'use strict';
  
  var toPosInt = require('../../number/to-pos-integer')
    , callable = require('../../object/valid-callable')
    , value    = require('../../object/valid-value')
  
    , floor    = Math.floor;
  
  module.exports = function (compareFn) {
  	var length, low, high, middle;
  
  	value(this);
  	callable(compareFn);
  
  	length = toPosInt(this.length);
  	low = 0;
  	high = length - 1;
  
  	while (low <= high) {
  		middle = floor((low + high) / 2);
  		if (compareFn(this[middle]) < 0) high = middle - 1;
  		else low = middle + 1;
  	}
  
  	if (high < 0) return 0;
  	if (high >= length) return length - 1;
  	return high;
  };