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/**************************************************************************/
/* */
/* The Why platform for program certification */
/* */
/* Copyright (C) 2002-2011 */
/* */
/* Jean-Christophe FILLIATRE, CNRS & Univ. Paris-sud 11 */
/* Claude MARCHE, INRIA & Univ. Paris-sud 11 */
/* Yannick MOY, Univ. Paris-sud 11 */
/* Romain BARDOU, Univ. Paris-sud 11 */
/* */
/* Secondary contributors: */
/* */
/* Thierry HUBERT, Univ. Paris-sud 11 (former Caduceus front-end) */
/* Nicolas ROUSSET, Univ. Paris-sud 11 (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 11 (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. */
/* */
/**************************************************************************/
// RUNSIMPLIFY this tells regtests to run Simplify in this example
//@ lemma mean: \forall integer x, y; x <= y ==> x <= (x+y)/2 <= y;
/*@ predicate sorted{L}(long *t, integer a, integer b) =
@ \forall integer i,j; a <= i <= j <= b ==> t[i] <= t[j];
@*/
/*@ requires n >= 0 && \valid_range(t,0,n-1);
@ ensures -1 <= \result < n;
@ behavior success:
@ ensures \result >= 0 ==> t[\result] == v;
@ behavior failure:
@ assumes sorted(t,0,n-1);
@ ensures \result == -1 ==>
@ \forall integer k; 0 <= k < n ==> t[k] != v;
@*/
int binary_search(long t[], int n, long v) {
int l = 0, u = n-1;
/*@ loop invariant
@ 0 <= l && u <= n-1;
@ for failure:
@ loop invariant
@ \forall integer k; 0 <= k < n && t[k] == v ==> l <= k <= u;
@ loop variant u-l;
@*/
while (l <= u ) {
int m = (l + u) / 2;
//@ assert l <= 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 binary_search.why3ml"
End:
*/
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