Another cool project: make double.to!string CTFEable

[Andrei Alexandrescu via Digitalmars-d]

On 12/16/2015 12:04 PM, tcak wrote:
> On Wednesday, 16 December 2015 at 15:44:45 UTC, Andrei Alexandrescu wrote:
>> This has been discussed in the past and at a point Walter was looking
>> into it.
>>
>> Currently std.conv.to applied to double uses snprintf, which is
>> obviously non-CTFEable.
>>
>> There's been recent work (also discussed here) on fast accurate
>> printing of floating point values, see library "double-conversion"
>> written in C++ and the associated paper
>> http://www.cs.tufts.edu/~nr/cs257/archive/florian-loitsch/printf.pdf.
>>
>> Implementing that in D would be awesome because there are many many
>> applications of CTFEing doubles converted to text.
>>
>>
>> Andrei
>
> If the purpose is to make it CTFEable, then we need to make it work at
> first. So, there
> is no need to focus on fast accurate implementation.

This strategy may be a bit risky because then we have slightly different 
numbers at compile vs. run time etc.

> I will try to
> implement it by
> multiplication and modulus operations at compile time. But I am not sure
> about how long the decimal part (I don't know what the part after point
> is called) should be. Would it be acceptable if it becomes 100 digits in
> string? What is the limit?

Probably mimicking what to does right now would be a good baseline.


Andrei