Re: Performance improvements for src/port/snprintf.c

Andres Freund <andres@anarazel.de> writes:
> It seems the general "use strfromd if available" approach is generally
> useful, even if we need to serialize the precision.

Agreed.

> Putting it into an
> inline appears to be helpful, avoids some of the otherwise precision
> related branches.  Do you have any feelings about which header to put
> the code in?  I used common/string.h so far.

I do not think it should be in a header, for two reasons:

(1) The need to use sprintf for portability means that we need very
tight constraints on the precision spec *and* the buffer size *and*
the format type (%f pretty much destroys certainty about how long the
output string is).  So this isn't going to be general purpose code.
I think just writing it into float[48]out is sufficient.

(2) It's already the case that most code trying to emit floats ought
to go through float[48]out, in order to have standardized treatment
of Inf and NaN.  Providing some other API in a common header would
just create a temptation to break that policy.

Now, if we did write our own float output code then we would standardize
Inf/NaN outputs inside that, and both of these issues would go away ...
but I think what we'd do is provide something strfromd-like as an
alternate API for that code, so we still won't need a wrapper.
And anyway it doesn't sound like either of us care to jump that hurdle
right now.

			regards, tom lane