Wrote a blog post about CTFE and D

[Danny Arends]

On Saturday, 1 September 2012 at 01:46:38 UTC, Rene Zwanenburg 
wrote:
> On Thursday, 30 August 2012 at 09:41:43 UTC, Danny Arends wrote:
>> I wrote a blog post about the stuff I've been doing last 
>> weekend using CTFE.
>> All comments are welcome, you can find the blog post at:
>>
>> http://www.dannyarends.nl/index.cgi?viewDetailed=00029
>>
>> Danny Arends
>> http://www.dannyarends.nl
>
> It's always good to see someone write about the unusual 
> features of D, but I have a non-D related point of criticism 
> regarding your post: lookup tables for trig functions are a 
> thing from the nineties.

Thanks for reply! I see you got the point from the post :)

The stuff I implemented in CTFE is course many times worse then 
the std.math sine and cosine functions (they fall back to single 
operators in ASM)I could have just as well done:

pure T[2][] gen_trigonometric(){
   T[2][] result = new T[2][](360);
   foreach(i; 0 .. 360){
     result[i] = [sin(x), cos(x)];
   }
   return result;
}

But well then showing off D's feature to call (polymorphic) user 
functions in CTFE is then less clear :)

>
> I'm not trying to make some bad 'the nineties called' joke ;). 
> Since at least a decade, calling the trig functions will 
> usually be significantly faster in a real application than a 
> lookup table. Simple benchmarks may show a performance 
> improvement, but that's because the table still resides in the 
> L1 cache. A real application will often have to read the table 
> from main memory, which is orders of magnitude slower than 
> simply doing the computation.
>
> Use caching for data which is really expensive to calculate. 
> For relatively trivial stuff like sin(), just calculate it 
> during runtime.

I don't try to advocating people start using look-up tables for 
sine and cosine. It's an example to show how cool I think CTFE is 
for stuff like this. I could have also taken the much more used 
example of CTFE calculating primes. However in that case (primes) 
it is not useful to have a user function doing it for
floats, doubles and reals. :-P

Gr,
Danny Arends