Add generic circular buffer

Add a circular buffer implementation, to factorize multiple specific
queues implementation.

app/tests/test_cbuf.c

@@ -0,0 +1,73 @@
+#include <assert.h>
+#include <string.h>
+
+#include "cbuf.h"
+
+struct int_queue CBUF(int, 32);
+
+static void test_cbuf_empty(void) {
+    struct int_queue queue;
+    cbuf_init(&queue);
+
+    assert(cbuf_is_empty(&queue));
+
+    bool push_ok = cbuf_push(&queue, 42);
+    assert(push_ok);
+    assert(!cbuf_is_empty(&queue));
+
+    int item;
+    bool take_ok = cbuf_take(&queue, &item);
+    assert(take_ok);
+    assert(cbuf_is_empty(&queue));
+
+    bool take_empty_ok = cbuf_take(&queue, &item);
+    assert(!take_empty_ok); // the queue is empty
+}
+
+static void test_cbuf_full(void) {
+    struct int_queue queue;
+    cbuf_init(&queue);
+
+    assert(!cbuf_is_full(&queue));
+
+    // fill the queue
+    for (int i = 0; i < 32; ++i) {
+        bool ok = cbuf_push(&queue, i);
+        assert(ok);
+    }
+    bool ok = cbuf_push(&queue, 42);
+    assert(!ok); // the queue if full
+
+    int item;
+    bool take_ok = cbuf_take(&queue, &item);
+    assert(take_ok);
+    assert(!cbuf_is_full(&queue));
+}
+
+static void test_cbuf_push_take(void) {
+    struct int_queue queue;
+    cbuf_init(&queue);
+
+    bool push1_ok = cbuf_push(&queue, 42);
+    assert(push1_ok);
+
+    bool push2_ok = cbuf_push(&queue, 35);
+    assert(push2_ok);
+
+    int item;
+
+    bool take1_ok = cbuf_take(&queue, &item);
+    assert(take1_ok);
+    assert(item == 42);
+
+    bool take2_ok = cbuf_take(&queue, &item);
+    assert(take2_ok);
+    assert(item == 35);
+}
+
+int main(void) {
+    test_cbuf_empty();
+    test_cbuf_full();
+    test_cbuf_push_take();
+    return 0;
+}