2 files changed, 99 insertions, 0 deletions

diff --git a/ring_buffer/ring_buffer.gpr b/ring_buffer/ring_buffer.gpr
new file mode 100644
index 0000000..bac706f
--- /dev/null
+++ b/ring_buffer/ring_buffer.gpr
@@ -0,0 +1,5 @@
+project Ring_Buffer is
+    for Source_Dirs use ("src");
+    for Object_Dir use "obj";
+    for Main use ("ring_buffer.adb");
+end Ring_Buffer;
diff --git a/ring_buffer/src/ring_buffer.adb b/ring_buffer/src/ring_buffer.adb
new file mode 100644
index 0000000..500ec5c
--- /dev/null
+++ b/ring_buffer/src/ring_buffer.adb
@@ -0,0 +1,94 @@
+with Ada.Text_IO; use Ada.Text_IO;
+
+procedure Ring_Buffer is
+
+  type Natural_Array is array (Natural range <>) of Integer;
+
+  type Ring_Buffer (Capacity : Natural) is record
+    Start_Index : Natural := 0; -- TODO: somehow make these 'mod Size'.
+    Cur_Index   : Natural := 0;
+    Empty       : Boolean := True;
+    -- TODO: the index type should be 'mod Size'.
+    -- TODO: 0 .. Capacity wastes 1 slot of space.
+    Buffer      : Natural_Array (0 .. Capacity) := (others => 0);
+  end record;
+
+  function Size (RB : Ring_Buffer) return Natural is
+  begin
+    if RB.Empty then
+      return 0;
+    elsif RB.Cur_Index = RB.Start_Index then
+      return RB.Capacity;
+    else
+      return (RB.Cur_Index - RB.Start_Index) mod RB.Capacity;
+    end if;
+  end Size;
+
+  function Push (RB : in out Ring_Buffer; Value : Integer) return Boolean is
+  begin
+    if Size (RB) = RB.Capacity then
+      return False;
+    else
+      RB.Buffer (RB.Cur_Index) := Value;
+      RB.Cur_Index := (RB.Cur_Index + 1) mod RB.Capacity;
+      RB.Empty := False;
+      return True;
+    end if;
+  end Push;
+
+  procedure Push (RB : in out Ring_Buffer; Value : Integer) is
+    unused : Boolean := Push (RB, Value);
+  begin
+    return;
+  end Push;
+
+  function Pop (RB : in out Ring_Buffer; Value : out Integer) return Boolean is
+  begin
+    if Size (RB) = 0 then
+      return False;
+    else
+      Value := RB.Buffer (RB.Start_Index);
+      RB.Start_Index := (RB.Start_Index + 1) mod RB.Capacity;
+      if RB.Start_Index = RB.Cur_Index then
+        RB.Empty := True;
+      end if;
+      return True;
+    end if;
+  end Pop;
+
+  procedure Pop (RB : in out Ring_Buffer) is
+    Dummy  : Integer;
+    unused : Boolean := Pop (RB, Dummy);
+  begin
+    return;
+  end Pop;
+
+  procedure Print (RB : Ring_Buffer) is
+  begin
+    Put ("[");
+    for I in 0 .. Size (RB) - 1 loop
+      Put (Integer'Image (RB.Buffer ((RB.Start_Index + I) mod RB.Capacity)));
+    end loop;
+    Put_Line ("]");
+  end Print;
+
+  Capacity : constant Natural := 5;
+  RB : Ring_Buffer (Capacity);
+
+begin
+  Push (RB, 1);
+  Push (RB, 2);
+  Push (RB, 3);
+  Push (RB, 4);
+  Push (RB, 5);
+  -- Full!
+  Push (RB, 6);
+  Push (RB, 7);
+  -- Make some space.
+  Pop (RB);
+  Pop (RB);
+  -- Push more.
+  Push (RB, 8);
+  Push (RB, 9);
+  Print (RB);
+end Ring_Buffer;