PHPで科学表記法を数値文字列に変換する方法

public function sctonum($num){
    if(false !== stripos($num, "e")){
        $a = explode("e",strtolower($num));
        $b = $a[0] * pow(10,$a[1]);
        return $b;
    }else{
        return $num;
   }
}

public function numToStr($num)
{
	$result = "";
	if (stripos($num, 'e') === false) {
		return $num;
	}
	while ($num > 0) {
		$v = $num - floor($num / 10) * 10;
		$num = floor($num / 10);
		$result = $v . $result;
	}
	return $result;
}

public function sctonum($num, $double = 5){
    if(false !== stripos($num, "e")){
        $a = explode("e",strtolower($num));
        return bcmul($a[0], bcpow(10, $a[1], $double), $double);
    }else{
        return $num;
    }
}
//注$double 是小数位数，可默认设置为没有