>> It'd probably have to be touched up a bit.

> This may be an understatement. :-)

Probably so.  Nevertheless, it's got to be easier
than approaching the problem from scratch.
And considering that this discussion has been
going on for over a year now, it might be a way to
move forward.

> In the first 50 lines of the 3897-line dtoa.c file, I see this warning:
>
> /* On a machine with IEEE extended-precision registers, it is
>  * necessary to specify double-precision (53-bit) rounding precision
>  * before invoking strtod or dtoa.  [...] */
>
> It seems to me that figuring out how and when to do this, and
> writing and testing the appropriate configure/pyport/whatever
> code, is already a nontrivial task.

I would consider compiling the library with flags appropriate to forcing
64-bit IEEE arithmetic if possible.  Another possibility is to explore
gdtoa.c
which is supposed to include code for extended precision, quad precision,
etc.