On 2020-10-26 18:18 -0400, John Cowan wrote:
> On Mon, Oct 26, 2020 at 2:07 PM Wolfgang Corcoran-Mathe <xxxxxx@sigwinch.xyz>
> wrote:
>
> Would it be sufficient to provide C versions of
> > nan-quiet?, nan-negative?, etc., operating on doubles?
> >
>
> That's exactly what I had in mind.  Create a union type in C that can be
> either a double or a uint64, put in the double, get out the uint64, and
> bit-twiddle it, probably 10-15 lines of code.

This would be undefined behavior in C89, but, after a lot of
searching, it does seem that type-punning through unions is valid in
C99 (and C11, allegedly; I don't have a copy of that standard).
Footnote 82 to section 6.5.2.3 (present in more recent drafts of the C99
standard) clarifies this (somewhat):

> If the member used to access the contents of a union object is not
> the same as the member last used to store a value in the object, the
> appropriate part of the object representation of the value is
> reinterpreted as an object representation in the new type as
> described in 6.2.6 (a process sometimes called "type punning").
> This might be a trap representation.

So if a C99 sample implementation would be SRFI-acceptable, I'll
start work on this shortly.

What about make-nan ?  Many reviewers have requested it, and we're
now in a position to provide it.

Regards,

--
Wolfgang Corcoran-Mathe  <xxxxxx@sigwinch.xyz>

"Therefore, 100 victories in 100 battles is not the most skillful.
Subduing the other's military without battle is the most skillful."
--_Sun Tzu_