Re: Decimal: Formal review begins

From: Peter Dimov (pdimov_at_[hidden])
Date: 2025-01-21 19:32:20

> The current operator< is this:
> 
> https://godbolt.org/z/Tj7Me5aW3
> 
> This is a sketch of what I was thinking about:
> 
> https://godbolt.org/z/9M1cevYef
> 
> I haven't run this against the test suite, so it might not be quite correct, but it
> looks correct to me. :-)
> 
> It assumes that zeroes are normalized. The current implementation seems to
> not assume that; it handles 0e+7, but since the _fast types are supposed to be
> normalized, this should never happen, should it?

And here's another option, using bitfields:

https://godbolt.org/z/Y7asaMczz

GCC seems to like this better because it's able to figure out that
the exponent and the significand are adjacent in memory, so the
shift+or can be optimized out.

> 
> > This makes me wonder whether { uintNN_t exp_and_mant; bool sign; }
> > wouldn't be a better representation for _fast, although that would
> > depend on how important comparisons are, performance-wise.
> 
> Should look somewhat like this:
> 
> https://godbolt.org/z/bqWKxbdjd
>