0x7fffffff) | (v.u & 0x80000000);
  return r;
}

/* Use floating point bit representation to infer sign, all other bits are set
 * to amplitude */
struct stfu_sqrtwave stfu_pump_sqrtwave(struct stfu_sqrtwave wave) {
  union {
    float f;
    uint32_t u;
  } v;
  stfu_pump_sinewave(wave.w);
  v.f = wave.w.s;
  wave.v.u = (wave.v.u & 0x7fffffff) | (v.u & 0x80000000);
  return wave;
}

struct stfu_sawtooth {
  float v, a, i;
} stfu_init_sawtooth(float frequency, float phase, float amplitude) {
  struct stfu_sawtooth r;
  r.v = sinf(phase) * amplitude;
  r.a = amplitude;
  r.i = 2.f * frequency / STFU_AUDIO_FRAME_RATE * amplitude;
  return r;
}

/* Simple amplitude overflow check with truncation */
struct stfu_sawtooth stfu_pump_sawtooth(struct stfu_sawtooth wave) {
  wave.v += wave.i;
  if (wave.v > wave.a)
    wave.v -= wave.a * 2.f;
  return wave;
}

#endif