path: root/engines/sci/sfx/mixer/soft.cpp

/***************************************************************************
 mixer.c Copyright (C) 2003 Christoph Reichenbach


 This program may be modified and copied freely according to the terms of
 the GNU general public license (GPL), as long as the above copyright
 notice and the licensing information contained herein are preserved.

 Please refer to www.gnu.org for licensing details.

 This work is provided AS IS, without warranty of any kind, expressed or
 implied, including but not limited to the warranties of merchantibility,
 noninfringement, and fitness for a specific purpose. The author will not
 be held liable for any damage caused by this work or derivatives of it.

 By using this source code, you agree to the licensing terms as stated
 above.


 Please contact the maintainer for bug reports or inquiries.

 Current Maintainer:

    Christoph Reichenbach (CR) <jameson@linuxgames.com>

***************************************************************************/

#include "../mixer.h"
#include "sci/include/sci_memory.h"

/* Max. number of microseconds in difference allowed between independent audio streams */
#define TIMESTAMP_MAX_ALLOWED_DELTA 2000

/*#define DEBUG 3*/
/* Set DEBUG to one of the following:
** anything -- high-level debugging (feed subscriptions/deletions etc.)
**     >= 1 -- rough input and output analysis (once per call)
**     >= 2 -- more detailed input analysis (once per call and feed)
**     >= 3 -- fully detailed input and output analysis (once per frame and feed)
*/

/*#define DEBUG 0*/

#define MIN_DELTA_OBSERVATIONS 100 /* Number of times the mixer is called before it starts trying to improve latency */
#define MAX_DELTA_OBSERVATIONS 1000000 /* Number of times the mixer is called before we assume we truly understand timing */

static int diagnosed_too_slow = 0;

static volatile int mixer_lock = 0;

/*#define DEBUG_LOCKS*/
#ifdef DEBUG_LOCKS
#  define DEBUG_ACQUIRE fprintf(stderr, "[ -LOCK -] ACKQ %d: %d\n", __LINE__, mixer_lock)
#  define DEBUG_WAIT fprintf(stderr, "[ -LOCK -] WAIT %d: %d\n", __LINE__, mixer_lock);
#  define DEBUG_RELEASE ; fprintf(stderr, "[ -LOCK -] REL %d: %d\n", __LINE__, mixer_lock);
#else
#  define DEBUG_ACQUIRE
#  define DEBUG_WAIT
#  define DEBUG_RELEASE
#endif

#define ACQUIRE_LOCK() ++mixer_lock; while (mixer_lock != 1) { DEBUG_WAIT sci_sched_yield(); } DEBUG_ACQUIRE
#define RELEASE_LOCK() --mixer_lock DEBUG_RELEASE

struct mixer_private {
	byte *outbuf; /* Output buffer to write to the PCM device next time */
	sfx_timestamp_t outbuf_timestamp; /* Timestamp associated with the output buffer */
	int have_outbuf_timestamp; /* Whether we really _have_ an associated timestamp */
	byte *writebuf; /* Buffer we're supposed to write to */
	gint32 *compbuf_l, *compbuf_r; /* Intermediate buffers for computation */
	int lastbuf_len; /* Number of frames stored in the last buffer */

	long skew; /* Millisecond relative to which we compute time. This is the millisecond
		   ** part of the first time we emitted sound, to simplify some computations.  */
	long lsec; /* Last point in time we updated buffers, if any (seconds since the epoch) */
	int played_this_second; /* Number of frames emitted so far in second lsec */

	int max_delta; /* maximum observed time delta (using 'frames' as a metric unit) */
	int delta_observations; /* Number of times we played; confidence measure for max_delta */

	/* Pause data */
	int paused;
};

#define P ((struct mixer_private *)(self->private_bits))


static int
mix_init(sfx_pcm_mixer_t *self, sfx_pcm_device_t *device)
{
	self->dev = device;
	self->private_bits /* = P */ = sci_malloc(sizeof(struct mixer_private));
	P->outbuf = P->writebuf = NULL;
	P->lastbuf_len = 0;
	P->compbuf_l = (gint32*)sci_malloc(sizeof(gint32) * device->buf_size);
	P->compbuf_r = (gint32*)sci_malloc(sizeof(gint32) * device->buf_size);
	P->played_this_second = 0;
	P->paused = 0;
#ifdef DEBUG
	sciprintf("[soft-mixer] Initialised device %s v%s (%d Hz, %d/%x)\n",
		  device->name, device->version,
		  device->conf.rate, device->conf.stereo, device->conf.format);
#endif
	return SFX_OK;
}

static inline unsigned int
gcd(unsigned int a, unsigned int b)
{
	if (a == b)
		return a;

	if (a < b) {
		unsigned int c = b % a;

		if (!c)
			return a;

		return gcd(c, a);
	} else
		return gcd(b, a);
}

static sfx_pcm_urat_t
urat(unsigned int nom, unsigned int denom)
{
	sfx_pcm_urat_t rv;
	unsigned int g;

	rv.val = nom / denom;
	nom -= rv.val * denom;
	if (nom == 0)
		g = 1;
	else
		g = gcd(nom, denom);

	rv.nom = nom / g;
	rv.den = denom / g;

	return rv;
}

static void
mix_subscribe(sfx_pcm_mixer_t *self, sfx_pcm_feed_t *feed)
{
	sfx_pcm_feed_state_t *fs;
	ACQUIRE_LOCK();
	if (!self->feeds) {
		self->feeds_allocd = 2;
		self->feeds = (sfx_pcm_feed_state_t*)sci_malloc(sizeof(sfx_pcm_feed_state_t)
					 * self->feeds_allocd);
	} else if (self->feeds_allocd == self->feeds_nr) {
		self->feeds_allocd += 2;
		self->feeds = (sfx_pcm_feed_state_t*)sci_realloc(self->feeds,
					  sizeof(sfx_pcm_feed_state_t)
					  * self->feeds_allocd);
	}

	fs = self->feeds + self->feeds_nr++;
	fs->feed = feed;

	feed->frame_size = SFX_PCM_FRAME_SIZE(feed->conf);

	/*	fs->buf_size = (self->dev->buf_size
			  * (feed->conf.rate
			     + self->dev->conf.rate - 1))
		/ self->dev->conf.rate;
	*/
	/* For the sake of people without 64 bit CPUs: */
	fs->buf_size = 2 + /* Additional safety */
		(self->dev->buf_size *
			(1 + (feed->conf.rate / self->dev->conf.rate)));
fprintf(stderr, " ---> %d/%d/%d/%d = %d\n",
	self->dev->buf_size,
	feed->conf.rate,
	self->dev->conf.rate,
	feed->frame_size,
	fs->buf_size);

	fs->buf = (byte*)sci_malloc(fs->buf_size * feed->frame_size);
fprintf(stderr, " ---> --> %d for %p at %p\n", fs->buf_size * feed->frame_size, (void *)fs, (void *)fs->buf);
{int i; for (i = 0; i < fs->buf_size * feed->frame_size; i++)
fs->buf[i] = 0xa5; }
	fs->scount = urat(0, 1);
	fs->spd = urat(feed->conf.rate, self->dev->conf.rate);
	fs->scount.den = fs->spd.den;
	fs->ch_old.left = 0;
	fs->ch_old.right = 0;
	fs->ch_new.left = 0;
	fs->ch_new.right = 0;
	fs->mode = SFX_PCM_FEED_MODE_ALIVE;

	/* If the feed can't provide us with timestamps, we don't need to wait for it to do so */
	fs->pending_review = (feed->get_timestamp)? 1 : 0;

	fs->frame_bufstart = 0;

#ifdef DEBUG
	sciprintf("[soft-mixer] Subscribed %s-%x (%d Hz, %d/%x) at %d+%d/%d, buffer size %d\n",
		  feed->debug_name, feed->debug_nr, feed->conf.rate, feed->conf.stereo, feed->conf.format,
		  fs->spd.val, fs->spd.nom, fs->spd.den, fs->buf_size);
#endif
	RELEASE_LOCK();
}


static void
_mix_unsubscribe(sfx_pcm_mixer_t *self, sfx_pcm_feed_t *feed)
{
	int i;
#ifdef DEBUG
	sciprintf("[soft-mixer] Unsubscribing %s-%x\n", feed->debug_name, feed->debug_nr);
#endif
	for (i = 0; i < self->feeds_nr; i++) {
		sfx_pcm_feed_state_t *fs = self->feeds + i;

		if (fs->feed == feed) {
			feed->destroy(feed);

			if (fs->buf)
				sci_free(fs->buf);

			self->feeds_nr--;

			/* Copy topmost into deleted so that we don't have any holes */
			if (i != self->feeds_nr)
				self->feeds[i] = self->feeds[self->feeds_nr];

			if (self->feeds_allocd > 8 && self->feeds_allocd > (self->feeds_nr << 1)) {
				/* Limit memory waste */
				self->feeds_allocd >>= 1;
				self->feeds
					= (sfx_pcm_feed_state_t*)sci_realloc(self->feeds,
						      sizeof(sfx_pcm_feed_state_t)
						      * self->feeds_allocd);
			}

			for (i = 0; i < self->feeds_nr; i++)
				fprintf(stderr, "  Feed #%d: %s-%x\n",
					i, self->feeds[i].feed->debug_name,
					self->feeds[i].feed->debug_nr);

			return;
		}
	}

	fprintf(stderr, "[sfx-mixer] Assertion failed: Deleting invalid feed %p out of %d\n", 
		(void *)feed, self->feeds_nr);

	BREAKPOINT();
}

static void
mix_exit(sfx_pcm_mixer_t *self)
{
	ACQUIRE_LOCK();
	while (self->feeds_nr)
		_mix_unsubscribe(self, self->feeds[0].feed);

	if (P->outbuf)
		sci_free(P->outbuf);
	if (P->writebuf)
		sci_free(P->writebuf);

	if (P->compbuf_l)
		sci_free(P->compbuf_l);
	if (P->compbuf_l)
		sci_free(P->compbuf_r);

	sci_free(P);
	self->private_bits /* = P */ = NULL;
	RELEASE_LOCK();

#ifdef DEBUG
	sciprintf("[soft-mixer] Uninitialising mixer\n");
#endif
}


#define LIMIT_16_BITS(v)			\
		if (v < -32767)			\
			v = -32768;		\
		else if (v > 32766)		\
			v = 32767

static inline void
mix_compute_output(sfx_pcm_mixer_t *self, int outplen)
{
	int frame_i;
	sfx_pcm_config_t conf = self->dev->conf;
	int use_16 = conf.format & SFX_PCM_FORMAT_16;
	int bias = conf.format & ~SFX_PCM_FORMAT_LMASK;
	byte *lchan, *rchan = NULL;
	/* Don't see how this could possibly wind up being
	** used w/o initialisation, but you never know... */
	gint32 *lsrc = P->compbuf_l;
	gint32 *rsrc = P->compbuf_r;
	int frame_size = SFX_PCM_FRAME_SIZE(conf);


	if (!P->writebuf)
		P->writebuf = (byte*)sci_malloc(self->dev->buf_size * frame_size + 4);

	if (conf.stereo) {
		if (conf.stereo == SFX_PCM_STEREO_RL) {
			lchan = P->writebuf + ((use_16)? 2 : 1);
			rchan = P->writebuf;
		} else {
			lchan = P->writebuf;
			rchan = P->writebuf + ((use_16)? 2 : 1);
		}
	} else
		lchan = P->writebuf;


	for (frame_i = 0; frame_i < outplen; frame_i++) {
		int left = *lsrc++;
		int right = *rsrc++;

		if (conf.stereo) {
			LIMIT_16_BITS(left);
			LIMIT_16_BITS(right);

			if (!use_16) {
				left >>= 8;
				right >>= 8;
			}

			left += bias;
			right += bias;

			if (use_16) {
				if (SFX_PCM_FORMAT_LE == (conf.format & SFX_PCM_FORMAT_ENDIANNESS)) {
					lchan[0] = left & 0xff;
					lchan[1] = (left >> 8) & 0xff;
					rchan[0] = right & 0xff;
					rchan[1] = (right >> 8) & 0xff;
				} else {
					lchan[1] = left & 0xff;
					lchan[0] = (left >> 8) & 0xff;
					rchan[1] = right & 0xff;
					rchan[0] = (right >> 8) & 0xff;
				}

				lchan += 4;
				rchan += 4;
			} else {
				*lchan = left & 0xff;
				*rchan = right & 0xff;

				lchan += 2;
				rchan += 2;
			}

		} else {
			left += right;
			left >>= 1;
			LIMIT_16_BITS(left);
			if (!use_16)
				left >>= 8;

			left += bias;

			if (use_16) {
				if (SFX_PCM_FORMAT_LE == (conf.format & SFX_PCM_FORMAT_ENDIANNESS)) {
					lchan[0] = left & 0xff;
					lchan[1] = (left >> 8) & 0xff;
				} else {
					lchan[1] = left & 0xff;
					lchan[0] = (left >> 8) & 0xff;
				}

				lchan += 2;
			} else {
				*lchan = left & 0xff;
				lchan += 1;
			}
		}
	}
}

static inline void
mix_swap_buffers(sfx_pcm_mixer_t *self)
{ /* Swap buffers */
	byte *tmp = P->outbuf;
	P->outbuf = P->writebuf;
	P->writebuf = tmp;
}


#define FRAME_OFFSET(usecs) \
			((usecs >> 7) /* approximate, since uint32 is too small */ \
			 * ((long) self->dev->conf.rate)) \
			/ (1000000L >> 7)

static inline int
mix_compute_buf_len(sfx_pcm_mixer_t *self, int *skip_frames)
     /* Computes the number of frames we ought to write. It tries to minimise the number,
     ** in order to reduce latency. */
     /* It sets 'skip_frames' to the number of frames to assume lost by latency, effectively
     ** skipping them.  */
{
	int free_frames;
	int played_frames = 0; /* since the last call */
	long secs, usecs;
	int frame_pos;
	int result_frames;

	sci_gettime(&secs, &usecs);

	if (!P->outbuf) {
		/* Called for the first time ever? */
		P->skew = usecs;
		P->lsec = secs;
		P->max_delta = 0;
		P->delta_observations = 0;
		P->played_this_second = 0;
		*skip_frames = 0;
		return self->dev->buf_size;
	}

	/*	fprintf(stderr, "[%d:%d]S%d ", secs, usecs, P->skew);*/

	if (P->skew > usecs) {
		secs--;
		usecs += (1000000 - P->skew);
	}
	else
		usecs -= P->skew;

	frame_pos = FRAME_OFFSET(usecs);

	played_frames = frame_pos - P->played_this_second
		+ ((secs - P->lsec) * self->dev->conf.rate);
	/*
	fprintf(stderr, "%d:%d - %d:%d  => %d\n", secs, frame_pos,
		P->lsec, P->played_this_second, played_frames);
	*/

	if (played_frames > self->dev->buf_size)
		played_frames = self->dev->buf_size;

	/*
	fprintf(stderr, "Between %d:? offset=%d and %d:%d offset=%d: Played %d at %d\n", P->lsec, P->played_this_second,
	secs, usecs, frame_pos, played_frames, self->dev->conf.rate);
	*/


	if (played_frames > P->max_delta)
		P->max_delta = played_frames;

	free_frames = played_frames;

	if (free_frames > self->dev->buf_size) {
		if (!diagnosed_too_slow) {
			sciprintf("[sfx-mixer] Your timer is too slow for your PCM output device (%d/%d), free=%d.\n"
				  "[sfx-mixer] You might want to try changing the device, timer, or mixer, if possible.\n",
				  played_frames, self->dev->buf_size, free_frames);
		}
		diagnosed_too_slow = 1;

		*skip_frames = free_frames - self->dev->buf_size;
		free_frames = self->dev->buf_size;
	} else
		*skip_frames = 0;

	++P->delta_observations;
	if (P->delta_observations > MAX_DELTA_OBSERVATIONS)
		P->delta_observations = MAX_DELTA_OBSERVATIONS;

/* 	/\* Disabled, broken *\/ */
/* 	if (0 && P->delta_observations > MIN_DELTA_OBSERVATIONS) { /\* Start improving after a while *\/ */
/* 		int diff = self->dev->conf.rate - P->max_delta; */

/* 		/\* log-approximate P->max_delta over time *\/ */
/* 		recommended_frames = P->max_delta + */
/* 			((diff * MIN_DELTA_OBSERVATIONS) / P->delta_observations); */
/* /\* WTF? *\/ */
/* 	} else */
/* 		recommended_frames = self->dev->buf_size; /\* Initially, keep the buffer full *\/ */

#if (DEBUG >= 1)
	sciprintf("[soft-mixer] played since last time: %d, recommended: %d, free: %d\n",
		  played_frames, recommended_frames, free_frames);
#endif

	result_frames = free_frames;

	if (result_frames < 0)
		result_frames = 0;

	P->played_this_second += result_frames;
	while (P->played_this_second >= self->dev->conf.rate) {
		/* Won't normally happen more than once */
		P->played_this_second -= self->dev->conf.rate;
		P->lsec++;
	}

	if (result_frames > self->dev->buf_size) {
		fprintf(stderr, "[soft-mixer] Internal assertion failed: frames-to-write %d > %d\n",
			result_frames, self->dev->buf_size);
	}
	return result_frames;
}



#define READ_NEW_VALUES() \
		if (frames_left > 0) {						\
			if (bias) { /* unsigned data */					\
				if (!use_16) {						\
					c_new.left = (*lsrc) << 8;			\
					c_new.right = (*rsrc) << 8;			\
				} else {						\
					if (conf.format & SFX_PCM_FORMAT_LE) {		\
						c_new.left = lsrc[0] | lsrc[1] << 8;	\
						c_new.right = rsrc[0] | rsrc[1] << 8;	\
					} else {					\
						c_new.left = lsrc[1] | lsrc[0] << 8;	\
						c_new.right = rsrc[1] | rsrc[0] << 8;	\
					}						\
				}							\
			} else { /* signed data */							\
				if (!use_16) {								\
					c_new.left = (*((signed char *)lsrc)) << 8;			\
					c_new.right = (*((signed char *)rsrc)) << 8;			\
				} else {								\
					if (conf.format & SFX_PCM_FORMAT_LE) {				\
						c_new.left = lsrc[0] | ((signed char *)lsrc)[1] << 8;	\
						c_new.right = rsrc[0] | ((signed char *)rsrc)[1] << 8;	\
					} else {							\
						c_new.left = lsrc[1] | ((signed char *)lsrc)[0] << 8;	\
						c_new.right = rsrc[1] | ((signed char *)rsrc)[0] << 8;	\
					}								\
				}									\
			}										\
										\
			c_new.left -= bias;					\
			c_new.right -= bias;					\
										\
			lsrc += frame_size;					\
			rsrc += frame_size;					\
		} else {							\
			c_new.left = c_new.right = 0;				\
			break;							\
		}


static volatile int xx_offset;
static volatile int xx_size;

static void
mix_compute_input_linear(sfx_pcm_mixer_t *self, int add_result,
			 int len, sfx_timestamp_t *ts, sfx_timestamp_t base_ts)
     /* if add_result is non-zero, P->outbuf should be added to rather than overwritten. */
     /* base_ts is the timestamp for the first frame */
{
	sfx_pcm_feed_state_t *fs = self->feeds + add_result;
	sfx_pcm_feed_t *f = fs->feed;
	sfx_pcm_config_t conf = f->conf;
	int use_16 = conf.format & SFX_PCM_FORMAT_16;
	gint32 *lchan = P->compbuf_l;
	gint32 *rchan = P->compbuf_r;
	int frame_size = f->frame_size;
	byte *wr_dest = fs->buf + (frame_size * fs->frame_bufstart);
	byte *lsrc = fs->buf;
	byte *rsrc = fs->buf;
	/* Location to write to */
	int frames_nr;
	int bias = (conf.format & ~SFX_PCM_FORMAT_LMASK)? 0x8000 : 0;
	/* We use this only on a 16 bit level here */

	/* The two most extreme source frames we consider for a
	** destination frame  */
	struct twochannel_data c_old = fs->ch_old;
	struct twochannel_data c_new = fs->ch_new;

	int frames_read = 0;
	int frames_left;
	int write_offset; /* Iterator for translation */
	int delay_frames = 0; /* Number of frames (dest buffer) at the beginning we skip */

	/* First, compute the number of frames we want to retreive */
	frames_nr = fs->spd.val * len;
	/* A little complicated since we must consider partial frames */
	frames_nr += (fs->spd.nom * len
		       + (fs->scount.den - fs->scount.nom) /* remember that we may have leftovers */
		       + (fs->spd.den - 1 /* round up */)
		       )
		/ fs->spd.den;

	ts->secs = -1;

	if (frames_nr > fs->buf_size) {
		fprintf(stderr, "%d (%d*%d + somethign) bytes, but only %d allowed!!!!!\n",
			frames_nr * f->frame_size,
			fs->spd.val, len,
			fs->buf_size);
		BREAKPOINT();
	}

	if (fs->pending_review) {
		int newmode = PCM_FEED_EMPTY; /* empty unless a get_timestamp() tells otherwise */

		RELEASE_LOCK();
		/* Retrieve timestamp */
		if (f->get_timestamp)
			newmode = f->get_timestamp(f, ts);
		ACQUIRE_LOCK();

		fs = self->feeds + add_result;
		/* Reset in case of status update */

		switch (newmode) {

		case PCM_FEED_TIMESTAMP: {
			/* Compute the number of frames the returned timestamp is in the future: */
			delay_frames =
				sfx_timestamp_frame_diff(sfx_timestamp_renormalise(*ts, base_ts.frame_rate),
							  base_ts);

			if (delay_frames <= 0)
				/* Start ASAP, even if it's too late */
				delay_frames = 0;
			else
				if (delay_frames > len)
					delay_frames = len;
			fs->pending_review = 0;
		}
			break;

		case PCM_FEED_EMPTY:
			fs->mode = SFX_PCM_FEED_MODE_DEAD;

			/* ...fall through... */

		case PCM_FEED_IDLE:
			/* Clear audio buffer, if neccessary, and return */
			if (!add_result) {
				memset(P->compbuf_l, 0, sizeof(gint32) * len);
				memset(P->compbuf_r, 0, sizeof(gint32) * len);
			}
			return;

		default:
			fprintf(stderr, "[soft-mixer] Fatal: Invalid mode returned by PCM feed %s-%d's get_timestamp(): %d\n",
				f->debug_name, f->debug_nr, newmode);
			exit(1);
		}
	}

	RELEASE_LOCK();
	/* Make sure we have sufficient information */
	if (frames_nr > delay_frames + fs->frame_bufstart)
		frames_read =
			f->poll(f, wr_dest,
				frames_nr
				- delay_frames
				- fs->frame_bufstart);

	ACQUIRE_LOCK();
	fs = self->feeds + add_result;

	frames_read += fs->frame_bufstart;
	frames_left = frames_read;

	/* Reset in case of status update */

	/* Skip at the beginning: */
	if (delay_frames) {
		if (!add_result) {
			memset(lchan, 0, sizeof(gint32) * delay_frames);
			memset(rchan, 0, sizeof(gint32) * delay_frames);
		}
		lchan += delay_frames;
		rchan += delay_frames;

		len -= delay_frames;
	}


#if (DEBUG >= 2)
	sciprintf("[soft-mixer] Examining %s-%x (frame size %d); read %d/%d/%d, re-using %d frames\n",
		  f->debug_name, f->debug_nr, frame_size, frames_read, frames_nr,
		  fs->buf_size, fs->frame_bufstart);
#endif


	if (conf.stereo == SFX_PCM_STEREO_LR)
		rsrc += (use_16)? 2 : 1;
	else if (conf.stereo == SFX_PCM_STEREO_RL)
		lsrc += (use_16)? 2 : 1;
	/* Otherwise, we let both point to the same place */

#if (DEBUG >= 2)
	sciprintf("[soft-mixer] Stretching theoretical %d (physical %d) results to %d\n", frames_nr, frames_left, len);
#endif
	for (write_offset = 0; write_offset < len; write_offset++) {
		int leftsum = 0; /* Sum of any complete frames we used */
		int rightsum = 0;

		int left; /* Sum of the two most extreme source frames
			  ** we considered, i.e. the oldest and newest
			  ** one corresponding to the output frame we are
			  ** computing  */
		int right;

		int frame_steps = fs->spd.val;
		int j;

		if (fs->scount.nom >= fs->scount.den) {
			fs->scount.nom -= fs->scount.den; /* Ensure fractional part < 1 */
			++frame_steps;
		}
		if (frame_steps)
			c_old = c_new;

#if 0
		if (write_offset == 0) {
			READ_NEW_VALUES();
			--frames_left;
#if (DEBUG >= 3)
			sciprintf("[soft-mixer] Initial read %d:%d\n", c_new.left, c_new.right);
#endif
			c_old = c_new;
			}
#endif

		for (j = 0; j < frame_steps; j++) {
			READ_NEW_VALUES();
			--frames_left;
#if (DEBUG >= 3)
			sciprintf("[soft-mixer] Step %d/%d made %d:%d\n", j, frame_steps, c_new.left, c_new.right);
#endif

			/* The last frame will be subject to the fractional
			** part analysis, so we add it to 'left' and 'right'
			** later-- all others are added to (leftsum, rightsum).
			*/
			if (j+1 < frame_steps) {
				leftsum += c_new.left;
				rightsum += c_new.right;
			}
		}

		left = c_new.left * fs->scount.nom
			+ c_old.left * (fs->scount.den - fs->scount.nom);
		right = c_new.right * fs->scount.nom
			+ c_old.right * (fs->scount.den - fs->scount.nom);

		/* Normalise */
		left  /= fs->spd.den;
		right /= fs->spd.den;


		leftsum += left;
		rightsum += right;


		/* Make sure to divide by the number of frames we added here */
		if (frame_steps > 1) {
			leftsum  /= (frame_steps);
			rightsum /= (frame_steps);
		}


#if (DEBUG >= 3)
		sciprintf("[soft-mixer] Ultimate result: %d:%d (frac %d:%d)\n", leftsum, rightsum, left, right);
#endif

		if (add_result) {
			*(lchan++) += leftsum;
			*(rchan++) += rightsum;
		} else {
			*(lchan++) = leftsum;
			*(rchan++) = rightsum;
		}

		fs->scount.nom += fs->spd.nom; /* Count up fractional part */
	}

	fs->ch_old = c_old;
	fs->ch_new = c_new;

	/* If neccessary, zero out the rest */
	if (write_offset < len && !add_result) {
		memset(lchan, 0, sizeof(gint32) * (len - write_offset));
		memset(rchan, 0, sizeof(gint32) * (len - write_offset));
	}

	/* Save whether we have a partial frame still stored */
	fs->frame_bufstart = frames_left;

	if (frames_left) {
		xx_offset = ((frames_read - frames_left) * f->frame_size);
		xx_size = frames_left * f->frame_size;
		if (xx_offset + xx_size
		    >= fs->buf_size * f->frame_size) {
			fprintf(stderr, "offset %d >= max %d!\n",
				(xx_offset + xx_size), fs->buf_size * f->frame_size);
			BREAKPOINT();
		}

		memmove(fs->buf,
			fs->buf + ((frames_read - frames_left) * f->frame_size),
			frames_left * f->frame_size);
	}
#if (DEBUG >= 2)
	sciprintf("[soft-mixer] Leaving %d over\n", fs->frame_bufstart);
#endif

	if (frames_read + delay_frames < frames_nr) {
		if (f->get_timestamp) /* Can resume? */
			fs->pending_review = 1;
		else
			fs->mode = SFX_PCM_FEED_MODE_DEAD; /* Done. */
	}
}

static int
mix_process_linear(sfx_pcm_mixer_t *self)
{
ACQUIRE_LOCK();
{
	int src_i; /* source feed index counter */
	int frames_skip; /* Number of frames to discard, rather than to emit */
	int buflen = mix_compute_buf_len(self, &frames_skip); /* Compute # of frames we must compute and write */
	int fake_buflen;
	int timestamp_max_delta = 0;
	int have_timestamp = 0;
	sfx_timestamp_t start_timestamp; /* The timestamp at which the first frame will be played */
	sfx_timestamp_t min_timestamp;
	min_timestamp.secs = 0;
	sfx_timestamp_t timestamp;

	if (self->dev->get_output_timestamp)
		start_timestamp = self->dev->get_output_timestamp(self->dev);
	else {
		long sec, usec;
		sci_gettime(&sec, &usec);
		start_timestamp = sfx_new_timestamp(sec, usec, self->dev->conf.rate);
	}

	if ((P->outbuf) && (P->lastbuf_len)) {
		sfx_timestamp_t ts;
		int rv;

		if (P->have_outbuf_timestamp) {
			ts = sfx_timestamp_renormalise(P->outbuf_timestamp, self->dev->conf.rate);
		}

		rv = self->dev->output(self->dev, P->outbuf,
					   P->lastbuf_len,
					   (P->have_outbuf_timestamp)? &ts : NULL);

		if (rv == SFX_ERROR) {
			RELEASE_LOCK();
			return rv; /* error */
		}
	}

#if (DEBUG >= 1)
	if (self->feeds_nr)
		sciprintf("[soft-mixer] Mixing %d output frames on %d input feeds\n", buflen, self->feeds_nr);
#endif
	if (self->feeds_nr && !P->paused) {
		/* Below, we read out all feeds in case we have to skip frames first, then get the
		** most current sound. 'fake_buflen' is either the actual buflen (for the last iteration)
		** or a fraction of the buf length to discard.  */
		do {
			if (frames_skip) {
				if (frames_skip > self->dev->buf_size)
					fake_buflen = self->dev->buf_size;
				else
					fake_buflen = frames_skip;

				frames_skip -= fake_buflen;
			} else {
				fake_buflen = buflen;
				frames_skip = -1; /* Mark us as being completely done */
			}

			for (src_i = 0; src_i < self->feeds_nr; src_i++) {
				mix_compute_input_linear(self, src_i,
							 fake_buflen, &timestamp,
							 start_timestamp);

				if (timestamp.secs >= 0) {
					if (have_timestamp) {
						int diff = sfx_timestamp_usecs_diff(min_timestamp, timestamp);
						if (diff > 0) {
							/* New earlier timestamp */
							timestamp = min_timestamp;
							timestamp_max_delta += diff;
						} else if (diff > timestamp_max_delta)
							timestamp_max_delta = diff;
						/* New max delta for timestamp */
					} else {
						min_timestamp = timestamp;
						have_timestamp = 1;
					}
				}
			}
			/* Destroy all feeds we finished */
			for (src_i = 0; src_i < self->feeds_nr; src_i++)
				if (self->feeds[src_i].mode == SFX_PCM_FEED_MODE_DEAD)
					_mix_unsubscribe(self, self->feeds[src_i].feed);
		} while (frames_skip >= 0);

	} else { /* Zero it out */
		memset(P->compbuf_l, 0, sizeof(gint32) * buflen);
		memset(P->compbuf_r, 0, sizeof(gint32) * buflen);
	}

#if (DEBUG >= 1)
	if (self->feeds_nr)
		sciprintf("[soft-mixer] Done mixing for this session, the result will be our next output buffer\n");
#endif

#if (DEBUG >= 3)
	if (self->feeds_nr) {
		int i;
		sciprintf("[soft-mixer] Intermediate representation:\n");
		for (i = 0; i < buflen; i++)
			sciprintf("[soft-mixer] Offset %d:\t[%04x:%04x]\t%d:%d\n", i,
				  P->compbuf_l[i] & 0xffff, P->compbuf_r[i] & 0xffff,
				  P->compbuf_l[i], P->compbuf_r[i]);
	}
#endif

	if (timestamp_max_delta > TIMESTAMP_MAX_ALLOWED_DELTA)
		sciprintf("[soft-mixer] Warning: Difference in timestamps between audio feeds is %d us\n", timestamp_max_delta);

	mix_compute_output(self, buflen);
	P->lastbuf_len = buflen;

	/* Finalize */
	mix_swap_buffers(self);
	if (have_timestamp)
		P->outbuf_timestamp = sfx_timestamp_add(min_timestamp,
							timestamp_max_delta >> 1);
	P->have_outbuf_timestamp = have_timestamp;

}	RELEASE_LOCK();
	return SFX_OK;
}

static void
mix_pause(sfx_pcm_mixer_t *self)
{
	ACQUIRE_LOCK();
	P->paused = 1;
	RELEASE_LOCK();
}

static void
mix_resume(sfx_pcm_mixer_t *self)
{
	ACQUIRE_LOCK();
	P->paused = 0;
	RELEASE_LOCK();
}

sfx_pcm_mixer_t sfx_pcm_mixer_soft_linear = {
	"soft-linear",
	"0.1",

	mix_init,
	mix_exit,
	mix_subscribe,
	mix_pause,
	mix_resume,
	mix_process_linear,

	0,
	0,
	NULL,
	NULL,
	NULL
};