ringbuf.c

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00001 /*
00002  * Copyright (c) 2008, Swedish Institute of Computer Science.
00003  * All rights reserved.
00004  *
00005  * Redistribution and use in source and binary forms, with or without
00006  * modification, are permitted provided that the following conditions
00007  * are met:
00008  * 1. Redistributions of source code must retain the above copyright
00009  *    notice, this list of conditions and the following disclaimer.
00010  * 2. Redistributions in binary form must reproduce the above copyright
00011  *    notice, this list of conditions and the following disclaimer in the
00012  *    documentation and/or other materials provided with the distribution.
00013  * 3. Neither the name of the Institute nor the names of its contributors
00014  *    may be used to endorse or promote products derived from this software
00015  *    without specific prior written permission.
00016  *
00017  * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
00018  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
00019  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
00020  * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
00021  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
00022  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
00023  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
00024  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
00025  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
00026  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
00027  * SUCH DAMAGE.
00028  *
00029  * This file is part of the Contiki operating system.
00030  *
00031  * $Id: ringbuf.c,v 1.2 2010/06/15 13:31:22 nifi Exp $
00032  */
00033 
00034 /**
00035  * \file
00036  *         Ring buffer library implementation
00037  * \author
00038  *         Adam Dunkels <adam@sics.se>
00039  */
00040 
00041 #include "lib/ringbuf.h"
00042 /*---------------------------------------------------------------------------*/
00043 void
00044 ringbuf_init(struct ringbuf *r, uint8_t *dataptr, uint8_t size)
00045 {
00046   r->data = dataptr;
00047   r->mask = size - 1;
00048   r->put_ptr = 0;
00049   r->get_ptr = 0;
00050 }
00051 /*---------------------------------------------------------------------------*/
00052 int
00053 ringbuf_put(struct ringbuf *r, uint8_t c)
00054 {
00055   /* Check if buffer is full. If it is full, return 0 to indicate that
00056      the element was not inserted into the buffer.
00057 
00058      XXX: there is a potential risk for a race condition here, because
00059      the ->get_ptr field may be written concurrently by the
00060      ringbuf_get() function. To avoid this, access to ->get_ptr must
00061      be atomic. We use an uint8_t type, which makes access atomic on
00062      most platforms, but C does not guarantee this.
00063   */
00064   if(((r->put_ptr - r->get_ptr) & r->mask) == r->mask) {
00065     return 0;
00066   }
00067   r->data[r->put_ptr] = c;
00068   r->put_ptr = (r->put_ptr + 1) & r->mask;
00069   return 1;
00070 }
00071 /*---------------------------------------------------------------------------*/
00072 int
00073 ringbuf_get(struct ringbuf *r)
00074 {
00075   uint8_t c;
00076   
00077   /* Check if there are bytes in the buffer. If so, we return the
00078      first one and increase the pointer. If there are no bytes left, we
00079      return -1.
00080 
00081      XXX: there is a potential risk for a race condition here, because
00082      the ->put_ptr field may be written concurrently by the
00083      ringbuf_put() function. To avoid this, access to ->get_ptr must
00084      be atomic. We use an uint8_t type, which makes access atomic on
00085      most platforms, but C does not guarantee this.
00086   */
00087   if(((r->put_ptr - r->get_ptr) & r->mask) > 0) {
00088     c = r->data[r->get_ptr];
00089     r->get_ptr = (r->get_ptr + 1) & r->mask;
00090     return c;
00091   } else {
00092     return -1;
00093   }
00094 }
00095 /*---------------------------------------------------------------------------*/
00096 int
00097 ringbuf_size(struct ringbuf *r)
00098 {
00099   return r->mask + 1;
00100 }
00101 /*---------------------------------------------------------------------------*/
00102 int
00103 ringbuf_elements(struct ringbuf *r)
00104 {
00105   return (r->put_ptr - r->get_ptr) & r->mask;
00106 }
00107 /*---------------------------------------------------------------------------*/

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