Function has_implicit_bit

include/fmt/format.h:1527–1530

// Returns true iff Float has the implicit bit which is not stored.
template <typename Float> constexpr auto has_implicit_bit() -> bool {
  // An 80-bit FP number has a 64-bit significand an no implicit bit.
  return std::numeric_limits<Float>::digits != 64;
}

// Returns the number of significand bits stored in Float. The implicit bit is
// not counted since it is not stored.