The available number of fractional significand bits.
- Xcode 8.0+
- Swift Standard Library
For fixed-width floating-point types, this is the actual number of fractional significand bits.
For extensible floating-point types,
significand should be the maximum allowed significand width (without counting any leading integral bit of the significand). If there is no upper limit, then
significand should be
Float80 is 63, even though 64 bits are used to store the significand in the memory representation of a
Float80 instance. Unlike other floating-point types, the
Float80 type explicitly stores the leading integral significand bit.