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/*
* Copyright (C) 2016 Kaspar Schleiser <kaspar@schleiser.de>
* 2013 Freie Universität Berlin
*
* This file is subject to the terms and conditions of the GNU Lesser
* General Public License v2.1. See the file LICENSE in the top level
* directory for more details.
*/
/**
* @addtogroup core_util
* @{
*
* @file
* @brief Circular integer buffer interface
* @details This structure provides an organizational interface
* and combined with an memory array forms a circular buffer.
*
* @author Kaspar Schleiser <kaspar@schleiser.de>
*/
#ifndef CIB_H
#define CIB_H
#include "assert.h"
#ifdef __cplusplus
extern "C" {
#endif
/**
* @brief circular integer buffer structure
*/
typedef struct {
unsigned int read_count; /**< number of (successful) read accesses */
unsigned int write_count; /**< number of (successful) write accesses */
unsigned int mask; /**< Size of buffer -1, i.e. mask of the bits */
} cib_t;
/**
* @brief Initialize cib_t to a given size.
*/
#define CIB_INIT(SIZE) { 0, 0, (SIZE) - 1 }
/**
* @brief Initialize @p cib to 0 and set buffer size to @p size.
*
* @param[out] cib Buffer to initialize.
* Must not be NULL.
* @param[in] size Size of the buffer, must not exceed MAXINT/2.
* Should be equal to 0 or power of 2.
*/
static inline void cib_init(cib_t *__restrict cib, unsigned int size)
{
/* check if size is a power of 2 by comparing it to its complement */
assert(!(size & (size - 1)));
cib_t c = CIB_INIT(size);
*cib = c;
}
/**
* @brief Calculates difference between cib_put() and cib_get() accesses.
*
* @param[in] cib the cib_t to check.
* Must not be NULL.
* @return How often cib_get() can be called before @p cib is empty.
*/
static inline unsigned int cib_avail(const cib_t *cib)
{
return cib->write_count - cib->read_count;
}
/**
* @brief Check if cib is full.
*
* @param[in] cib the cib_t to check.
* Must not be NULL.
* @return 1 if cib_put() would return "-1", 0 otherwise
*/
static inline unsigned int cib_full(const cib_t *cib)
{
return ((int) cib_avail(cib)) > ((int) cib->mask);
}
/**
* @brief Get the index of the next item in buffer.
*
* @param[in,out] cib corresponding *cib* to buffer.
* Must not be NULL.
* @return index of next item, -1 if the buffer is empty
*/
static inline int cib_get(cib_t *__restrict cib)
{
if (cib->write_count > cib->read_count) {
return (int) (cib->read_count++ & cib->mask);
}
return -1;
}
/**
* @brief Get the index of the next item in buffer without removing it.
*
* @param[in,out] cib corresponding *cib* to buffer.
* Must not be NULL.
* @return index of next item, -1 if the buffer is empty
*/
static inline int cib_peek(cib_t *__restrict cib)
{
if (cib->write_count > cib->read_count) {
return (int) (cib->read_count & cib->mask);
}
return -1;
}
/**
* @brief Get the index of the next item in buffer.
*
* Unsafe version, *must not* be called if buffer is empty!
*
* @param[in,out] cib corresponding *cib* to buffer.
* Must not be NULL.
* @return index of next item
*/
static inline int cib_get_unsafe(cib_t *cib)
{
return (int) (cib->read_count++ & cib->mask);
}
/**
* @brief Get index for item in buffer to put to.
*
* @param[in,out] cib corresponding *cib* to buffer.
* Must not be NULL.
* @return index of item to put to, -1 if the buffer is full
*/
static inline int cib_put(cib_t *__restrict cib)
{
unsigned int avail = cib_avail(cib);
/* We use a signed compare, because the mask is -1u for an empty CIB. */
if ((int) avail <= (int) cib->mask) {
return (int) (cib->write_count++ & cib->mask);
}
return -1;
}
/**
* @brief Get index for item in buffer to put to.
*
* Unsafe version, *must not* be called if buffer is full!
*
* @param[in,out] cib corresponding *cib* to buffer.
* Must not be NULL.
* @return index of item to put to
*/
static inline int cib_put_unsafe(cib_t *cib)
{
return (int) (cib->write_count++ & cib->mask);
}
#ifdef __cplusplus
}
#endif
#endif /* CIB_H */
/** @} */