nes-proj/os/lib/ringbuf.c
2017-09-01 15:29:00 +02:00

124 lines
4.6 KiB
C

/*
* Copyright (c) 2008, Swedish Institute of Computer Science.
* 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.
*
* This file is part of the Contiki operating system.
*
*/
/**
* \file
* Ring buffer library implementation
* \author
* Adam Dunkels <adam@sics.se>
*/
#include "lib/ringbuf.h"
#include <sys/cc.h>
/*---------------------------------------------------------------------------*/
void
ringbuf_init(struct ringbuf *r, uint8_t *dataptr, uint8_t size)
{
r->data = dataptr;
r->mask = size - 1;
r->put_ptr = 0;
r->get_ptr = 0;
}
/*---------------------------------------------------------------------------*/
int
ringbuf_put(struct ringbuf *r, uint8_t c)
{
/* Check if buffer is full. If it is full, return 0 to indicate that
the element was not inserted into the buffer.
XXX: there is a potential risk for a race condition here, because
the ->get_ptr field may be written concurrently by the
ringbuf_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 is used because the compiler is allowed to reorder
* the access to non-volatile variables.
* In this case a reader might read from the moved index/ptr before
* its value (c) is written. Reordering makes little sense, but
* better safe than sorry.
*/
CC_ACCESS_NOW(uint8_t, r->data[r->put_ptr]) = c;
CC_ACCESS_NOW(uint8_t, r->put_ptr) = (r->put_ptr + 1) & r->mask;
return 1;
}
/*---------------------------------------------------------------------------*/
int
ringbuf_get(struct ringbuf *r)
{
uint8_t c;
/* 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
ringbuf_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) {
/*
* CC_ACCESS_NOW is used because the compiler is allowed to reorder
* the access to non-volatile variables.
* In this case the memory might be freed and overwritten by
* increasing get_ptr before the value was copied to c.
* Opposed to the put-operation this would even make sense,
* because the register used for mask can be reused to save c
* (on some architectures).
*/
c = CC_ACCESS_NOW(uint8_t, r->data[r->get_ptr]);
CC_ACCESS_NOW(uint8_t, r->get_ptr) = (r->get_ptr + 1) & r->mask;
return c;
} else {
return -1;
}
}
/*---------------------------------------------------------------------------*/
int
ringbuf_size(struct ringbuf *r)
{
return r->mask + 1;
}
/*---------------------------------------------------------------------------*/
int
ringbuf_elements(struct ringbuf *r)
{
return (r->put_ptr - r->get_ptr) & r->mask;
}
/*---------------------------------------------------------------------------*/