What happened to the profile?

[Linus Torvalds]

On Mon, Oct 7, 2013 at 10:59 AM, Thiago Macieira <thiago at macieira.org> wrote:
>
> There's a private API that avoids memory allocation:
>
> Q_CORE_EXPORT double qstrtod(const char *s00, char const **se, bool *ok);

Looking at the source code for qstrtod(), it looks like it does the
right thing. You can also see how hard it is to actually do it with
proper rounding to the least significant bit. It's about 1700 lines of
code (with comments), much of it accessing the floating point values
directly using integer arithmetic. This comment snippet says a lot:

 * Inspired loosely by William D. Clinger's paper "How to Read Floating
 * Point Numbers Accurately" [Proc. ACM SIGPLAN '90, pp. 92-101].

The Qt code has also clearly been taken from some old BSD source
(looks like NetBSD). It has support for VAX floating point issues etc,
and uses two separate "long" variables each containing up to nine
digits, instead of using an "u64" for up to 18 digits. It has a RCS ID
of 1998, but realistically I suspect the code goes back even further.

So I think the Qt function works, but that thing is declared to be
internal. I think my simple function is perfectly sufficient. I
suspect that in practice, my simple stupid version could be made to be
good to the last bit by simply using "long double" and doing all the
internal calculations in 80-bit FP (on x86). But for our XML parsing
needs, we really don't need it.

                Linus