Re: why not consfold sin(const)

[Luchezar Belev <l_belev at yahoo dot com>]

Robert Dewar wrote:

> Luchezar Belev wrote:
> 
> > OK, but in our concrete case we already have some optimizing logic in place
> > which looks if the argument of sin() is zero or if the argument of log() is one,
> > and in the case of sqrt always replaces with const. So if this already present
> > logic is worth enough to be there in the compiler, i fail to see why a full consfolder
> > is not worth enough. It's definitely not the case that it's something too complex
> > for implementing. In fact it's exactly as complex as the currently present logic.
> 
> Not at all, it is far more complex to implement, since you need a very
> accurate set of target independent elementary function routines (you
> can't just go calling these routines from the compiler and using the
> host functions!)
> 
> > Surely the precision is not much of an issue either, since -ffast-math
> > implies possible non-strict copliance with standards, precision requirements, etc.
> 
> Yes, but it does not stretch as far as giving complete junk results,
> which is what would happen in some cases if you used host functions.
 
I see. I'm surprised that in the compiler there is no sin/cos/log/etc. funcs
already implemented for other reasons.

What are the requirements for possible implementation of such functions?
 - precision of somewhere about the long double (64-bit mantissa)
 - the speed doesn't matter too much
is this right?

Lucho


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