[un]signed double float

A double float is a standard IEEE 754 floating point value of 64 bits.

The value is defined as follow:

• 1 bit for the sign
• 11 bits for the exponent
• 52 bits for the mantissa

This type is similar to most processor double float type and can thus be used directly.

Note that in some cases, double floats are saved with the lower 32 bits of their mantissa after the upper bits. In other wise, the two 32 bits value are swapped.