manual sqrt function using php

<?php

//for precision number
//number_format(45.234729492, 3) = 45.235;
//number_format(45.234729492, 2) = 45.23;
//number_format(405.234729492, 2) = 405.23;

function mySqrt($number){
    $first_range = 1;
    $last_range = $number;
    $middle_point = 0;
    $sq_middle_point = 0;
    while(true){
        $middle_point = number_format(($first_range+$last_range) / 2, 3);
        $sq_middle_point = number_format($middle_point ** 2, 3);
        if($sq_middle_point == $number){
            break;
        }
        if($sq_middle_point > $number){
            $last_range = $middle_point;
        }else{
            $first_range = $middle_point;
        }

    }
    return $middle_point;
}

echo mySqrt(5);