Three modes of calling i ) With exactly two arguments, the second being an array which's first element is no array. In this case the entire array is searched for the key; -1 is returned if not found, else the index (like member_array(), but faster on sorted arrays).
ii) With two or three arguments, the second being an array which's first element is an array. The array has to have a second element of the same size; the key is searched in the first and the associated element of the second array that is element of second argument is returned if succesful; if not, 0 is returned, or the third argument, if given.
iii) With three or four arguments, the second being an array of keys (first element no array) and the second is a matching data array. Returns 0 or fourth argument (if given) for failure, or the matching entry in the array given as third argument for success.
Complexity : O( lg(n) ) , where n is the number of keys.
Return value is undefined if another list is given in place of a presorted key list.