1  /* a simple ring buffer
       2     Copyright (C) 2006, 2009-2023 Free Software Foundation, Inc.
       3  
       4     This file is free software: you can redistribute it and/or modify
       5     it under the terms of the GNU Lesser General Public License as
       6     published by the Free Software Foundation, either version 3 of the
       7     License, or (at your option) any later version.
       8  
       9     This file is distributed in the hope that it will be useful,
      10     but WITHOUT ANY WARRANTY; without even the implied warranty of
      11     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      12     GNU Lesser General Public License for more details.
      13  
      14     You should have received a copy of the GNU Lesser General Public License
      15     along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
      16  
      17  /* written by Jim Meyering */
      18  
      19  #include <config.h>
      20  #include "i-ring.h"
      21  
      22  #include <stdlib.h>
      23  
      24  void
      25  i_ring_init (I_ring *ir, int default_val)
      26  {
      27    int i;
      28    ir->ir_empty = true;
      29    ir->ir_front = 0;
      30    ir->ir_back = 0;
      31    for (i = 0; i < I_RING_SIZE; i++)
      32      ir->ir_data[i] = default_val;
      33    ir->ir_default_val = default_val;
      34  }
      35  
      36  bool
      37  i_ring_empty (I_ring const *ir)
      38  {
      39    return ir->ir_empty;
      40  }
      41  
      42  int
      43  i_ring_push (I_ring *ir, int val)
      44  {
      45    unsigned int dest_idx = (ir->ir_front + !ir->ir_empty) % I_RING_SIZE;
      46    int old_val = ir->ir_data[dest_idx];
      47    ir->ir_data[dest_idx] = val;
      48    ir->ir_front = dest_idx;
      49    if (dest_idx == ir->ir_back)
      50      ir->ir_back = (ir->ir_back + !ir->ir_empty) % I_RING_SIZE;
      51    ir->ir_empty = false;
      52    return old_val;
      53  }
      54  
      55  int
      56  i_ring_pop (I_ring *ir)
      57  {
      58    int top_val;
      59    if (i_ring_empty (ir))
      60      abort ();
      61    top_val = ir->ir_data[ir->ir_front];
      62    ir->ir_data[ir->ir_front] = ir->ir_default_val;
      63    if (ir->ir_front == ir->ir_back)
      64      ir->ir_empty = true;
      65    else
      66      ir->ir_front = ((ir->ir_front + I_RING_SIZE - 1) % I_RING_SIZE);
      67    return top_val;
      68  }