lib/i-ring.c

   1 /* a simple ring buffer
   2    Copyright (C) 2006, 2009-2018 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 /* written by Jim Meyering */
  18
  19 #include <config.h>
  20 #include "i-ring.h"
  21
  22 #include <stdlib.h>
  23
  24 void
  25 i_ring_init (I_ring *ir, int default_val)
  26 {
  27   int i;
  28   ir->ir_empty = true;
  29   ir->ir_front = 0;
  30   ir->ir_back = 0;
  31   for (i = 0; i < I_RING_SIZE; i++)
  32     ir->ir_data[i] = default_val;
  33   ir->ir_default_val = default_val;
  34 }
  35
  36 bool
  37 i_ring_empty (I_ring const *ir)
  38 {
  39   return ir->ir_empty;
  40 }
  41
  42 int
  43 i_ring_push (I_ring *ir, int val)
  44 {
  45   unsigned int dest_idx = (ir->ir_front + !ir->ir_empty) % I_RING_SIZE;
  46   int old_val = ir->ir_data[dest_idx];
  47   ir->ir_data[dest_idx] = val;
  48   ir->ir_front = dest_idx;
  49   if (dest_idx == ir->ir_back)
  50     ir->ir_back = (ir->ir_back + !ir->ir_empty) % I_RING_SIZE;
  51   ir->ir_empty = false;
  52   return old_val;
  53 }
  54
  55 int
  56 i_ring_pop (I_ring *ir)
  57 {
  58   int top_val;
  59   if (i_ring_empty (ir))
  60     abort ();
  61   top_val = ir->ir_data[ir->ir_front];
  62   ir->ir_data[ir->ir_front] = ir->ir_default_val;
  63   if (ir->ir_front == ir->ir_back)
  64     ir->ir_empty = true;
  65   else
  66     ir->ir_front = ((ir->ir_front + I_RING_SIZE - 1) % I_RING_SIZE);
  67   return top_val;
  68 }