Wave generator

wave.c

/*
 * Wave generator
 * by Nathan Korth
 */

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

#define PI 3.14159

#define DEFAULT_LENGTH 1

void writeWAV16(int16_t* samples, uint16_t numChannels, uint32_t numSamples, uint32_t sampleRate, FILE* stream){
    uint32_t formatChunkSize = 16;
    uint32_t dataChunkSize = 4 * numChannels * numSamples;
    uint32_t totalChunkSize = 4 + 8 + formatChunkSize + 8 + dataChunkSize;
    uint16_t waveFormat = 1; // WAVE_FORMAT_PCM
    uint32_t bytesPerSecond = sampleRate * 4 * numChannels;
    uint16_t blockAlign = 4 * numChannels;
    uint16_t bitsPerSample = 8 * 2;

    fputs("RIFF", stream);
    fwrite(&totalChunkSize,     4, 1, stream);
    fputs("WAVE", stream);
    // format chunk
    fputs("fmt ", stream);
    fwrite(&formatChunkSize,    4, 1, stream);
    fwrite(&waveFormat,         2, 1, stream);
    fwrite(&numChannels,        2, 1, stream);
    fwrite(&sampleRate,         4, 1, stream);
    fwrite(&bytesPerSecond,     4, 1, stream);
    fwrite(&blockAlign,         2, 1, stream);
    fwrite(&bitsPerSample,      2, 1, stream);
    // data chunk
    fputs("data", stream);
    fwrite(&dataChunkSize,      4, 1, stream);
    fwrite(samples, sizeof(int16_t), numSamples, stream);
}

void usage(char* invocation){
    fprintf(stderr,
            "Usage: %s -f FREQUENCY [options] > filename.wav\n"
            "Options:\n"
            "  -f FREQUENCY, --frequency=FREQUENCY  Set frequency in Hz.\n"
            "  -h, --help                           Print this message and exit.\n"
            "  -l SECONDS, --length=SECONDS         Set length in seconds. (default %d)\n"
            "  -w NAME, --waveform=NAME             Set waveform to sine, saw, or square.\n",
            invocation, DEFAULT_LENGTH);
}

double waveform_sine(double t){
    return sin(2 * PI * t);
}

double waveform_saw(double t){
    double intpart; // discarded
    return -1 + 2 * modf(t, &intpart);
}

double waveform_square(double t){
    double intpart;
    return modf(t, &intpart) > 0.5 ? -1 : 1;
}

int main(int argc, char* argv[]){
    int frequency = 0;
    int length = DEFAULT_LENGTH;
    double (*waveform)(double) = waveform_sine;

    static struct option longopts[] = {
        {"frequency",   required_argument,  NULL,   'f'},
        {"help",        no_argument,        NULL,   'h'},
        {"length",      required_argument,  NULL,   'l'},
        {"waveform",    required_argument,  NULL,   'w'}
    };
    char flag;
    while((flag = getopt_long(argc, argv, "f:hl:w:", longopts, NULL)) != -1){
        switch(flag){
            case 'f':
                frequency = atoi(optarg);
                break;
            case 'h':
                usage(argv[0]);
                return 0;
            case 'l':
                length = atoi(optarg);
                break;
            case 'w':
                if(strcmp(optarg, "sine") == 0){
                    waveform = waveform_sine;
                } else if(strcmp(optarg, "saw") == 0){
                    waveform = waveform_saw;
                } else if(strcmp(optarg, "square") == 0){
                    waveform = waveform_square;
                } else{
                    fputs("Unrecognized waveform.\n", stderr);
                    return 1;
                }
                break;
        }
    }
    if(frequency == 0 || length == 0){
        usage(argv[0]);
        return 1;
    }

    int sampleRate = 44100;
    uint32_t numSamples = sampleRate * length;

    int16_t samples[numSamples];
    for(uint32_t i = 0; i < numSamples; ++i){
        double t = ((double) i) / sampleRate * frequency;
        double sample_float = waveform(t);
        samples[i] = sample_float * INT16_MAX;
    }

    writeWAV16(samples, 1, numSamples, sampleRate, stdout);

    return 0;
}