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/**
* @file ring_buffer.h
* @brief Simple circular buffer
*
* This implementation is not thread-safe. In particular, none of
* these functions are guaranteed re-entrant.
*/
#ifndef _RING_BUFFER_H_
#define _RING_BUFFER_H_
#ifdef __cplusplus
extern "C"{
#endif
/* The buffer is empty when head == tail.
*
* The buffer is full when the head is one byte in front of the tail,
* modulo buffer length.
*
* One byte is left free to distinguish empty from full. */
typedef struct ring_buffer {
/** Buffer items are stored into */
volatile uint8 *buf;
/** Index of the next item to remove */
uint16 head;
/** Index where the next item will get inserted */
uint16 tail;
/** Buffer capacity minus one */
uint16 size;
} ring_buffer;
/**
* Initialise a ring buffer.
*
* @param rb Instance to initialise
*
* @param size Number of items in buf. The ring buffer will always
* leave one element unoccupied, so the maximum number of
* elements it can store will be size - 1. Thus, size
* must be at least 2.
*
* @param buf Buffer to store items into
*/
__attribute__((unused))
static void rb_init(ring_buffer *rb, uint16 size, uint8 *buf) {
rb->head = 0;
rb->tail = 0;
rb->size = size - 1;
rb->buf = buf;
}
/** Return the number of elements stored in the ring buffer. */
static inline uint16 rb_full_count(ring_buffer *rb) {
volatile ring_buffer *arb = rb;
int32 size = arb->tail - arb->head;
if (arb->tail < arb->head) {
size += arb->size + 1;
}
return (uint16)size;
}
/** Return true if and only if the ring buffer is full. */
static inline int rb_is_full(ring_buffer *rb) {
return (rb->tail + 1 == rb->head) ||
(rb->tail == rb->size && rb->head == 0);
}
/** Append element onto the end of the ring buffer. */
static inline void rb_insert(ring_buffer *rb, uint8 element) {
rb->buf[rb->tail] = element;
rb->tail = (rb->tail == rb->size) ? 0 : rb->tail + 1;
}
/** Remove and return the first item from the ring buffer. */
static inline uint8 rb_remove(ring_buffer *rb) {
uint8 ch = rb->buf[rb->head];
rb->head = (rb->head == rb->size) ? 0 : rb->head + 1;
return ch;
}
/**
* If rb is not full, appends element and returns true; otherwise,
* does nothing and returns false. */
static inline int rb_safe_insert(ring_buffer *rb, uint8 element) {
if (rb_is_full(rb)) {
return 0;
}
rb_insert(rb, element);
return 1;
}
/**
* Append an item onto the end of a non-full ring buffer. If the
* buffer is full, removes its first item, then inserts the new
* element at the end.
*
* On success, returns -1. If an element was popped, returns the
* popped value. */
static inline int rb_push_insert(ring_buffer *rb, uint8 element) {
int ret = -1;
if (rb_is_full(rb)) {
ret = rb_remove(rb);
}
rb_insert(rb, element);
return ret;
}
/** Discard all items from the buffer */
static inline void rb_reset(ring_buffer *rb) {
rb->tail = rb->head;
}
#ifdef __cplusplus
} // extern "C"
#endif
#endif
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