Floating point rounding

[ag0aep6g via Digitalmars-d-learn]

On 03/02/2017 10:10 PM, Guillaume Chatelet wrote:
> On Thursday, 2 March 2017 at 20:30:47 UTC, Guillaume Chatelet wrote:
>> Here is the same code in D:
>> void main(string[] args)
>> {
>>     import std.math;
>>     FloatingPointControl fpctrl;
>>     fpctrl.rounding = FloatingPointControl.roundUp;
>>     writefln("%.32g", float.min_normal + 1.0f);
>> }
>>
>> Execution on my machine yields:
>> dmd -run test_denormal.d
>> 1
>>
>> Did I miss something?
>
> This example is closer to the C++ one:
>
> void main(string[] args)
> {
>     import core.stdc.fenv;
>     fesetround(FE_UPWARD);
>     writefln("%.32g", float.min_normal + 1.0f);
> }
>
> It still yields "1"

This prints the same as the C++ version:

----
void main(string[] args)
{
     import std.stdio;
     import core.stdc.fenv;
     fesetround(FE_UPWARD);
     float x = 1.0f;
     x += float.min_normal;
     writefln("%.32g", x);
}
----

Soo, a bug/limitation of constant folding?

With FloatingPointControl it still prints "1". Does 
FloatingPointControl.rounding do something different than fesetround? 
The example in the docs [1] only shows how it changes rint's behavior.


[1] http://dlang.org/phobos/std_math.html#.FloatingPointControl