lib/i-ring.h

   1 /* definitions for a simple ring buffer
   2    Copyright (C) 2006, 2009-2024 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;