/* a440.c   by Michael Thorpe   2009-07-13 */

#include <math.h>
#include <stdio.h>
#include <stdlib.h>

#define SAMPLES_PER_SECOND 44100
#define SAMPLES_PER_BLOCK (SAMPLES_PER_SECOND/100)
#define MAX_VOLUME 32767

struct note {
	double freq;
	double phase;
};

const char usage[]="usage: a440 <note1 (0==a440)> [<note2> [..]]\n";

int main(int argc,char **argv) {
	const double samplelength=1.0/(double)SAMPLES_PER_SECOND;
	const double freqmultiplier=samplelength*2*M_PI;
	signed short samples[SAMPLES_PER_BLOCK];
	int i,j,numnotes;
	long l;
	struct note *notes;
	long transpose=0;
	char *tmp;

	tmp=getenv("A440_TRANSPOSE");
	if(tmp) {
		transpose=strtol(tmp,&tmp,10);
		if(*tmp) {
			fputs("A440_TRANSPOSE must be a valid integer\n",stderr);
			transpose=0;
		}
	}
	if(argc<=1) {
		fputs(usage,stderr);
		return(1);
	}
	numnotes=argc-1;
	notes=(struct note *)calloc(numnotes,sizeof(struct note));
	if(!notes) {
		perror("calloc");
		return(1);
	}
	for(j=0;j<numnotes;j++) {
		l=strtol(argv[j+1],&tmp,10);
		if(*tmp) {
			fputs(usage,stderr);
			return(1);
		}
		notes[j].freq=440.0*pow(2.0,((double)(l+transpose))/12.0);
		notes[j].phase=0;
	}
	while(1) {
		for(i=0;i<SAMPLES_PER_BLOCK;i++) {
			samples[i]=0;
			for(j=0;j<numnotes;j++) {
				notes[j].phase+=freqmultiplier*notes[j].freq;
				if(2*M_PI<notes[j].phase)
					notes[j].phase-=2*M_PI;
				samples[i]+=MAX_VOLUME*sin(notes[j].phase)/numnotes;
			}
		}
		fwrite(samples,sizeof(signed short),SAMPLES_PER_BLOCK,stdout);
	}
}