Proposal: fixing the 'pure' floating point problem.

[Michel Fortin]

On 2009-03-16 08:27:28 -0400, Don <nospam at nospam.com> said:

> That requires a new keyord, four new calling conventions, a new name 
> mangling scheme, compiler insertion of special code, nasty issues with 
> function pointers, ...

Which isn't much different as adding a new extern(x) option, for which 
all these problems have been solved.


> for a feature that almost nobody will ever use. And it doesn't deal 
> with    dynamic rounding mode.

Well, isn't it dynamic rounding mode? I ask because you can change the 
mode dynamically by calling a function. With floatmode(neutral) you 
tell which function support any rounding mode, and with floatmode(x) 
you choose which rounding mode to use within a function. It just makes 
sure those changes are scoped and limit them to function boundaries.

If you want to evaluate the same function with two rounding modes, just 
create a template:

	R roundUp(alias a, R)(float arg) floatmode(round_up)
	{
		return a(arg);
	}
	R roundDown(alias a, R)(float arg) floatmode(round_down)
	{
		return a(arg);
	}

then call it:

	roundUp!(sin)(8);
	roundDown!(sin)(8);


> And it doesn't solve the problem of the sticky flags.

As for sticky flags, couldn't they be returned by the template when you 
care about them? Something like:

	struct FloatAndStickyFlags {
		this(float, int);
		float value;
		int sticky_flags;
	}
	FloatAndStickyFlags roundDownGetStickyFlags(alias a, R)(float arg) 
floatmode(round_down)
	{
		return FloatAndStickyFlags(a(arg), getStickyFlags());
	}


-- 
Michel Fortin
michel.fortin at michelf.com
http://michelf.com/