One design choice for ring buffer implementation is to distinguish
between full buffer and empty buffer. Traditional methods including
waste one entry for full (head + 1 == tail), or use
another flag for full. A new method is implemented as follow:
#define RING_LEN 16
#define RING_LIMIT (2 * RING_LEN - 1)
struct ring_entry
{
...
};
struct ring
{
int head;
int tail;
struct ring_entry entries[RING_LEN];
};
int ring_index(int n)
{
if (n > RING_LEN)
return n - RING_LEN;
else
return n;
};
int ring_get(struct ring *ring, struct ring_entry *entry)
{
/* empty */
if (ring->head == ring->tail)
return 0;
*entry = ring->entries[ring_index(ring->tail)];
ring->tail++;
if (ring->tail > RING_LIMIT)
ring->tail = 0;
return 1;
}
int ring_put(struct ring *ring, struct ring_entry *entry)
{
int ihead, itail;
ihead = ring_index(ring->head);
itail = ring_index(ring->tail);
/* full */
if (ihead == itail && ring->head != ring->tail)
return 0;
ring->entries[ihead] = *entry;
ring->head++;
if (ring->head > RING_LIMIT)
ring->head = 0;
return 1;
}
