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#include "ring-buffer.h"
#include <stdlib.h>
struct RingBuffer {
int cur; /* index of current element, last added etc. */
int start; /* index of first/oldest element */
int end; /* index of reserved/empty slot */
size_t size; /* buffer capacity / number of slots */
bool iterating; /* whether we are in a sequence of prev/next calls */
const void *data[]; /* user supplied buffer content */
};
static int ringbuf_index_prev(RingBuffer *buf, int i) {
return (i-1+buf->size) % buf->size;
}
static int ringbuf_index_next(RingBuffer *buf, int i) {
return (i+1) % buf->size;
}
static bool ringbuf_isfull(RingBuffer *buf) {
return ringbuf_index_next(buf, buf->end) == buf->start;
}
static bool ringbuf_isempty(RingBuffer *buf) {
return buf->start == buf->end;
}
static bool ringbuf_isfirst(RingBuffer *buf) {
return buf->cur == buf->start;
}
static bool ringbuf_islast(RingBuffer *buf) {
return ringbuf_index_next(buf, buf->cur) == buf->end;
}
const void *ringbuf_prev(RingBuffer *buf) {
if (ringbuf_isempty(buf) || (ringbuf_isfirst(buf) && buf->iterating))
return NULL;
if (buf->iterating)
buf->cur = ringbuf_index_prev(buf, buf->cur);
buf->iterating = true;
return buf->data[buf->cur];
}
const void *ringbuf_next(RingBuffer *buf) {
if (ringbuf_isempty(buf) || ringbuf_islast(buf))
return NULL;
buf->cur = ringbuf_index_next(buf, buf->cur);
buf->iterating = true;
return buf->data[buf->cur];
}
void ringbuf_add(RingBuffer *buf, const void *value) {
if (ringbuf_isempty(buf)) {
buf->end = ringbuf_index_next(buf, buf->end);
} else if (!ringbuf_islast(buf)) {
buf->cur = ringbuf_index_next(buf, buf->cur);
buf->end = ringbuf_index_next(buf, buf->cur);
} else if (ringbuf_isfull(buf)) {
buf->start = ringbuf_index_next(buf, buf->start);
buf->cur = ringbuf_index_next(buf, buf->cur);
buf->end = ringbuf_index_next(buf, buf->end);
} else {
buf->cur = ringbuf_index_next(buf, buf->cur);
buf->end = ringbuf_index_next(buf, buf->end);
}
buf->data[buf->cur] = value;
buf->iterating = false;
}
void ringbuf_invalidate(RingBuffer *buf) {
buf->iterating = false;
}
RingBuffer *ringbuf_alloc(size_t size) {
RingBuffer *buf;
if ((buf = calloc(1, sizeof(*buf) + (++size)*sizeof(buf->data[0]))))
buf->size = size;
return buf;
}
void ringbuf_free(RingBuffer *buf) {
free(buf);
}
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