FoVeOOS'11 Competition: challenge 1, in Java
Maximum of an array of integers, in Java
Authors: Claude Marché
Topics: Array Data Structure
References: The COST FoVeOOS'11 Competition
see also the index (by topic, by tool, by reference, by year)
/* COST Verification Competition. vladimir@cost-ic0701.org Challenge 1: Maximum in an array Given: A non-empty integer array a. Verify that the index returned by the method max() given below points to an element maximal in the array. */ /*@ axiomatic integer_max { @ logic integer max(integer x, integer y); @ axiom max_is_ge : \forall integer x y; max(x,y) >= x && max(x,y) >= y; @ axiom max_is_some : \forall integer x y; max(x,y) == x || max(x,y) == y; @ } @*/ public class ArrayMax { /*@ requires a.length > 0; @ ensures 0 <= \result < a.length && @ \forall integer i; 0 <= i < a.length ==> a[i] <= a[\result]; @*/ public static int max(int[] a) { int x = 0; int y = a.length-1; /*@ loop_invariant 0 <= x <= y < a.length && @ \forall integer i; @ 0 <= i < x || y < i < a.length ==> @ a[i] <= max(a[x],a[y]); @ loop_variant y - x; @*/ while (x != y) { if (a[x] <= a[y]) x++; else y--; } return x; } } /* Local Variables: compile-command: "make ArrayMax.why3ml" End: */