/*
  Copyright (C) 2000 Paul Davis
  Copyright (C) 2003 Rohan Drape
  Copyright (C) 2016 GRAME (renaming for internal use)

  This program 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 program; if not, write to the Free Software
  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

  ISO/POSIX C version of Paul Davis's lock free ringbuffer C++ code.
  This is safe for the case of one read thread and one write thread.
*/

#ifndef __ring_buffer__
#define __ring_buffer__

#include <stdlib.h>
#include <string.h>

#ifdef WIN32
# pragma warning (disable: 4334)
#else
# pragma GCC diagnostic ignored "-Wunused-function"
#endif

typedef struct {
    char *buf;
    size_t len;
}
ringbuffer_data_t;

typedef struct {
    char *buf;
    volatile size_t write_ptr;
    volatile size_t read_ptr;
    size_t	size;
    size_t	size_mask;
    int	mlocked;
}
ringbuffer_t;

static ringbuffer_t *ringbuffer_create(size_t sz);
static void ringbuffer_free(ringbuffer_t *rb);
static void ringbuffer_get_read_vector(const ringbuffer_t *rb,
                                         ringbuffer_data_t *vec);
static void ringbuffer_get_write_vector(const ringbuffer_t *rb,
                                          ringbuffer_data_t *vec);
static size_t ringbuffer_read(ringbuffer_t *rb, char *dest, size_t cnt);
static size_t ringbuffer_peek(ringbuffer_t *rb, char *dest, size_t cnt);
static void ringbuffer_read_advance(ringbuffer_t *rb, size_t cnt);
static size_t ringbuffer_read_space(const ringbuffer_t *rb);
static int ringbuffer_mlock(ringbuffer_t *rb);
static void ringbuffer_reset(ringbuffer_t *rb);
static void ringbuffer_reset_size (ringbuffer_t * rb, size_t sz);
static size_t ringbuffer_write(ringbuffer_t *rb, const char *src,
                                 size_t cnt);
static void ringbuffer_write_advance(ringbuffer_t *rb, size_t cnt);
static size_t ringbuffer_write_space(const ringbuffer_t *rb);

/* Create a new ringbuffer to hold at least `sz' bytes of data. The
   actual buffer size is rounded up to the next power of two. */

static ringbuffer_t *
ringbuffer_create (size_t sz)
{
	size_t power_of_two;
	ringbuffer_t *rb;

	if ((rb = (ringbuffer_t *) malloc (sizeof (ringbuffer_t))) == NULL) {
		return NULL;
	}

	for (power_of_two = 1u; 1u << power_of_two < sz; power_of_two++);

	rb->size = 1u << power_of_two;
	rb->size_mask = rb->size;
	rb->size_mask -= 1;
	rb->write_ptr = 0;
	rb->read_ptr = 0;
	if ((rb->buf = (char *) malloc (rb->size)) == NULL) {
		free (rb);
		return NULL;
	}
	rb->mlocked = 0;

	return rb;
}

/* Free all data associated with the ringbuffer `rb'. */

static void
ringbuffer_free (ringbuffer_t * rb)
{
#ifdef USE_MLOCK
	if (rb->mlocked) {
		munlock (rb->buf, rb->size);
	}
#endif /* USE_MLOCK */
	free (rb->buf);
	free (rb);
}

/* Lock the data block of `rb' using the system call 'mlock'.  */

static int
ringbuffer_mlock (ringbuffer_t * rb)
{
#ifdef USE_MLOCK
	if (mlock (rb->buf, rb->size)) {
		return -1;
	}
#endif /* USE_MLOCK */
	rb->mlocked = 1;
	return 0;
}

/* Reset the read and write pointers to zero. This is not thread
   safe. */

static void
ringbuffer_reset (ringbuffer_t * rb)
{
	rb->read_ptr = 0;
	rb->write_ptr = 0;
    memset(rb->buf, 0, rb->size);
}

/* Reset the read and write pointers to zero. This is not thread
   safe. */

static void
ringbuffer_reset_size (ringbuffer_t * rb, size_t sz)
{
    rb->size = sz;
    rb->size_mask = rb->size;
    rb->size_mask -= 1;
    rb->read_ptr = 0;
    rb->write_ptr = 0;
}

/* Return the number of bytes available for reading. This is the
   number of bytes in front of the read pointer and behind the write
   pointer.  */

static size_t
ringbuffer_read_space (const ringbuffer_t * rb)
{
	size_t w, r;

	w = rb->write_ptr;
	r = rb->read_ptr;

	if (w > r) {
		return w - r;
	} else {
		return (w - r + rb->size) & rb->size_mask;
	}
}

/* Return the number of bytes available for writing. This is the
   number of bytes in front of the write pointer and behind the read
   pointer.  */

static size_t
ringbuffer_write_space (const ringbuffer_t * rb)
{
	size_t w, r;

	w = rb->write_ptr;
	r = rb->read_ptr;

	if (w > r) {
		return ((r - w + rb->size) & rb->size_mask) - 1;
	} else if (w < r) {
		return (r - w) - 1;
	} else {
		return rb->size - 1;
	}
}

/* The copying data reader. Copy at most `cnt' bytes from `rb' to
   `dest'.  Returns the actual number of bytes copied. */

static size_t
ringbuffer_read (ringbuffer_t * rb, char *dest, size_t cnt)
{
	size_t free_cnt;
	size_t cnt2;
	size_t to_read;
	size_t n1, n2;

	if ((free_cnt = ringbuffer_read_space (rb)) == 0) {
		return 0;
	}

	to_read = cnt > free_cnt ? free_cnt : cnt;

	cnt2 = rb->read_ptr + to_read;

	if (cnt2 > rb->size) {
		n1 = rb->size - rb->read_ptr;
		n2 = cnt2 & rb->size_mask;
	} else {
		n1 = to_read;
		n2 = 0;
	}

	memcpy (dest, &(rb->buf[rb->read_ptr]), n1);
	rb->read_ptr = (rb->read_ptr + n1) & rb->size_mask;

	if (n2) {
		memcpy (dest + n1, &(rb->buf[rb->read_ptr]), n2);
		rb->read_ptr = (rb->read_ptr + n2) & rb->size_mask;
	}

	return to_read;
}

/* The copying data reader w/o read pointer advance. Copy at most
   `cnt' bytes from `rb' to `dest'.  Returns the actual number of bytes
   copied. */

static size_t
ringbuffer_peek (ringbuffer_t * rb, char *dest, size_t cnt)
{
	size_t free_cnt;
	size_t cnt2;
	size_t to_read;
	size_t n1, n2;
	size_t tmp_read_ptr;

	tmp_read_ptr = rb->read_ptr;

	if ((free_cnt = ringbuffer_read_space (rb)) == 0) {
		return 0;
	}

	to_read = cnt > free_cnt ? free_cnt : cnt;

	cnt2 = tmp_read_ptr + to_read;

	if (cnt2 > rb->size) {
		n1 = rb->size - tmp_read_ptr;
		n2 = cnt2 & rb->size_mask;
	} else {
		n1 = to_read;
		n2 = 0;
	}

	memcpy (dest, &(rb->buf[tmp_read_ptr]), n1);
	tmp_read_ptr = (tmp_read_ptr + n1) & rb->size_mask;

	if (n2) {
		memcpy (dest + n1, &(rb->buf[tmp_read_ptr]), n2);
	}

	return to_read;
}

/* The copying data writer. Copy at most `cnt' bytes to `rb' from
   `src'.  Returns the actual number of bytes copied. */

static size_t
ringbuffer_write (ringbuffer_t * rb, const char *src, size_t cnt)
{
	size_t free_cnt;
	size_t cnt2;
	size_t to_write;
	size_t n1, n2;

	if ((free_cnt = ringbuffer_write_space (rb)) == 0) {
		return 0;
	}

	to_write = cnt > free_cnt ? free_cnt : cnt;

	cnt2 = rb->write_ptr + to_write;

	if (cnt2 > rb->size) {
		n1 = rb->size - rb->write_ptr;
		n2 = cnt2 & rb->size_mask;
	} else {
		n1 = to_write;
		n2 = 0;
	}

	memcpy (&(rb->buf[rb->write_ptr]), src, n1);
	rb->write_ptr = (rb->write_ptr + n1) & rb->size_mask;

	if (n2) {
		memcpy (&(rb->buf[rb->write_ptr]), src + n1, n2);
		rb->write_ptr = (rb->write_ptr + n2) & rb->size_mask;
	}

	return to_write;
}

/* Advance the read pointer `cnt' places. */

static void
ringbuffer_read_advance (ringbuffer_t * rb, size_t cnt)
{
	size_t tmp = (rb->read_ptr + cnt) & rb->size_mask;
	rb->read_ptr = tmp;
}

/* Advance the write pointer `cnt' places. */

static void
ringbuffer_write_advance (ringbuffer_t * rb, size_t cnt)
{
	size_t tmp = (rb->write_ptr + cnt) & rb->size_mask;
	rb->write_ptr = tmp;
}

/* The non-copying data reader. `vec' is an array of two places. Set
   the values at `vec' to hold the current readable data at `rb'. If
   the readable data is in one segment the second segment has zero
   length. */

static void
ringbuffer_get_read_vector (const ringbuffer_t * rb,
				 ringbuffer_data_t * vec)
{
	size_t free_cnt;
	size_t cnt2;
	size_t w, r;

	w = rb->write_ptr;
	r = rb->read_ptr;

	if (w > r) {
		free_cnt = w - r;
	} else {
		free_cnt = (w - r + rb->size) & rb->size_mask;
	}

	cnt2 = r + free_cnt;

	if (cnt2 > rb->size) {

		/* Two part vector: the rest of the buffer after the current write
		   ptr, plus some from the start of the buffer. */

		vec[0].buf = &(rb->buf[r]);
		vec[0].len = rb->size - r;
		vec[1].buf = rb->buf;
		vec[1].len = cnt2 & rb->size_mask;

	} else {

		/* Single part vector: just the rest of the buffer */

		vec[0].buf = &(rb->buf[r]);
		vec[0].len = free_cnt;
		vec[1].len = 0;
	}
}

/* The non-copying data writer. `vec' is an array of two places. Set
   the values at `vec' to hold the current writeable data at `rb'. If
   the writeable data is in one segment the second segment has zero
   length. */

static void
ringbuffer_get_write_vector (const ringbuffer_t * rb,
				  ringbuffer_data_t * vec)
{
	size_t free_cnt;
	size_t cnt2;
	size_t w, r;

	w = rb->write_ptr;
	r = rb->read_ptr;

	if (w > r) {
		free_cnt = ((r - w + rb->size) & rb->size_mask) - 1;
	} else if (w < r) {
		free_cnt = (r - w) - 1;
	} else {
		free_cnt = rb->size - 1;
	}

	cnt2 = w + free_cnt;

	if (cnt2 > rb->size) {

		/* Two part vector: the rest of the buffer after the current write
		   ptr, plus some from the start of the buffer. */

		vec[0].buf = &(rb->buf[w]);
		vec[0].len = rb->size - w;
		vec[1].buf = rb->buf;
		vec[1].len = cnt2 & rb->size_mask;
	} else {
		vec[0].buf = &(rb->buf[w]);
		vec[0].len = free_cnt;
		vec[1].len = 0;
	}
}

#endif // __ring_buffer__
