/* definitions for a simple ring buffer

   Copyright (C) 2006, 2009-2017 Free Software Foundation, Inc.

   This program is free software: you can redistribute it and/or modify

   it under the terms of the GNU General Public License as published by

   the Free Software Foundation; either version 3 of the License, or

   (at your option) any later version.

   This program 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 General Public License for more details.

   You should have received a copy of the GNU General Public License

   along with this program.  If not, see <http://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;