Add generic circular buffer

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

app/meson.build

@@ -154,6 +154,9 @@ executable('scrcpy', src,
 ### TESTS
 
 tests = [
+    ['test_cbuf', [
+        'tests/test_cbuf.c',
+    ]],
     ['test_control_event_queue', [
         'tests/test_control_event_queue.c',
         'src/control_event.c'

app/src/cbuf.h

@@ -0,0 +1,50 @@
+// generic circular buffer (bounded queue) implementation
+#ifndef CBUF_H
+#define CBUF_H
+
+#include <stdbool.h>
+#include <unistd.h>
+
+// To define a circular buffer type of 20 ints:
+//     typedef CBUF(int, 20) my_cbuf_t;
+//
+// data has length CAP + 1 to distinguish empty vs full.
+#define CBUF(TYPE, CAP) { \
+    TYPE data[(CAP) + 1]; \
+    size_t head; \
+    size_t tail; \
+}
+
+#define cbuf_size_(PCBUF) \
+    (sizeof((PCBUF)->data) / sizeof(*(PCBUF)->data))
+
+#define cbuf_is_empty(PCBUF) \
+    ((PCBUF)->head == (PCBUF)->tail)
+
+#define cbuf_is_full(PCBUF) \
+    (((PCBUF)->head + 1) % cbuf_size_(PCBUF) == (PCBUF)->tail)
+
+#define cbuf_init(PCBUF) \
+    (void) ((PCBUF)->head = (PCBUF)->tail = 0)
+
+#define cbuf_push(PCBUF, ITEM) \
+    ({ \
+        bool ok = !cbuf_is_full(PCBUF); \
+        if (ok) { \
+            (PCBUF)->data[(PCBUF)->head] = (ITEM); \
+            (PCBUF)->head = ((PCBUF)->head + 1) % cbuf_size_(PCBUF); \
+        } \
+        ok; \
+    }) \
+
+#define cbuf_take(PCBUF, PITEM) \
+    ({ \
+        bool ok = !cbuf_is_empty(PCBUF); \
+        if (ok) { \
+            *(PITEM) = (PCBUF)->data[(PCBUF)->tail]; \
+            (PCBUF)->tail = ((PCBUF)->tail + 1) % cbuf_size_(PCBUF); \
+        } \
+        ok; \
+    })
+
+#endif

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;
+}