1  /* definitions for a simple ring buffer
       2     Copyright (C) 2006, 2009-2022 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  #include <stdbool.h>
      18  #include "verify.h"
      19  
      20  enum { I_RING_SIZE = 4 };
      21  verify (1 <= I_RING_SIZE);
      22  
      23  /* When ir_empty is true, the ring is empty.
      24     Otherwise, ir_data[B..F] are defined, where B..F is the contiguous
      25     range of indices, modulo I_RING_SIZE, from back to front, inclusive.
      26     Undefined elements of ir_data are always set to ir_default_val.
      27     Popping from an empty ring aborts.
      28     Pushing onto a full ring returns the displaced value.
      29     An empty ring has F==B and ir_empty == true.
      30     A ring with one entry still has F==B, but now ir_empty == false.  */
      31  struct I_ring
      32  {
      33    int ir_data[I_RING_SIZE];
      34    int ir_default_val;
      35    unsigned int ir_front;
      36    unsigned int ir_back;
      37    bool ir_empty;
      38  };
      39  typedef struct I_ring I_ring;
      40  
      41  void i_ring_init (I_ring *ir, int ir_default_val);
      42  int i_ring_push (I_ring *ir, int val);
      43  int i_ring_pop (I_ring *ir);
      44  bool i_ring_empty (I_ring const *ir) _GL_ATTRIBUTE_PURE;