Re: flag_complex_method = 2 in C++?

[Paolo Carlini <pcarlini at suse dot de>]

Hi Mark,

> I'd prefer not to introduce a situation in which compiling the same code
> with "gcc" and with "g++" behaves differently and which performs worse
> in one case than the other.  Users expect the C subset of C++ to perform
> like C.
>
> If we want the C99 rules, let's just turn them on everywhere, and then
> let users who want "quick and dirty" complex arithmetic to use the flag
> that turns that on.  And, turn that on by default for -ffast-math?
Let's start again from the end of your answer: fast-math includes 
cx_limited_range, which in turn leads to the very fast method *0* being 
used. Therefore, in any case, we cannot have performance issues in 
fast-math mode.

I briefly remind that currently we have *3* different methods, and 
method 1 is the default but for C99, where the default is 2:

/* 0 means straightforward implementation of complex divide acceptable.
  1 means wide ranges of inputs must work for complex divide.
  2 means C99-like requirements for complex multiply and divide.  */

Therefore, I'm not sure... I would certainly like to see method 2 
becoming the default everywhere, on the other hand, I'm not sure if 
method 2 isn't too slow as default for C89 (outside fast-math, I 
repeat). Shall we carry out performance tests perhaps, or peak 
performance outside fast-math aren't really an issue here? I don't know.

In case of doubt, I would still switch to method 2 as default together 
with C++0x, in that case the reference C language is C99 and things are 
very neat...

Paolo.