http://d.puremagic.com/issues/show_bug.cgi?id=9717

           Summary: `std.math.round` rounds away from zero instead of to
                    the nearest even integer
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: major
          Priority: P2
         Component: Phobos
        AssignedTo: nobody@puremagic.com
        ReportedBy: verylonglogin.reg@gmail.com


--- Comment #0 from Denis Shelomovskij <verylonglogin.reg@gmail.com> 2013-03-14 15:16:12 MSK ---
Rounding to the nearest even integer is a default rounding mode and is an expected, useful (e.g. for mesurements rounding), and documented behaviour for `std.math.round`. But instead it currently rounds away from zero (it even uses C's `roundl`).

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hsteoh@quickfur.ath.cx changed:

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--- Comment #1 from hsteoh@quickfur.ath.cx 2013-03-15 10:36:32 PDT ---
Do you have an example code for this bug? I did this:

void main() { writeln(std.math.round(1.4)); }

and the output is 1, as expected.

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monarchdodra@gmail.com changed:

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--- Comment #2 from monarchdodra@gmail.com 2013-03-15 10:46:11 PDT ---
(In reply to comment #1)
> Do you have an example code for this bug? I did this:
> 
> void main() { writeln(std.math.round(1.4)); }
> 
> and the output is 1, as expected.

I believe the "nearest even" is for the .5 tie-breakers:

EG:
round(0.5) == 0
round(1.5) == 2
round(2.5) == 2

It sounds strange at first, but it keeps things "sign agnostic" and nor shifts the average.

http://en.wikipedia.org/wiki/Rounding#Round_half_to_even

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--- Comment #3 from monarchdodra@gmail.com 2013-03-15 10:46:50 PDT ---
That said, "nearest half" is one scheme among many other. I'm not sure about "default".

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--- Comment #4 from Denis Shelomovskij <verylonglogin.reg@gmail.com> 2013-03-16 10:42:37 MSK ---
(In reply to comment #3)
> That said, "nearest half" is one scheme among many other. I'm not sure about "default".

I mean the function is documented to behave this way: http://dlang.org/phobos/std_math.html#round

Also I haven't seen examples where you have to use another theme but I saw ones where you have to use "half to even" theme.

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