1 files changed, 44 insertions, 0 deletions
diff --git a/lib/i-ring.h b/lib/i-ring.h
new file mode 100644
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--- /dev/null
+++ b/lib/i-ring.h
@@ -0,0 +1,44 @@
+/* definitions for a simple ring buffer
+   Copyright (C) 2006, 2009-2022 Free Software Foundation, Inc.
+
+   This file is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Lesser General Public License as
+   published by the Free Software Foundation, either version 3 of the
+   License, or (at your option) any later version.
+
+   This file is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public License
+   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+#include <stdbool.h>
+#include "verify.h"
+
+enum { I_RING_SIZE = 4 };
+verify (1 <= I_RING_SIZE);
+
+/* When ir_empty is true, the ring is empty.
+   Otherwise, ir_data[B..F] are defined, where B..F is the contiguous
+   range of indices, modulo I_RING_SIZE, from back to front, inclusive.
+   Undefined elements of ir_data are always set to ir_default_val.
+   Popping from an empty ring aborts.
+   Pushing onto a full ring returns the displaced value.
+   An empty ring has F==B and ir_empty == true.
+   A ring with one entry still has F==B, but now ir_empty == false.  */
+struct I_ring
+{
+  int ir_data[I_RING_SIZE];
+  int ir_default_val;
+  unsigned int ir_front;
+  unsigned int ir_back;
+  bool ir_empty;
+};
+typedef struct I_ring I_ring;
+
+void i_ring_init (I_ring *ir, int ir_default_val);
+int i_ring_push (I_ring *ir, int val);
+int i_ring_pop (I_ring *ir);
+bool i_ring_empty (I_ring const *ir) _GL_ATTRIBUTE_PURE;