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/*
2 
 * Simple mp3 player.  Derived from libmad's example minimad.c.
3 
 */
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#include <u.h>
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#include <libc.h>
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#include "mad.h"
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/* Current input file */
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char *name;
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vlong offset;
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int rate = 44100;
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char *outfile;
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int vfd; /* /dev/volume */
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static enum mad_flow
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input(void *data, struct mad_stream *stream)
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{
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	int fd, n, m;
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	static uchar buf[32768];
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	fd = (int)data;
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	n = stream->bufend - stream->next_frame;
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	memmove(buf, stream->next_frame, n);
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	m = read(fd, buf+n, sizeof buf-n);
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	offset += m;
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	if(m < 0)
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		sysfatal("reading input: %r");
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	if(m == 0)
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		return MAD_FLOW_STOP;
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	n += m;
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	mad_stream_buffer(stream, buf, n);
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	return MAD_FLOW_CONTINUE;
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}
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/*
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 * Dither 28-bit down to 16-bit.  From mpg321.
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 * I'm skeptical, but it's supposed to make the
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 * samples sound better than just truncation.
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 */
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typedef struct Dither Dither;
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struct Dither
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{
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	mad_fixed_t error[3];
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	mad_fixed_t random;
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};
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#define PRNG(x) (((x)*0x19660dL + 0x3c6ef35fL) & 0xffffffffL)
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enum
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{
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	FracBits = MAD_F_FRACBITS,
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	OutBits = 16,
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	Round = 1 << (FracBits+1-OutBits-1),	// sic
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	ScaleBits = FracBits + 1 - OutBits,
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	LowMask  = (1<<ScaleBits) - 1,
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	Min = -MAD_F_ONE,
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	Max = MAD_F_ONE - 1,
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};
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int
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audiodither(mad_fixed_t v, Dither *d)
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{
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	int out;
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	mad_fixed_t random;
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	/* noise shape */
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	v += d->error[0] - d->error[1] + d->error[2];
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	d->error[2] = d->error[1];
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	d->error[1] = d->error[0] / 2;
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	/* bias */
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	out = v + Round;
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	/* dither */
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	random = PRNG(d->random);
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	out += (random & LowMask) - (d->random & LowMask);
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	d->random = random;
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	/* clip */
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	if(out > Max){
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		out = Max;
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		if(v > Max)
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			v = Max;
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	}else if(out < Min){
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		out = Min;
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		if(v < Min)
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			v = Min;
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	}
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	/* quantize */
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	out &= ~LowMask;
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	/* error feedback */
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	d->error[0] = v - out;
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	/* scale */
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	return out >> ScaleBits;
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}
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static enum mad_flow
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output(void *data, struct mad_header const* header, struct mad_pcm *pcm)
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{
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	int i, n, v;
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	mad_fixed_t const *left, *right;
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	static Dither d;
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	static uchar buf[16384], *p;
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	if(pcm->samplerate != rate){
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		rate = pcm->samplerate;
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		if(vfd < 0)
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			fprint(2, "warning: audio sample rate is %d Hz\n", rate);
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		else
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			fprint(vfd, "speed %d", rate);
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	}
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	p = buf;
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	memset(&d, 0, sizeof d);
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	n = pcm->length;
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	switch(pcm->channels){
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	case 1:
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		left = pcm->samples[0];
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		for(i=0; i<n; i++){
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			v = audiodither(*left++, &d);
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			/* stereoize */
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			*p++ = v;
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			*p++ = v>>8;
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			*p++ = v;
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			*p++ = v>>8;
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		}
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		break;
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	case 2:
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		left = pcm->samples[0];
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		right = pcm->samples[1];
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		for(i=0; i<n; i++){
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			v = audiodither(*left++, &d);
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			*p++ = v;
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			*p++ = v>>8;
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			v = audiodither(*right++, &d);
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			*p++ = v;
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			*p++ = v>>8;
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		}
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		break;
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	}
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	assert(p<=buf+sizeof buf);
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	write(1, buf, p-buf);
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	return MAD_FLOW_CONTINUE;
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}
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static enum mad_flow
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error(void *data, struct mad_stream *stream, struct mad_frame *frame)
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{
152 
	if(stream->error == MAD_ERROR_LOSTSYNC)
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		return MAD_FLOW_CONTINUE;
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	sysfatal("%s:#%lld: %s",
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		name, offset-(stream->bufend-stream->next_frame),
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		mad_stream_errorstr(stream));
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	return 0;
158 
}
159 
 
160 
void
161 
play(int fd, char *nam)
162 
{
163 
	struct mad_decoder decoder;
164 
 
165 
	name = nam;
166 
	mad_decoder_init(&decoder, (void*)fd, input, nil, nil, output, error, nil);
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	mad_decoder_run(&decoder, MAD_DECODER_MODE_SYNC);
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	mad_decoder_finish(&decoder);
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}
170 
 
171 
void
172 
usage(void)
173 
{
174 
	fprint(2, "usage: mp3dec [-o outfile] [file...]\n");
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	exits("usage");
176 
}
177 
 
178 
void
179 
main(int argc, char **argv)
180 
{
181 
	int i, fd;
182 
	char *p;
183 
 
184 
	ARGBEGIN{
185 
	case 'o':
186 
		outfile = EARGF(usage());
187 
		break;
188 
	default:
189 
		usage();
190 
	}ARGEND
191 
 
192 
	if(outfile){
193 
		if((fd = create(outfile, OWRITE, 0666)) < 0)
194 
			sysfatal("create %s: %r", outfile);
195 
	}else{
196 
		if((fd = open("/dev/audio", OWRITE)) < 0)
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			sysfatal("open /dev/audio: %r");
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		vfd = open("/dev/volume", OWRITE);
199 
	}
200 
	if(fd != 1){
201 
		dup(fd, 1);
202 
		close(fd);
203 
	}
204 
 
205 
	if(argc == 0){
206 
		play(0, "standard input");
207 
	}else{
208 
		for(i=0; i<argc; i++){
209 
			if((fd = open(argv[i], OREAD)) < 0)
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				sysfatal("open %s: %r", argv[i]);
211 
			play(fd, argv[i]);
212 
			close(fd);
213 
		}
214 
	}
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	exits(0);
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}