1 /* definitions for a simple ring buffer 2 Copyright (C) 2006, 2009-2021 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;