std.range.iota enhancement: supporting more types (AKA issue 10762)

[H. S. Teoh]

On Tue, Dec 24, 2013 at 09:27:54AM -0800, H. S. Teoh wrote:
> On Tue, Dec 24, 2013 at 09:10:53AM -0800, Andrei Alexandrescu wrote:
> > On 12/24/13 5:09 AM, Joseph Rushton Wakeling wrote:
> > >On 24/12/13 13:58, monarch_dodra wrote:
> > >>I think you are missing the point of what happens if the step is not
> > >>1 (or if the passed in type can have fractional input). EG:
> > >>
> > >>iota(0, 105, 10);
> > >>or
> > >>iota(0, 10.5);
> > >>
> > >>In this case, "back" should be 100, and not 95. To compute back,
> > >>you need to be able to evaluate length, and to add length*inc to
> > >>front.
> > >
> > >Oh, snap.  Have we been working on the same problems for too long?
> > >:-)
> > 
> > The integral cases are easy. We need to crack the floating point
> > case: given numbers low, up, and step, what's the closest number
> > smaller than up that's reached by repeated adds of step to low?
> [...]
> 
> The closest number is simply step*floor((up-low)/step). There's
> probably a better way to write that expression that avoids bad
> roundoff errors, though.
[...]

Maybe (up - fmod((up-low), step)) might be better? I'm not 100% sure.


T

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