#include <limits.h>
#include "abs.h"
/*@
 requires 0 < n < INT_MAX;
 requires \valid_read(tab+(0..n-1));
 requires \forall integer a,b; 0 <= a < b < n ==> tab[a] - tab[b] <= INT_MAX;
 ensures \forall integer a,b; 0 <= a < b < n ==> \result >= abs(tab[a]-tab[b]);
 */
int max_dist ( int *tab, int n)
{
    int max = tab[0];
    int min = tab[0];
    unsigned int i = 1;
    /*@
        loop assigns i, max, min;
        loop invariant I1: \at(i, LoopEntry) <= i <= n;
        loop invariant I2: min <= max;
        loop invariant I3: \forall integer j; (\at(i, LoopEntry) <= j < i ==> max >= tab[j] >= min);
        loop variant n - i;
    */
     
    while ( i < n)
    {
        if ( tab[i] > max) max = tab[i];
        if ( tab[i] < min) min = tab[i];
        i++;
    }
    //@ assert INT_MIN <= max <= INT_MAX;
    //@ assert INT_MIN <= min <= INT_MAX;
    return max - min;
}