Re: [PATCH] [ranger] x == -0.0 does not mean we can replace x with -0.0

[Jeff Law <jeffreyalaw@gmail.com>]

On 8/29/2022 9:13 AM, Toon Moene wrote:
> On 8/29/22 17:08, Jeff Law via Gcc-patches wrote:
>
>>> However, I'm hoping to forget as many floating point details, as fast
>>> as possible, as soon as I can ;-).
>
>> Actually FP isn't that bad -- I'd largely avoided it for decades, but 
>> didn't have a choice earlier this year.  And there's a lot more 
>> headroom for improvements in the FP space than the integer space IMHO.
>
> One of the more interesting ones is to try to limit the range of the 
> input to the trigonometric functions - that way you could use ones 
> without any argument reduction phase ...
The difficult part is that most of the trig stuff is in libraries, so we 
don't have visibility into the full range.

What we do sometimes have is knowledge that the special values are 
already handled which allows us to do things like automatically 
transform a division into estimation + NR correction steps (atan2).

I guess we could do specialization based on the input range.  So rather 
than calling "sin" we could call a special one that didn't have the 
reduction step when we know the input value is in a sensible range.

Jeff