123 lines
4.6 KiB
C
123 lines
4.6 KiB
C
/*
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* Copyright (c) 2008, Swedish Institute of Computer Science.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the Institute nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* This file is part of the Contiki operating system.
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*
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*/
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/**
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* \file
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* Ring buffer library implementation
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* \author
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* Adam Dunkels <adam@sics.se>
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*/
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#include "lib/ringbuf.h"
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#include <sys/cc.h>
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/*---------------------------------------------------------------------------*/
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void
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ringbuf_init(struct ringbuf *r, uint8_t *dataptr, uint8_t size)
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{
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r->data = dataptr;
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r->mask = size - 1;
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r->put_ptr = 0;
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r->get_ptr = 0;
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}
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/*---------------------------------------------------------------------------*/
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int
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ringbuf_put(struct ringbuf *r, uint8_t c)
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{
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/* Check if buffer is full. If it is full, return 0 to indicate that
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the element was not inserted into the buffer.
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XXX: there is a potential risk for a race condition here, because
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the ->get_ptr field may be written concurrently by the
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ringbuf_get() function. To avoid this, access to ->get_ptr must
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be atomic. We use an uint8_t type, which makes access atomic on
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most platforms, but C does not guarantee this.
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*/
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if(((r->put_ptr - r->get_ptr) & r->mask) == r->mask) {
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return 0;
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}
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/*
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* CC_ACCESS_NOW is used because the compiler is allowed to reorder
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* the access to non-volatile variables.
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* In this case a reader might read from the moved index/ptr before
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* its value (c) is written. Reordering makes little sense, but
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* better safe than sorry.
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*/
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CC_ACCESS_NOW(uint8_t, r->data[r->put_ptr]) = c;
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CC_ACCESS_NOW(uint8_t, r->put_ptr) = (r->put_ptr + 1) & r->mask;
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return 1;
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}
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/*---------------------------------------------------------------------------*/
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int
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ringbuf_get(struct ringbuf *r)
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{
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uint8_t c;
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/* Check if there are bytes in the buffer. If so, we return the
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first one and increase the pointer. If there are no bytes left, we
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return -1.
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XXX: there is a potential risk for a race condition here, because
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the ->put_ptr field may be written concurrently by the
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ringbuf_put() function. To avoid this, access to ->get_ptr must
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be atomic. We use an uint8_t type, which makes access atomic on
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most platforms, but C does not guarantee this.
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*/
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if(((r->put_ptr - r->get_ptr) & r->mask) > 0) {
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/*
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* CC_ACCESS_NOW is used because the compiler is allowed to reorder
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* the access to non-volatile variables.
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* In this case the memory might be freed and overwritten by
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* increasing get_ptr before the value was copied to c.
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* Opposed to the put-operation this would even make sense,
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* because the register used for mask can be reused to save c
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* (on some architectures).
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*/
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c = CC_ACCESS_NOW(uint8_t, r->data[r->get_ptr]);
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CC_ACCESS_NOW(uint8_t, r->get_ptr) = (r->get_ptr + 1) & r->mask;
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return c;
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} else {
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return -1;
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}
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}
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/*---------------------------------------------------------------------------*/
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int
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ringbuf_size(struct ringbuf *r)
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{
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return r->mask + 1;
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}
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/*---------------------------------------------------------------------------*/
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int
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ringbuf_elements(struct ringbuf *r)
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{
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return (r->put_ptr - r->get_ptr) & r->mask;
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}
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/*---------------------------------------------------------------------------*/
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