What about transforming in two 64 bits numbers.

Than You Frankie for your help.

I would avoid to to reinvent the wheel and write your own math library.

You can use the QD library ported by Timovjl.

I also found another quad precision float library that seems interesting: the

HPALIB (High Precision Arithmetic library).

The IEEE 754 2008 binary128 uses 1 bit for sign, 15bits for exponent and 113bits for mantissa. 113bits means 33 significant digits. This means that you can work i.e. with numbers of 16 digits before decimal dot and 16 digits after without precision loss.