[OT] Lower and upper median of 4

[Timon Gehr via Digitalmars-d]

On 26.11.2016 22:36, Timon Gehr wrote:
>>>
>>
>> Thanks! Sorry, I forgot to mention partitioning around the lower/upper
>> median is also needed. It seems that changes the tradeoff space. --
>> Andrei
>
> Did you see the suggestion to make the leanLeft/leanRight cases
> symmetric, such that both use at most 4 branches?

Code:

void medianOf(bool leanRight,T)(ref T[4] r, size_t a, size_t b, size_t 
c, size_t d){
     assert(a!=b&&a!=c&&a!=d&&b!=c&&b!=d&&c!=d);
     if(r[c]<r[a]) swap(r[a],r[c]);
     if(r[d]<r[b]) swap(r[b],r[d]);
     if(leanRight?r[d]<r[c]:r[b]<r[a]){
         swap(r[c],r[d]);
         swap(r[a],r[b]);
     }
     if(r[c]<r[b]) swap(r[b],r[c]);
     if(leanRight) assert(r[a]<=r[c]&&r[b]<=r[c]&&r[c]<=r[d]);
     else assert(r[a]<=r[b]&&r[b]<=r[c]&&r[b]<=r[d]);
}