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 #ifdef __cplusplus
  24 extern "C" {
  25 #endif
  26
  27
  28 enum { I_RING_SIZE = 4 };
  29 static_assert (1 <= I_RING_SIZE);
  30
  31 /* When ir_empty is true, the ring is empty.
  32    Otherwise, ir_data[B..F] are defined, where B..F is the contiguous
  33    range of indices, modulo I_RING_SIZE, from back to front, inclusive.
  34    Undefined elements of ir_data are always set to ir_default_val.
  35    Popping from an empty ring aborts.
  36    Pushing onto a full ring returns the displaced value.
  37    An empty ring has F==B and ir_empty == true.
  38    A ring with one entry still has F==B, but now ir_empty == false.  */
  39 struct I_ring
  40 {
  41   int ir_data[I_RING_SIZE];
  42   int ir_default_val;
  43   unsigned int ir_front;
  44   unsigned int ir_back;
  45   bool ir_empty;
  46 };
  47 typedef struct I_ring I_ring;
  48
  49 void i_ring_init (I_ring *ir, int ir_default_val);
  50 int i_ring_push (I_ring *ir, int val);
  51 int i_ring_pop (I_ring *ir);
  52 bool i_ring_empty (I_ring const *ir) _GL_ATTRIBUTE_PURE;
  53
  54
  55 #ifdef __cplusplus
  56 }
  57 #endif