Ring buffer

auto_queue.h

/* 
 * Arthur Lapz <[email protected]>
 */
#ifndef ___AUTO_QUEUE_H___
#define ___AUTO_QUEUE_H___


#include <errno.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>


struct auto_queue {
	uint16_t	count;
	uint16_t	head;
	uint16_t	tail;
	uint16_t	size;
	uint16_t	nmemb;
	void		*ptr;
};


static inline void
auto_queue_init(struct auto_queue *self, void *ptr, uint16_t nmemb,
		uint16_t size)
{
	self->count = 0;
	self->head = 0;
	self->tail = 0;
	self->ptr = ptr;
	self->nmemb = nmemb;
	self->size = size;
}


static inline void *
auto_queue_init_alloc(struct auto_queue *self, uint16_t nmemb, uint16_t size)
{
	void *ptr = malloc(nmemb * size);
	if (ptr == NULL)
		return NULL;

	auto_queue_init(self, ptr, nmemb, size);
	return ptr;
}


static inline void
auto_queue_reset(struct auto_queue *self)
{
	self->head = 0;
	self->tail = 0;
	self->count = 0;
}


/*
 * sqe: submission pointer(head)
 */
static inline void *
auto_queue_sqe(struct auto_queue *self)
{
	const uint16_t size  = self->size;
	const uint16_t count = self->count;
	if (count == size)
		return NULL;

	uint16_t head   = self->head;
	void *const ret = &((uint8_t *)self->ptr)[self->nmemb * head];

	head++;

	if (head >= size)
		head = 0;

	self->head  = head;
	self->count = count +1u;

	return ret;
}
/* --- */


/*
 * cqe: completion pointer(tail)
 */
static inline void *
auto_queue_cqe_peek(struct auto_queue *self)
{
	if (self->count == 0)
		return NULL;

	return &((uint8_t *)self->ptr)[self->nmemb * self->tail];
}


static inline void
auto_queue_cqe_seen(struct auto_queue *self)
{
	uint16_t tail = self->tail +1u;
	if (tail >= (self->size))
		tail = 0;

	self->tail = tail;
	self->count--;
}


static inline void *
auto_queue_cqe(struct auto_queue *self)
{
	void *const ret = auto_queue_cqe_peek(self);
	if (ret == NULL)
		return NULL;

	auto_queue_cqe_seen(self);
	return ret;
}


#endif /* ___AUTO_QUEUE_H___ */