Proposal: fixing the 'pure' floating point problem.

[Philip Miess]

Walter Bright wrote:
> Don wrote:
>> That's true, but if you're in a floatingpoint module, and you call a 
>> non-floatingpoint module, it's your responsibility to make sure that 
>> the rounding mode is back to normal. You're saying that you don't care 
>> about the status flags. So it's your own fault if you get surprising 
>> results.
>>
>> The primary use for adjusting the rounding mode is for things like 
>> implementing interval arithmetic. Thus, it's only ever used for small 
>> functions.
> 
> Perhaps we can go with something simpler. If you call a pure function, 
> then the modes must be set to their defaults.


Walter,
	I had a simpler idea.
What about a default rounding mode parameter on pure functions that care 
about the rounding mode.

like this

pure int sqrt(int x, invariant roundingMode round = default)
{
	return x*x;
}

No change to D is necessary to use this.
If you wanted to make it a little easier you could
provide a standard rounding mode class that gets the current rounding mode.
now if don't want to use the default rounding mode you pass the rounding 
Mode your using as a parameter.
The function can be cached since it's output only depends on its input.

In summary, if your pure function depends on the rounding mode that 
should be a parameter of your function.
What do you think, will that work?

Phil