Implement custom ring buffer style queue

1 files changed, 43 insertions, 0 deletions

diff --git a/queue.adb b/queue.adb
new file mode 100644
index 0000000..a758224
--- /dev/null
+++ b/queue.adb
@@ -0,0 +1,43 @@
+with Ada.Unchecked_Deallocation;
+
+package body Queue is
+    procedure Delete_Items_Array is new Ada.Unchecked_Deallocation(Items_Array, Items_Array_Access);
+
+    procedure Grow(Q: in out Queue) is
+        New_Items: Items_Array_Access := new Items_Array(0..Q.Items'Length*2-1);
+    begin
+        for Offset in Q.Items'Range loop
+            New_Items(Offset) := Q.Items((Q.Start + Offset) mod Q.Items'Length);
+        end loop;
+        Delete_Items_Array(Q.Items);
+        Q.Items := New_Items;
+        Q.Start := 0;
+    end;
+
+    procedure Enqueue(Q: in out Queue; X: Item) is
+    begin
+        if Q.Items = null then
+            Q.Items := new Items_Array(0..INIT_CAPACITY-1);
+        end if;
+
+        if Q.Count >= Q.Items'Length then
+            Grow(Q);
+        end if;
+
+        Q.Items((Q.Start + Q.Count) mod Q.Items'Length) := X;
+        Q.Count := Q.Count + 1;
+    end;
+
+    function Dequeue(Q: in out Queue; X: out Item) return Boolean is
+    begin
+        if Q.Count <= 0 then
+            return False;
+        end if;
+
+        X := Q.Items(Q.Start);
+        Q.Start := (Q.Start + 1) mod Q.Items'Length;
+        Q.Count := Q.Count - 1;
+
+        return True;
+    end;
+end Queue;