$num1 = "10.5";
$num2 = "2.5";
$result = bcmul($num1, $num2, 2); // 结果为 26.25
$num1 = "10.5";
$num2 = "2.5";
$result = bcmul($num1, $num2, 0); // 结果为 26
$num1 = "999999999999999999999999999";
$num2 = "999999999999999999999999999";
$result = bcmul($num1, $num2); // 结果为 999999999999999999999999998000000000000000000000000001
$num1 = "1.23456789e5";
$num2 = "2.3456789e4";
$result = bcmul($num1, $num2); // 结果为 2895708.9564221