making audio from recursive sequences

recursive_sequences_audio.c

#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <assert.h>
#include <string.h>
#include <math.h>

void putu32(FILE* f, uint32_t x) {
	for(int i = 0; i < 4; ++i) {
		putc(x&0xFF, f);
		x = x>>8;
	}
}

void putu16(FILE* f, uint16_t x) {
	for(int i = 0; i < 2; ++i) {
		putc(x&0xFF, f);
		x = x>>8;
	}
}

int main(int argc, char** argv) {
	FILE* f = stdout;
	assert(f);

	static const int sample_count = 4000;
	static const uint32_t sample_rate = 4410;
	static const float gain = 30.0;

	int r[sample_count];
	for(int i = 0; i < sample_count; ++i) r[i] = 1;

	switch(argv[1][0]) {
	case 'c':
		for(int i = 3; i < sample_count; ++i) r[i] = r[i-r[i-1]] + r[i-r[i-2]];
		for(int i = 0; i < sample_count; ++i) r[i] -= i/2;
		break;
	case 'e':
		for(int i = 3; i < sample_count; ++i) r[i] = r[r[i-1]] + r[i-r[i-2]-1];
		for(int i = 0; i < sample_count; ++i) r[i] -= i/2;
		break;
	case 'f':
		for(int i = 3; i < sample_count; ++i) r[i] = r[r[i-1]] + r[i-2*r[i-2]+1];
		for(int i = 0; i < sample_count; ++i) r[i] -= (int)(0.42*pow(i, 0.878));
		break;
	}

	//set up sample rate and such
	static const uint16_t channels = 1;
	static const uint32_t bytes_per_sample = 2;
	uint32_t data_size = sample_count *bytes_per_sample * channels;

	//RIFF chunk
	fprintf(f, "RIFF");
	putu32(f, data_size + 36);
	fprintf(f, "WAVE");

	//fmt chunk
	fprintf(f, "fmt ");
	putu32(f, 16); //size of this chunk
	putu16(f, 1); //1 = PCM
	putu16(f, channels);
	putu32(f, sample_rate);
	putu32(f, sample_rate * bytes_per_sample * channels);
	putu16(f, bytes_per_sample * channels);
	putu16(f, bytes_per_sample * 8);

	//data chunk
	fprintf(f, "data");
	putu32(f, data_size);

	for(int sample = 0; sample < sample_count; ++sample) {
		int x = r[sample] * gain;
		uint16_t pcm_sample = (int16_t)(x);
		putu16(f, pcm_sample);
	}
}