Fix integer overflow in ring buffer

src/atomics.h

@@ -31,6 +31,10 @@ struct SoundIoAtomicFlag {
     std::atomic_flag x;
 };
 
+struct SoundIoAtomicULong {
+    std::atomic<unsigned long> x;
+};
+
 #define SOUNDIO_ATOMIC_LOAD(a) (a.x.load())
 #define SOUNDIO_ATOMIC_FETCH_ADD(a, delta) (a.x.fetch_add(delta))
 #define SOUNDIO_ATOMIC_STORE(a, value) (a.x.store(value))
@@ -59,6 +63,10 @@ struct SoundIoAtomicFlag {
     atomic_flag x;
 };
 
+struct SoundIoAtomicULong {
+    atomic_ulong x;
+};
+
 #define SOUNDIO_ATOMIC_LOAD(a) atomic_load(&a.x)
 #define SOUNDIO_ATOMIC_FETCH_ADD(a, delta) atomic_fetch_add(&a.x, delta)
 #define SOUNDIO_ATOMIC_STORE(a, value) atomic_store(&a.x, value)

src/ring_buffer.c

@@ -43,7 +43,7 @@ int soundio_ring_buffer_capacity(struct SoundIoRingBuffer *rb) {
 }
 
 char *soundio_ring_buffer_write_ptr(struct SoundIoRingBuffer *rb) {
-    long write_offset = SOUNDIO_ATOMIC_LOAD(rb->write_offset);
+    unsigned long write_offset = SOUNDIO_ATOMIC_LOAD(rb->write_offset);
     return rb->mem.address + (write_offset % rb->capacity);
 }
 
@@ -53,7 +53,7 @@ void soundio_ring_buffer_advance_write_ptr(struct SoundIoRingBuffer *rb, int cou
 }
 
 char *soundio_ring_buffer_read_ptr(struct SoundIoRingBuffer *rb) {
-    long read_offset = SOUNDIO_ATOMIC_LOAD(rb->read_offset);
+    unsigned long read_offset = SOUNDIO_ATOMIC_LOAD(rb->read_offset);
     return rb->mem.address + (read_offset % rb->capacity);
 }
 
@@ -65,8 +65,8 @@ void soundio_ring_buffer_advance_read_ptr(struct SoundIoRingBuffer *rb, int coun
 int soundio_ring_buffer_fill_count(struct SoundIoRingBuffer *rb) {
     // Whichever offset we load first might have a smaller value. So we load
     // the read_offset first.
-    long read_offset = SOUNDIO_ATOMIC_LOAD(rb->read_offset);
-    long write_offset = SOUNDIO_ATOMIC_LOAD(rb->write_offset);
+    unsigned long read_offset = SOUNDIO_ATOMIC_LOAD(rb->read_offset);
+    unsigned long write_offset = SOUNDIO_ATOMIC_LOAD(rb->write_offset);
     int count = write_offset - read_offset;
     assert(count >= 0);
     assert(count <= rb->capacity);
@@ -78,7 +78,7 @@ int soundio_ring_buffer_free_count(struct SoundIoRingBuffer *rb) {
 }
 
 void soundio_ring_buffer_clear(struct SoundIoRingBuffer *rb) {
-    long read_offset = SOUNDIO_ATOMIC_LOAD(rb->read_offset);
+    unsigned long read_offset = SOUNDIO_ATOMIC_LOAD(rb->read_offset);
     SOUNDIO_ATOMIC_STORE(rb->write_offset, read_offset);
 }
 

src/ring_buffer.h

@@ -13,8 +13,8 @@
 
 struct SoundIoRingBuffer {
     struct SoundIoOsMirroredMemory mem;
-    struct SoundIoAtomicLong write_offset;
-    struct SoundIoAtomicLong read_offset;
+    struct SoundIoAtomicULong write_offset;
+    struct SoundIoAtomicULong read_offset;
     int capacity;
 };