newCTFE Status November 2018

[Joakim]

On Sunday, 9 December 2018 at 16:32:49 UTC, Nathan S. wrote:
> On Saturday, 8 December 2018 at 15:56:46 UTC, kinke wrote:
>> [...]
>
> This infallibly determines the precision used for calculations 
> involving `real` in CTFE:
>
> ----
> enum ctfeRealExponentBits =
> () {
>     real f = 2;
>     foreach (i; 1 .. 2000)
>     {
>         real g = f * f;
>         if (g == f)
>             return i;
>         f = g;
>     }
>     assert(0, "algorithm failure");
> }();
>
> enum ctfeMantissaBits =
> () {
>     real a = 1;
>     real b = 0.5;
>     int bits = 0;
>     while (a + b != a)
>     {
>         bits = bits + 1;
>         b = b / 2;
>     }
>     // Result matches what would be reported by mant_dig
>     // (1 greater than the actual number of mantissa bits
>     // except for 80-bit extended precision).
>     return bits + 1;
> }();
> ----

Heh, yes, checking the precision manually with a compile-time 
while loop works: he meant there's no "FP type properties" that 
will easily give it to you.