[OT] Lower and upper median of 4

[Andrei Alexandrescu via Digitalmars-d]

Thanks! I'll experiment with these and let you know what was best. -- Andrei

On 11/26/2016 05:30 PM, Timon Gehr wrote:
>> 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]);
>> }
>>
>
> Slightly larger code, but uses fewer swaps:
>
> 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]);
>     static if(leanRight){
>         if(r[d]<r[c]){
>             swap(r[c],r[d]);
>             if(r[c]<r[a]) swap(r[a],r[c]);
>         }else if(r[c]<r[b]) swap(r[b],r[c]);
>         assert(r[a]<=r[c]&&r[b]<=r[c]&&r[c]<=r[d]);
>     }else{
>         if(r[b]<r[a]){
>             swap(r[a],r[b]);
>             if(r[d]<r[b]) swap(r[b],r[d]);
>         }else if(r[c]<r[b]) swap(r[b],r[c]);
>         assert(r[a]<=r[b]&&r[b]<=r[c]&&r[b]<=r[d]);
>     }
> }
>
> The best strategy is probably to exhaustively enumerate all
> Pareto-optimal algorithms and to benchmark them automatically within the
> larger algorithm.