ringbufindex.c

/*
 * Copyright (c) 2022, smartmx - smartmx@qq.com
 * Copyright (c) 2015, SICS Swedish ICT.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the Institute nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 */

#include "ringbufindex.h"

/* Initialize a ring buffer. The size must be a power of two */
void ringbufindex_init(struct ringbufindex *r, RINGBUF_INDEX_CONF_TYPE size)
{
    r->mask = size - 1;
    r->put_ptr = 0;
    r->get_ptr = 0;
}

/* Put one element to the ring buffer */
int ringbufindex_put(struct ringbufindex *r)
{
    /* Check if buffer is full. If it is full, return 0 to indicate that
       the element was not inserted.

       XXX: there is a potential risk for a race condition here, because
       the ->get_ptr field may be written concurrently by the
       ringbufindex_get() function. To avoid this, access to ->get_ptr must
       be atomic. We use an uint8_t type, which makes access atomic on
       most platforms, but C does not guarantee this.
     */
    if (((r->put_ptr - r->get_ptr) & r->mask) == r->mask)
    {
        return 0;
    }
    CC_ACCESS_NOW(RINGBUF_INDEX_CONF_TYPE, r->put_ptr) = (r->put_ptr + 1) & r->mask;
    return 1;
}

/* Check if there is space to put an element.
 * Return the index where the next element is to be added */
int ringbufindex_peek_put(const struct ringbufindex *r)
{
    /* Check if there are bytes in the buffer. If so, we return the
       first one. If there are no bytes left, we return -1.
     */
    if (((r->put_ptr - r->get_ptr) & r->mask) == r->mask)
    {
        return -1;
    }
    return r->put_ptr;
}

/* Remove the first element and return its index */
int ringbufindex_get(struct ringbufindex *r)
{
    int get_ptr;

    /* Check if there are bytes in the buffer. If so, we return the
       first one and increase the pointer. If there are no bytes left, we
       return -1.

       XXX: there is a potential risk for a race condition here, because
       the ->put_ptr field may be written concurrently by the
       ringbufindex_put() function. To avoid this, access to ->get_ptr must
       be atomic. We use an uint8_t type, which makes access atomic on
       most platforms, but C does not guarantee this.
     */
    if (((r->put_ptr - r->get_ptr) & r->mask) > 0)
    {
        get_ptr = r->get_ptr;
        CC_ACCESS_NOW(RINGBUF_INDEX_CONF_TYPE, r->get_ptr) = (r->get_ptr + 1) & r->mask;
        return get_ptr;
    }
    else
    {
        return -1;
    }
}

/* Return the index of the first element
 * (which will be removed if calling ringbufindex_get) */
int ringbufindex_peek_get(const struct ringbufindex *r)
{
    /* Check if there are bytes in the buffer. If so, we return the
       first one. If there are no bytes left, we return -1.
     */
    if (((r->put_ptr - r->get_ptr) & r->mask) > 0)
    {
        return r->get_ptr;
    }
    else
    {
        return -1;
    }
}

/* Return the ring buffer size */
int ringbufindex_size(const struct ringbufindex *r)
{
    return r->mask + 1;
}

/* Return the number of elements currently in the ring buffer */
int ringbufindex_elements(const struct ringbufindex *r)
{
    return (r->put_ptr - r->get_ptr) & r->mask;
}

/* Is the ring buffer full? */
int ringbufindex_full(const struct ringbufindex *r)
{
    return ((r->put_ptr - r->get_ptr) & r->mask) == r->mask;
}

/* Is the ring buffer empty? */
int ringbufindex_empty(const struct ringbufindex *r)
{
    return ringbufindex_elements(r) == 0;
}