Extract an integral payload from a NaN.
the integer payload as a ulong.
For 80-bit or 128-bit reals, the largest possible payload is 0x3FFF_FFFF_FFFF_FFFF. For doubles, it is 0x3_FFFF_FFFF_FFFF. For floats, it is 0x3F_FFFF.
See Implementation
Extract an integral payload from a NaN.