This patch does two things:
1) The branches for `sizeof(_Dp) == sizeof(int32_t)` and `sizeof(_Dp) ==
sizeof(int64_t)` are merged, since these are basically identical.
2) The branch where `numeric_limits<_Dp>::radix != 2` is removed, since
no platform we support (nor any I'm aware of) have a floating point type
with `radix != 2`. This means that the branch is basically dead code.
5f0f7580aa