"%e" floating point format and exponent digits

[Don]

On Wednesday, 20 February 2013 at 22:34:15 UTC, Andrej Mitrovic 
wrote:
> On 2/20/13, David Nadlinger <see at klickverbot.at> wrote:
>> In Phobos, there are quite a few unit tests (std.format,
>> std.json, ...) which assume that the %e floating point format
>> zero-pads the exponent to (at least) two digits.
>
> I don't know about the exponent problem, but w.r.t. floating 
> point
> there was a recent bug fixed where this source file:
>
> auto x = 1.0;
>
> Would be converted to this header file:
>
> auto x = 1;
>
> These are then different types. So I've changed how 
> floating-point is
> written in DMD to always emit "1.0" rather than "1". This also
> improved diagnostics.%
>
> But I wanted to always print at most two digits in this case 
> (e.g.
> 1.00, 2.00, etc) but couldn't find a good way to do it with 
> sprintf,
> so currently for floating-point e.g. "1" it prints "1.00000" in
> diagnostics and header files, which is excessive.
>
> Anyway I would definitely like to see floating-point printing
> synchronized across multiple compilers and also the D library, 
> to be
> consistent everywhere.


Another related issue is the format of %a. On Windows it prints
0x1.444p+99
but on Linux the same number is
0x0.A22p+99
That's much easier to deal with, because it's trivial to print 
the %A format.
Correctly-rounded %e, %f is much more difficult, unfortunately 
(you need some
simple bigint arithmetic).