ring.h

 
#ifndef MPIX_RING_H
#define MPIX_RING_H
 
#include <stdbool.h>
#include <string.h>
 
struct mpix_ring {
    uint8_t *data;
    size_t size;
    size_t head;
    size_t tail;
    size_t peek;
    bool full;
};
 
static inline void mpix_ring_init(struct mpix_ring *ring, uint8_t *buf, size_t size)
{
    memset(ring, 0x00, sizeof(*ring));
    ring->data = buf;
    ring->size = size;
}
 
static inline bool mpix_ring_is_full(struct mpix_ring *ring)
{
    return ring->full;
}
 
static inline bool mpix_ring_is_empty(struct mpix_ring *ring)
{
    return ring->head == ring->tail && !ring->full;
}
 
static inline size_t mpix_ring_headroom(struct mpix_ring *ring)
{
    if (ring->head < ring->tail) {
        /* [::::H      T::::]
         *      ^^^^^^^
         */
        return ring->tail - ring->head;
    }
    if (ring->tail < ring->head) {
        /* [    T::::::H    ]
         *             ^^^^^
         */
        return ring->size - ring->head;
    }
    if (mpix_ring_is_empty(ring)) {
        /* [          TH    ]
         *             ^^^^^
         */
        return ring->size - ring->head;
    }
    return 0;
}
 
static inline size_t mpix_ring_tailroom(struct mpix_ring *ring)
{
    if (ring->head < ring->tail) {
        /* [::::H      T::::]
         *             ^^^^^
         */
        return ring->size - ring->tail;
    }
    if (ring->tail < ring->head) {
        /* [    T::::::H    ]
         *      ^^^^^^^
         */
        return ring->head - ring->tail;
    }
    if (mpix_ring_is_full(ring)) {
        /* [::::::::::HT::::]
         *             ^^^^^
         */
        return ring->size - ring->tail;
    }
    return 0;
}
 
static inline size_t mpix_ring_peekroom(struct mpix_ring *ring)
{
    if (ring->head < ring->tail && ring->tail < ring->peek) {
        /* [::::H      T:P::]
         *               ^^^
         */
        return ring->size - ring->peek;
    }
    if (ring->peek < ring->head && ring->head < ring->tail) {
        /* [:P::H      T::::]
         *   ^^^
         */
        return ring->head - ring->peek;
    }
    if (ring->tail < ring->peek && ring->peek < ring->head) {
        /* [    T:P::::H    ]
         *        ^^^^^
         */
        return ring->head - ring->peek;
    }
    if (mpix_ring_is_full(ring) && ring->tail <= ring->peek) {
        /* [::::::::::HT:P::]
         *               ^^^
         */
        return ring->size - ring->peek;
    }
    if (mpix_ring_is_full(ring) && ring->peek < ring->head) {
        /* [::P:::::::HT::::]
         *    ^^^^^^^^
         */
        return ring->head - ring->peek;
    }
    return 0;
}
 
static inline size_t mpix_ring_total_used(struct mpix_ring *ring)
{
    if (ring->head < ring->tail) {
        /* [::::H      T::::]
         *  ^^^^^      ^^^^^
         */
        return ring->head + ring->size - ring->tail;
    }
    if (ring->tail < ring->head) {
        /* [    T::::::H    ]
         *      ^^^^^^^^
         */
        return ring->head - ring->tail;
    }
    if (mpix_ring_is_full(ring)) {
        /* [::::::::::HT::::]
         *  ^^^^^^^^^^^^^^^^
         */
        return ring->size;
    }
    return 0;
}
 
static inline uint8_t *mpix_ring_write(struct mpix_ring *ring, size_t size)
{
    uint8_t *data = ring->data + ring->head;
 
    if (mpix_ring_headroom(ring) < size) {
        return NULL;
    }
    ring->head = (ring->head + size) % ring->size;
    ring->peek = ring->tail;
    ring->full = (ring->head == ring->tail);
    return data;
}
 
static inline uint8_t *mpix_ring_read(struct mpix_ring *ring, size_t size)
{
    uint8_t *data = ring->data + ring->tail;
 
    if (mpix_ring_tailroom(ring) < size) {
        return NULL;
    }
    ring->tail = (ring->tail + size) % ring->size;
    ring->peek = ring->tail;
    ring->full = 0;
    return data;
}
 
static inline uint8_t *mpix_ring_peek(struct mpix_ring *ring, size_t size)
{
    uint8_t *data = ring->data + ring->peek;
 
    if (mpix_ring_peekroom(ring) < size) {
        return NULL;
    }
    ring->peek = (ring->peek + size) % ring->size;
    return data;
}
 
#endif