PHP：将Scientific E值转换为Number

I need to convert following scientific e values to plain string or real number in php

$num1 = 1.2378147769392E+14;

$num2 = 4.9999999999998E-6;

echo number_format($num1, 0, '', ''); // o/p:- 123781477693920

echo number_format($num2, 0, '', ''); // o/p:- 0

The expected output for $num2 is 0.0000049999999999998

enter image description here

The output should come as shown above.

Ref Link: http://www.easysurf.cc/scintd.htm

TIA

$num1 = (int)1.2378147769392E+14;

echo $num1 will return the real number a 123781477693920

$num2 = (int)4.9999999999998E-6;

echo $num2 also will return the real number as 0