lib/i-ring.h

   1 /* definitions for a simple ring buffer
   2    Copyright (C) 2006, 2009-2021 Free Software Foundation, Inc.
   3
   4    This program is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 3 of the License, or
   7    (at your option) any later version.
   8
   9    This program 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 General Public License for more details.
  13
  14    You should have received a copy of the GNU 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;