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