Bit rotation question/challenge

[Afgdr]

On Saturday, 30 January 2021 at 14:40:49 UTC, Afgdr wrote:
> On Saturday, 30 January 2021 at 13:30:49 UTC, burt wrote:
>> I have a static array of `ubyte`s of arbitrary size:
>>
>> ```d
>> ubyte[4] x = [ // in reality, ubyte[64]
>>     0b00001000,
>>     0b00000001,
>>     0b00010101,
>>     0b11110010,
>> ];
>> ```
>>
>> Now I want to bit-rotate the array as if it is one big 
>> integer. So:
>>
>> ```d
>> ubyte[n] rotateRight(size_t n)(ref const ubyte[n] array, uint 
>> rotation)
>> {
>>     // ?
>> }
>> // same for rotateLeft
>>
>> ubyte[4] y = [
>>     0b11111001,
>>     0b00000100,
>>     0b00000000,
>>     0b10001010,
>> ];
>> assert(x.rotateRight(9) == y);
>> assert(y.rotateLeft(9) == x);
>> ```
>>
>> Any ideas how this could be achieved? I.e. what should go at 
>> the "?" for rotateRight and rotateLeft?
>
> cast as uint and shift. cast the result as ubyte[4].

obiously, that works for n=4 with uint and n=8 for ulong, only.