/* a simple ring buffer

   Copyright (C) 2006, 2009-2018 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 <https://www.gnu.org/licenses/>.  */

/* written by Jim Meyering */

#include <config.h>

#include "i-ring.h"

#include <stdlib.h>

void

i_ring_init (I_ring *ir, int default_val)

{

  int i;

  ir->ir_empty = true;

  ir->ir_front = 0;

  ir->ir_back = 0;

  for (i = 0; i < I_RING_SIZE; i++)

    ir->ir_data[i] = default_val;

  ir->ir_default_val = default_val;

}

bool

i_ring_empty (I_ring const *ir)

{

  return ir->ir_empty;

}

int

i_ring_push (I_ring *ir, int val)

{

  unsigned int dest_idx = (ir->ir_front + !ir->ir_empty) % I_RING_SIZE;

  int old_val = ir->ir_data[dest_idx];

  ir->ir_data[dest_idx] = val;

  ir->ir_front = dest_idx;

  if (dest_idx == ir->ir_back)

    ir->ir_back = (ir->ir_back + !ir->ir_empty) % I_RING_SIZE;

  ir->ir_empty = false;

  return old_val;

}

int

i_ring_pop (I_ring *ir)

{

  int top_val;

  if (i_ring_empty (ir))

    abort ();

  top_val = ir->ir_data[ir->ir_front];

  ir->ir_data[ir->ir_front] = ir->ir_default_val;

  if (ir->ir_front == ir->ir_back)

    ir->ir_empty = true;

  else

    ir->ir_front = ((ir->ir_front + I_RING_SIZE - 1) % I_RING_SIZE);

  return top_val;

}