Calculates high order bit mask for a word size

highOrderBitmask.php

<? php
function high_order_bitmask($wordSize) {
  if($wordSize == 0 or $wordSize == 1){
    return 0;
  }
  $bitmask = 0;
  for($i=$wordSize-1; $i >= $wordSize/2; $i-- ){
    $bitmask += pow(2,$i);
  }
  return $bitmask;
}
class HighOrderBitmaskSolution extends TestCase
{
    public function testTwoBits() {
      $this->assertSame(2, high_order_bitmask(2));
    }
    public function testFourBits() {
      $this->assertSame(12, high_order_bitmask(4));
    }
    public function testEightBits() {
      $this->assertSame(240, high_order_bitmask(8));
    }
}