/**************************************************************************/
/*                                                                        */
/*  The Why platform for program certification                            */
/*                                                                        */
/*  Copyright (C) 2002-2014                                               */
/*                                                                        */
/*    Jean-Christophe FILLIATRE, CNRS & Univ. Paris-sud                   */
/*    Claude MARCHE, INRIA & Univ. Paris-sud                              */
/*    Yannick MOY, Univ. Paris-sud                                        */
/*    Romain BARDOU, Univ. Paris-sud                                      */
/*                                                                        */
/*  Secondary contributors:                                               */
/*                                                                        */
/*    Thierry HUBERT, Univ. Paris-sud  (former Caduceus front-end)        */
/*    Nicolas ROUSSET, Univ. Paris-sud (on Jessie & Krakatoa)             */
/*    Ali AYAD, CNRS & CEA Saclay      (floating-point support)           */
/*    Sylvie BOLDO, INRIA              (floating-point support)           */
/*    Jean-Francois COUCHOT, INRIA     (sort encodings, hyps pruning)     */
/*    Mehdi DOGGUY, Univ. Paris-sud    (Why GUI)                          */
/*                                                                        */
/*  This software is free software; you can redistribute it and/or        */
/*  modify it under the terms of the GNU Lesser General Public            */
/*  License version 2.1, with the special exception on linking            */
/*  described in file LICENSE.                                            */
/*                                                                        */
/*  This software is distributed in the hope that it will be useful,      */
/*  but WITHOUT ANY WARRANTY; without even the implied warranty of        */
/*  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.                  */
/*                                                                        */
/**************************************************************************/

typedef struct queue { 
  char *contents;
  int length;
  int first, last;
  unsigned int empty, full :1;
} queue;

char t[] = { 0, 0, 0, 0, 0 } ;

queue q = { t, 5, 0, 0, 0, 1};

/*@ invariant q_invariant : 
  @   \valid_range(q.contents, 0, q.length-1) &&
  @   0 <= q.first < q.length &&
  @   0 <= q.last < q.length 
  @   // && (q.full != 0 <=> q.last == q.first)
  @*/

/*@ requires !q.full
  @ assigns  q.empty, q.full, q.last, q.contents[q.last]
  @ ensures  !q.empty && q.contents[\old(q.last)] == c
  @*/
void push(char c) {
  q.contents[q.last++] = c;
  if (q.last == q.length) q.last = 0;
  q.empty = 0;
  q.full = q.first == q.last;
}

/* q.last = (q.last + 1) % q.length; BUG */

/*@ requires !q.empty
  @ assigns q.empty, q.full, q.first
  @ ensures !q.full && \result == q.contents[\old(q.first)]
  @*/
char pop() {
  char r = q.contents[q.first++];
  if (q.first == q.length) q.first = 0;
  q.full = 0;
  q.empty = q.first == q.last;
  return r;
}

/*@ requires \valid(q1) && !q.empty
  @ ensures \result == \old(q1->empty) 
  @*/
int test(struct queue *q1) {
  pop();
  return q1->empty;
}
