Add rudimentary support for jump list (CTRL+{O,I})

1 files changed, 85 insertions, 0 deletions

diff --git a/ring-buffer.c b/ring-buffer.c
new file mode 100644
index 0000000..537fb90
--- /dev/null
+++ b/ring-buffer.c
@@ -0,0 +1,85 @@
+#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);
+}