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/**************************************************************************/
/* */
/* The Why platform for program certification */
/* Copyright (C) 2002-2008 */
/* Romain BARDOU */
/* Jean-Franois COUCHOT */
/* Mehdi DOGGUY */
/* Jean-Christophe FILLITRE */
/* Thierry HUBERT */
/* Claude MARCH */
/* Yannick MOY */
/* Christine PAULIN */
/* Yann RGIS-GIANAS */
/* Nicolas ROUSSET */
/* Xavier URBAIN */
/* */
/* This software is free software; you can redistribute it and/or */
/* modify it under the terms of the GNU General Public */
/* License version 2, as published by the Free Software Foundation. */
/* */
/* 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. */
/* */
/* See the GNU General Public License version 2 for more details */
/* (enclosed in the file GPL). */
/* */
/**************************************************************************/
/*@ lemma mean_property :
@ \forall integer x y; x <= y ==> x <= (x+y)/2 <= y; */
/*@ predicate sorted{L}(long t[]) {
@ \forall integer i j; 0 <= i && i <= j && j < t.length ==>
@ t[i] <= t[j] } */
public class Search {
long t[];
// pb with recursive def of type and logic in Jessie
// @ invariant t_sorted: t != null && sorted(t);
/*@ requires t != null && t.length < 2147483647 && sorted(t);
@ behavior search_success:
@ ensures \result >= 0 ==> t[\result] == v;
@ behavior search_failure:
@ ensures \result < 0 ==>
@ \forall integer k; 0 <= k && k < t.length ==> t[k] != v;
@*/
int binary_search(long v) {
int l = 0, u = t.length-1;
/*@ loop_invariant
@ 0 <= l && u <= t.length-1 &&
@ \forall integer i;
@ 0 <= i && i < t.length ==> t[i] == v ==> l <= i && i <= u;
@ decreases u-l ;
@*/
while (l <= u ) {
int m = (l + u) / 2;
//@ assert l <= m && m <= u;
if (t[m] < v) l = m + 1;
else if (t[m] > v) u = m - 1;
else return m;
}
return -1;
}
}
/*
Local Variables:
compile-command: "make Search"
End:
*/
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