src/seq/seq_midi_event.c

/**
 * \file seq/seq_midi_event.c
 * \brief MIDI byte <-> sequencer event coder
 * \author Takashi Iwai <tiwai@suse.de>
 * \author Jaroslav Kysela <perex@perex.cz>
 * \date 2000-2001
 */

/*
 *  MIDI byte <-> sequencer event coder
 *
 *  Copyright (C) 1998,99,2000 Takashi Iwai <tiwai@suse.de>,
 *			       Jaroslav Kysela <perex@perex.cz>
 *
 *
 *   This library is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU Lesser General Public License as
 *   published by the Free Software Foundation; either version 2.1 of
 *   the License, or (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU Lesser General Public License for more details.
 *
 *   You should have received a copy of the GNU Lesser General Public
 *   License along with this library; if not, write to the Free Software
 *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
 */

#include <malloc.h>
#include "local.h"

#ifndef DOC_HIDDEN

/* midi status */
struct snd_midi_event {
	size_t qlen;	/* queue length */
	size_t read;	/* chars read */
	int type;	/* current event type */
	unsigned char lastcmd;
	unsigned char nostat;
	size_t bufsize;
	unsigned char *buf;	/* input buffer */
};


/* event type, index into status_event[] */
/* from 0 to 6 are normal commands (note off, on, etc.) for 0x8?-0xe? */
#define ST_INVALID	7
#define ST_SPECIAL	8
#define ST_SYSEX	ST_SPECIAL
/* from 8 to 15 are events for 0xf0-0xf7 */


/* status event types */
typedef void (*event_encode_t)(snd_midi_event_t *dev, snd_seq_event_t *ev);
typedef void (*event_decode_t)(const snd_seq_event_t *ev, unsigned char *buf);

#endif /* DOC_HIDDEN */

/*
 * prototypes
 */
static void note_event(snd_midi_event_t *dev, snd_seq_event_t *ev);
static void one_param_ctrl_event(snd_midi_event_t *dev, snd_seq_event_t *ev);
static void pitchbend_ctrl_event(snd_midi_event_t *dev, snd_seq_event_t *ev);
static void two_param_ctrl_event(snd_midi_event_t *dev, snd_seq_event_t *ev);
static void one_param_event(snd_midi_event_t *dev, snd_seq_event_t *ev);
static void songpos_event(snd_midi_event_t *dev, snd_seq_event_t *ev);
static void note_decode(const snd_seq_event_t *ev, unsigned char *buf);
static void one_param_decode(const snd_seq_event_t *ev, unsigned char *buf);
static void pitchbend_decode(const snd_seq_event_t *ev, unsigned char *buf);
static void two_param_decode(const snd_seq_event_t *ev, unsigned char *buf);
static void songpos_decode(const snd_seq_event_t *ev, unsigned char *buf);

/*
 * event list
 */
#ifndef DOC_HIDDEN
static const struct status_event_list_t {
	int event;
	int qlen;
	event_encode_t encode;
	event_decode_t decode;
} status_event[] = {
	/* 0x80 - 0xef */
	{SND_SEQ_EVENT_NOTEOFF,		 2, note_event, note_decode},
	{SND_SEQ_EVENT_NOTEON,		 2, note_event, note_decode},
	{SND_SEQ_EVENT_KEYPRESS,	 2, note_event, note_decode},
	{SND_SEQ_EVENT_CONTROLLER,	 2, two_param_ctrl_event, two_param_decode},
	{SND_SEQ_EVENT_PGMCHANGE,	 1, one_param_ctrl_event, one_param_decode},
	{SND_SEQ_EVENT_CHANPRESS,	 1, one_param_ctrl_event, one_param_decode},
	{SND_SEQ_EVENT_PITCHBEND,	 2, pitchbend_ctrl_event, pitchbend_decode},
	/* invalid */
	{SND_SEQ_EVENT_NONE,		-1, NULL, NULL},
	/* 0xf0 - 0xff */
	{SND_SEQ_EVENT_SYSEX,		 1, NULL, NULL}, /* sysex: 0xf0 */
	{SND_SEQ_EVENT_QFRAME,		 1, one_param_event, one_param_decode}, /* 0xf1 */
	{SND_SEQ_EVENT_SONGPOS,		 2, songpos_event, songpos_decode}, /* 0xf2 */
	{SND_SEQ_EVENT_SONGSEL,		 1, one_param_event, one_param_decode}, /* 0xf3 */
	{SND_SEQ_EVENT_NONE,		-1, NULL, NULL}, /* 0xf4 */
	{SND_SEQ_EVENT_NONE,		-1, NULL, NULL}, /* 0xf5 */
	{SND_SEQ_EVENT_TUNE_REQUEST,	 0, NULL, NULL}, /* 0xf6 */
	{SND_SEQ_EVENT_NONE,		-1, NULL, NULL}, /* 0xf7 */
	{SND_SEQ_EVENT_CLOCK,		 0, NULL, NULL}, /* 0xf8 */
	{SND_SEQ_EVENT_NONE,		-1, NULL, NULL}, /* 0xf9 */
	{SND_SEQ_EVENT_START,		 0, NULL, NULL}, /* 0xfa */
	{SND_SEQ_EVENT_CONTINUE,	 0, NULL, NULL}, /* 0xfb */
	{SND_SEQ_EVENT_STOP, 		 0, NULL, NULL}, /* 0xfc */
	{SND_SEQ_EVENT_NONE, 		-1, NULL, NULL}, /* 0xfd */
	{SND_SEQ_EVENT_SENSING, 	 0, NULL, NULL}, /* 0xfe */
	{SND_SEQ_EVENT_RESET, 		 0, NULL, NULL}, /* 0xff */
};

static int extra_decode_ctrl14(snd_midi_event_t *dev, unsigned char *buf, int len, const snd_seq_event_t *ev);
static int extra_decode_xrpn(snd_midi_event_t *dev, unsigned char *buf, int count, const snd_seq_event_t *ev);

static const struct extra_event_list_t {
	int event;
	int (*decode)(snd_midi_event_t *dev, unsigned char *buf, int len, const snd_seq_event_t *ev);
} extra_event[] = {
	{SND_SEQ_EVENT_CONTROL14, extra_decode_ctrl14},
	{SND_SEQ_EVENT_NONREGPARAM, extra_decode_xrpn},
	{SND_SEQ_EVENT_REGPARAM, extra_decode_xrpn},
};

#define numberof(ary)	(sizeof(ary)/sizeof(ary[0]))
#endif /* DOC_HIDDEN */

/**
 * \brief Creates a MIDI event parser.
 * \param[in] bufsize Size of the buffer used for encoding; this should be
 *                    large enough to hold the largest MIDI message to be
 *                    encoded.
 * \param[out] rdev The new MIDI event parser.
 * \return Zero on success, otherwise a negative error code.
 *
 * This function creates and initializes a MIDI parser object that can be used
 * to convert a MIDI byte stream to sequencer events (encoding) and/or to
 * convert sequencer events to a MIDI byte stream (decoding).
 *
 * \par Errors:
 * <dl>
 * <dt>-ENOMEM<dd>Out of memory.
 *
 * \par Conforming to:
 * LSB 3.2
 */
int snd_midi_event_new(size_t bufsize, snd_midi_event_t **rdev)
{
	snd_midi_event_t *dev;

	*rdev = NULL;
	dev = (snd_midi_event_t *)calloc(1, sizeof(snd_midi_event_t));
	if (dev == NULL)
		return -ENOMEM;
	if (bufsize > 0) {
		dev->buf = malloc(bufsize);
		if (dev->buf == NULL) {
			free(dev);
			return -ENOMEM;
		}
	}
	dev->bufsize = bufsize;
	dev->lastcmd = 0xff;
	dev->type = ST_INVALID;
	*rdev = dev;
	return 0;
}

/**
 * \brief Frees a MIDI event parser.
 * \param dev MIDI event parser.
 *
 * Frees a MIDI event parser.
 *
 * \par Conforming to:
 * LSB 3.2
 */
void snd_midi_event_free(snd_midi_event_t *dev)
{
	if (dev != NULL) {
		free(dev->buf);
		free(dev);
	}
}

/**
 * \brief Enables/disables MIDI command merging.
 * \param dev MIDI event parser.
 * \param on 0 to enable MIDI command merging,
 *           1 to always write the command byte.
 *
 * This function enables or disables MIDI command merging (running status).
 *
 * When MIDI command merging is not disabled, #snd_midi_event_decode is allowed
 * to omit any status byte that is identical to the previous status byte.
 */
void snd_midi_event_no_status(snd_midi_event_t *dev, int on)
{
	dev->nostat = on ? 1 : 0;
}

/*
 * initialize record
 */
inline static void reset_encode(snd_midi_event_t *dev)
{
	dev->read = 0;
	dev->qlen = 0;
	dev->type = ST_INVALID;
}

/**
 * \brief Resets MIDI encode parser.
 * \param dev MIDI event parser.
 *
 * This function resets the MIDI encoder of the parser \a dev.
 * Any partially encoded MIDI message is dropped,
 * and running status state is cleared.
 *
 * \par Conforming to:
 * LSB 3.2
 */
void snd_midi_event_reset_encode(snd_midi_event_t *dev)
{
	reset_encode(dev);
}

/**
 * \brief Resets MIDI decode parser.
 * \param dev MIDI event parser.
 *
 * This function resets the MIDI decoder of the parser \a dev.
 * The next decoded message does not use running status from before the call to
 * \a snd_midi_event_reset_decode.
 *
 * \par Conforming to:
 * LSB 3.2
 */
void snd_midi_event_reset_decode(snd_midi_event_t *dev)
{
	dev->lastcmd = 0xff;
}

/**
 * \brief Resets MIDI encode/decode parsers.
 * \param dev MIDI event parser.
 *
 * This function resets both encoder and decoder of the MIDI event parser.
 * \sa snd_midi_event_reset_encode, snd_midi_event_reset_decode
 *
 * \par Conforming to:
 * LSB 3.2
 */
void snd_midi_event_init(snd_midi_event_t *dev)
{
	snd_midi_event_reset_encode(dev);
	snd_midi_event_reset_decode(dev);
}

/**
 * \brief Resizes the MIDI message encoding buffer.
 * \param dev MIDI event parser.
 * \param bufsize The new buffer size.
 * \return Zero on success, otherwise a negative error code.
 *
 * This function resizes the buffer that is used to hold partially encoded MIDI
 * messages.
 *
 * If there is a partially encoded message in the buffer, it is dropped.
 *
 * \par Errors:
 * <dl>
 * <dt>-ENOMEM<dd>Out of memory.
 *
 * \sa snd_midi_event_encode, snd_midi_event_reset_encode
 */
int snd_midi_event_resize_buffer(snd_midi_event_t *dev, size_t bufsize)
{
	unsigned char *new_buf, *old_buf;

	if (bufsize == dev->bufsize)
		return 0;
	new_buf = malloc(bufsize);
	if (new_buf == NULL)
		return -ENOMEM;
	old_buf = dev->buf;
	dev->buf = new_buf;
	dev->bufsize = bufsize;
	reset_encode(dev);
	free(old_buf);
	return 0;
}

/**
 * \brief Encodes bytes to sequencer event.
 * \param[in] dev MIDI event parser.
 * \param[in] buf Buffer containing bytes of a raw MIDI stream.
 * \param[in] count Number of bytes in \a buf.
 * \param[out] ev Sequencer event.
 * \return The number of bytes consumed, or a negative error code.
 *
 * This function tries to use up to \a count bytes from the beginning of the
 * buffer to encode a sequencer event.  If a complete MIDI message has been
 * encoded, the sequencer event is written to \a ev; otherwise, \a ev->type is
 * set to #SND_SEQ_EVENT_NONE, and further bytes are required to complete
 * a message.
 *
 * The buffer in \a dev is used to hold any bytes of a not-yet-complete MIDI
 * message.  If a System Exclusive message is larger than the buffer, the
 * message is split into multiple parts, and a sequencer event is returned at
 * the end of each part.
 *
 * Any bytes that are not part of a valid MIDI message are silently ignored,
 * i.e., they are consumed without signaling an error.
 *
 * When this function returns a system exclusive sequencer event (\a ev->type
 * is #SND_SEQ_EVENT_SYSEX), the data pointer (\a ev->data.ext.ptr) points into
 * the MIDI event parser's buffer.  Therefore, the sequencer event can only be
 * used as long as that buffer remains valid, i.e., until the next call to
 * #snd_midi_event_encode, #snd_midi_event_encode_byte,
 * #snd_midi_event_resize_buffer, #snd_midi_event_init,
 * #snd_midi_event_reset_encode, or #snd_midi_event_free for that MIDI event
 * parser.
 *
 * This function can generate any sequencer event that corresponds to a MIDI
 * message, i.e.:
 * - #SND_SEQ_EVENT_NOTEOFF
 * - #SND_SEQ_EVENT_NOTEON
 * - #SND_SEQ_EVENT_KEYPRESS
 * - #SND_SEQ_EVENT_CONTROLLER
 * - #SND_SEQ_EVENT_PGMCHANGE
 * - #SND_SEQ_EVENT_CHANPRESS
 * - #SND_SEQ_EVENT_PITCHBEND
 * - #SND_SEQ_EVENT_SYSEX
 * - #SND_SEQ_EVENT_QFRAME
 * - #SND_SEQ_EVENT_SONGPOS
 * - #SND_SEQ_EVENT_SONGSEL
 * - #SND_SEQ_EVENT_TUNE_REQUEST
 * - #SND_SEQ_EVENT_CLOCK
 * - #SND_SEQ_EVENT_START
 * - #SND_SEQ_EVENT_CONTINUE
 * - #SND_SEQ_EVENT_STOP
 * - #SND_SEQ_EVENT_SENSING
 * - #SND_SEQ_EVENT_RESET
 * .
 * Some implementations may also be able to generate the following events
 * for a sequence of controller change messages:
 * - #SND_SEQ_EVENT_CONTROL14
 * - #SND_SEQ_EVENT_NONREGPARAM
 * - #SND_SEQ_EVENT_REGPARAM
 *
 * \par Conforming to:
 * LSB 3.2
 *
 * \sa snd_midi_event_new, snd_midi_event_reset_encode, snd_midi_event_encode_byte
 */
long snd_midi_event_encode(snd_midi_event_t *dev, const unsigned char *buf, long count, snd_seq_event_t *ev)
{
	long result = 0;
	int rc;

	ev->type = SND_SEQ_EVENT_NONE;

	while (count-- > 0) {
		rc = snd_midi_event_encode_byte(dev, *buf++, ev);
		result++;
		if (rc < 0)
			return rc;
		else if (rc > 0)
			return result;
	}

	return result;
}

/**
 * \brief Encodes byte to sequencer event.
 * \param[in] dev MIDI event parser.
 * \param[in] c A byte of a raw MIDI stream.
 * \param[out] ev Sequencer event.
 * \return 1 if a sequenver event has been completed, 0 if more bytes are
 *         required to complete an event, or a negative error code.
 *
 * This function tries to use the byte \a c to encode a sequencer event.  If
 * a complete MIDI message has been encoded, the sequencer event is written to
 * \a ev; otherwise, further bytes are required to complete a message.
 *
 * See also the description of #snd_midi_event_encode.
 *
 * \par Conforming to:
 * LSB 3.2
 *
 * \sa snd_midi_event_new, snd_midi_event_reset_encode, snd_midi_event_encode
 */
int snd_midi_event_encode_byte(snd_midi_event_t *dev, int c, snd_seq_event_t *ev)
{
	int rc = 0;

	c &= 0xff;

	if (c >= MIDI_CMD_COMMON_CLOCK) {
		/* real-time event */
		ev->type = status_event[ST_SPECIAL + c - 0xf0].event;
		ev->flags &= ~SND_SEQ_EVENT_LENGTH_MASK;
		ev->flags |= SND_SEQ_EVENT_LENGTH_FIXED;
		return ev->type != SND_SEQ_EVENT_NONE;
	}

	if ((c & 0x80) &&
	    (c != MIDI_CMD_COMMON_SYSEX_END || dev->type != ST_SYSEX)) {
		/* new command */
		dev->buf[0] = c;
		if ((c & 0xf0) == 0xf0) /* system message */
			dev->type = (c & 0x0f) + ST_SPECIAL;
		else
			dev->type = (c >> 4) & 0x07;
		dev->read = 1;
		dev->qlen = status_event[dev->type].qlen;
	} else {
		if (dev->qlen > 0) {
			/* rest of command */
			dev->buf[dev->read++] = c;
			if (dev->type != ST_SYSEX)
				dev->qlen--;
		} else {
			/* running status */
			dev->buf[1] = c;
			dev->qlen = status_event[dev->type].qlen - 1;
			dev->read = 2;
		}
	}
	if (dev->qlen == 0) {
		ev->type = status_event[dev->type].event;
		ev->flags &= ~SND_SEQ_EVENT_LENGTH_MASK;
		ev->flags |= SND_SEQ_EVENT_LENGTH_FIXED;
		if (status_event[dev->type].encode) /* set data values */
			status_event[dev->type].encode(dev, ev);
		if (dev->type >= ST_SPECIAL)
			dev->type = ST_INVALID;
		rc = 1;
	} else 	if (dev->type == ST_SYSEX) {
		if (c == MIDI_CMD_COMMON_SYSEX_END ||
		    dev->read >= dev->bufsize) {
			ev->flags &= ~SND_SEQ_EVENT_LENGTH_MASK;
			ev->flags |= SND_SEQ_EVENT_LENGTH_VARIABLE;
			ev->type = SND_SEQ_EVENT_SYSEX;
			ev->data.ext.len = dev->read;
			ev->data.ext.ptr = dev->buf;
			if (c != MIDI_CMD_COMMON_SYSEX_END)
				dev->read = 0; /* continue to parse */
			else
				reset_encode(dev); /* all parsed */
			rc = 1;
		}
	}

	return rc;
}

/* encode note event */
static void note_event(snd_midi_event_t *dev, snd_seq_event_t *ev)
{
	ev->data.note.channel = dev->buf[0] & 0x0f;
	ev->data.note.note = dev->buf[1];
	ev->data.note.velocity = dev->buf[2];
}

/* encode one parameter controls */
static void one_param_ctrl_event(snd_midi_event_t *dev, snd_seq_event_t *ev)
{
	ev->data.control.channel = dev->buf[0] & 0x0f;
	ev->data.control.value = dev->buf[1];
}

/* encode pitch wheel change */
static void pitchbend_ctrl_event(snd_midi_event_t *dev, snd_seq_event_t *ev)
{
	ev->data.control.channel = dev->buf[0] & 0x0f;
	ev->data.control.value = (int)dev->buf[2] * 128 + (int)dev->buf[1] - 8192;
}

/* encode midi control change */
static void two_param_ctrl_event(snd_midi_event_t *dev, snd_seq_event_t *ev)
{
	ev->data.control.channel = dev->buf[0] & 0x0f;
	ev->data.control.param = dev->buf[1];
	ev->data.control.value = dev->buf[2];
}

/* encode one parameter value*/
static void one_param_event(snd_midi_event_t *dev, snd_seq_event_t *ev)
{
	ev->data.control.value = dev->buf[1];
}

/* encode song position */
static void songpos_event(snd_midi_event_t *dev, snd_seq_event_t *ev)
{
	ev->data.control.value = (int)dev->buf[2] * 128 + (int)dev->buf[1];
}

/**
 * \brief Decodes sequencer event to MIDI byte stream.
 * \param[in] dev MIDI event parser.
 * \param[out] buf Buffer for the resulting MIDI byte stream.
 * \param[in] count Number of bytes in \a buf.
 * \param[in] ev The sequencer event to decode.
 * \return The number of bytes written to \a buf, or a negative error code.
 *
 * This function tries to decode the sequencer event into one or more MIDI
 * messages, and writes the raw MIDI byte(s) into \a buf.
 *
 * The generated MIDI messages may use running status, unless disabled with
 * #snd_midi_event_no_status.
 *
 * The required buffer size for a sequencer event it as most 12 bytes, except
 * for System Exclusive events (\a ev->type == #SND_SEQ_EVENT_SYSEX) which can
 * have any length (as specified by \a ev->data.ext.len).
 *
 * The following sequencer events correspond to MIDI messages:
 * - #SND_SEQ_EVENT_NOTEOFF
 * - #SND_SEQ_EVENT_NOTEON
 * - #SND_SEQ_EVENT_KEYPRESS
 * - #SND_SEQ_EVENT_CONTROLLER
 * - #SND_SEQ_EVENT_PGMCHANGE
 * - #SND_SEQ_EVENT_CHANPRESS
 * - #SND_SEQ_EVENT_PITCHBEND
 * - #SND_SEQ_EVENT_SYSEX
 * - #SND_SEQ_EVENT_QFRAME
 * - #SND_SEQ_EVENT_SONGPOS
 * - #SND_SEQ_EVENT_SONGSEL
 * - #SND_SEQ_EVENT_TUNE_REQUEST
 * - #SND_SEQ_EVENT_CLOCK
 * - #SND_SEQ_EVENT_START
 * - #SND_SEQ_EVENT_CONTINUE
 * - #SND_SEQ_EVENT_STOP
 * - #SND_SEQ_EVENT_SENSING
 * - #SND_SEQ_EVENT_RESET
 * - #SND_SEQ_EVENT_CONTROL14
 * - #SND_SEQ_EVENT_NONREGPARAM
 * - #SND_SEQ_EVENT_REGPARAM
 *
 * \par Errors:
 * <dl>
 * <dt>-EINVAL<dd>\a ev is not a valid sequencer event.
 * <dt>-ENOENT<dd>The sequencer event does not correspond to one or more MIDI messages.
 * <dt>-ENOMEM<dd>The MIDI message(s) would not fit into \a count bytes.
 *
 * \par Conforming to:
 * LSB 3.2
 *
 * \sa snd_midi_event_reset_decode, snd_midi_event_no_status
 */
long snd_midi_event_decode(snd_midi_event_t *dev, unsigned char *buf, long count, const snd_seq_event_t *ev)
{
	int cmd;
	long qlen;
	unsigned int type;

	if (ev->type == SND_SEQ_EVENT_NONE)
		return -ENOENT;

	for (type = 0; type < numberof(status_event); type++) {
		if (ev->type == status_event[type].event)
			goto __found;
	}
	for (type = 0; type < numberof(extra_event); type++) {
		if (ev->type == extra_event[type].event)
			return extra_event[type].decode(dev, buf, count, ev);
	}
	return -ENOENT;

      __found:
	if (type >= ST_SPECIAL)
		cmd = 0xf0 + (type - ST_SPECIAL);
	else
		/* data.note.channel and data.control.channel is identical */
		cmd = 0x80 | (type << 4) | (ev->data.note.channel & 0x0f);


	if (cmd == MIDI_CMD_COMMON_SYSEX) {
		snd_midi_event_reset_decode(dev);
		qlen = ev->data.ext.len;
		if (count < qlen)
			return -ENOMEM;
		switch (ev->flags & SND_SEQ_EVENT_LENGTH_MASK) {
		case SND_SEQ_EVENT_LENGTH_FIXED:
			return -EINVAL;	/* invalid event */
		}
		memcpy(buf, ev->data.ext.ptr, qlen);
		return qlen;
	} else {
		unsigned char xbuf[4];

		if ((cmd & 0xf0) == 0xf0 || dev->lastcmd != cmd || dev->nostat) {
			dev->lastcmd = cmd;
			xbuf[0] = cmd;
			if (status_event[type].decode)
				status_event[type].decode(ev, xbuf + 1);
			qlen = status_event[type].qlen + 1;
		} else {
			if (status_event[type].decode)
				status_event[type].decode(ev, xbuf + 0);
			qlen = status_event[type].qlen;
		}
		if (count < qlen)
			return -ENOMEM;
		memcpy(buf, xbuf, qlen);
		return qlen;
	}
}


/* decode note event */
static void note_decode(const snd_seq_event_t *ev, unsigned char *buf)
{
	buf[0] = ev->data.note.note & 0x7f;
	buf[1] = ev->data.note.velocity & 0x7f;
}

/* decode one parameter controls */
static void one_param_decode(const snd_seq_event_t *ev, unsigned char *buf)
{
	buf[0] = ev->data.control.value & 0x7f;
}

/* decode pitch wheel change */
static void pitchbend_decode(const snd_seq_event_t *ev, unsigned char *buf)
{
	int value = ev->data.control.value + 8192;
	buf[0] = value & 0x7f;
	buf[1] = (value >> 7) & 0x7f;
}

/* decode midi control change */
static void two_param_decode(const snd_seq_event_t *ev, unsigned char *buf)
{
	buf[0] = ev->data.control.param & 0x7f;
	buf[1] = ev->data.control.value & 0x7f;
}

/* decode song position */
static void songpos_decode(const snd_seq_event_t *ev, unsigned char *buf)
{
	buf[0] = ev->data.control.value & 0x7f;
	buf[1] = (ev->data.control.value >> 7) & 0x7f;
}

/* decode 14bit control */
static int extra_decode_ctrl14(snd_midi_event_t *dev, unsigned char *buf, int count, const snd_seq_event_t *ev)
{
	unsigned char cmd;
	int idx = 0;

	cmd = MIDI_CMD_CONTROL|(ev->data.control.channel & 0x0f);
	if (ev->data.control.param < 32) {
		if (count < 4)
			return -ENOMEM;
		if (dev->nostat && count < 6)
			return -ENOMEM;
		if (cmd != dev->lastcmd || dev->nostat) {
			if (count < 5)
				return -ENOMEM;
			buf[idx++] = dev->lastcmd = cmd;
		}
		buf[idx++] = ev->data.control.param;
		buf[idx++] = (ev->data.control.value >> 7) & 0x7f;
		if (dev->nostat)
			buf[idx++] = cmd;
		buf[idx++] = ev->data.control.param + 32;
		buf[idx++] = ev->data.control.value & 0x7f;
	} else {
		if (count < 2)
			return -ENOMEM;
		if (cmd != dev->lastcmd || dev->nostat) {
			if (count < 3)
				return -ENOMEM;
			buf[idx++] = dev->lastcmd = cmd;
		}
		buf[idx++] = ev->data.control.param & 0x7f;
		buf[idx++] = ev->data.control.value & 0x7f;
	}
	return idx;
}

/* decode reg/nonreg param */
static int extra_decode_xrpn(snd_midi_event_t *dev, unsigned char *buf, int count, const snd_seq_event_t *ev)
{
	unsigned char cmd;
	const char *cbytes;
	static const char cbytes_nrpn[4] = { MIDI_CTL_NONREG_PARM_NUM_MSB,
				       MIDI_CTL_NONREG_PARM_NUM_LSB,
				       MIDI_CTL_MSB_DATA_ENTRY,
				       MIDI_CTL_LSB_DATA_ENTRY };
	static const char cbytes_rpn[4] =  { MIDI_CTL_REGIST_PARM_NUM_MSB,
				       MIDI_CTL_REGIST_PARM_NUM_LSB,
				       MIDI_CTL_MSB_DATA_ENTRY,
				       MIDI_CTL_LSB_DATA_ENTRY };
	unsigned char bytes[4];
	int idx = 0, i;

	if (count < 8)
		return -ENOMEM;
	if (dev->nostat && count < 12)
		return -ENOMEM;
	cmd = MIDI_CMD_CONTROL|(ev->data.control.channel & 0x0f);
	bytes[0] = (ev->data.control.param & 0x3f80) >> 7;
	bytes[1] = ev->data.control.param & 0x007f;
	bytes[2] = (ev->data.control.value & 0x3f80) >> 7;
	bytes[3] = ev->data.control.value & 0x007f;
	if (cmd != dev->lastcmd && !dev->nostat) {
		if (count < 9)
			return -ENOMEM;
		buf[idx++] = dev->lastcmd = cmd;
	}
	cbytes = ev->type == SND_SEQ_EVENT_NONREGPARAM ? cbytes_nrpn : cbytes_rpn;
	for (i = 0; i < 4; i++) {
		if (dev->nostat)
			buf[idx++] = dev->lastcmd = cmd;
		buf[idx++] = cbytes[i];
		buf[idx++] = bytes[i];
	}
	return idx;
}