Support calculation in Excel's double precision

Excel handle double in different way.
1. Input number would be cut to only 15 significant digits (while IEEE754 used in double can represent 17 digits)
2. temporary number calculation result in formula is rounded(not cut) into 15 precision.

The following calculation will results in 5.820766091346741E-11 in IEEE754 calculation but it is expected to be zero.

=-732870.32 - -207279.38 - -4737.63 - -4737.89 - -516115.42