How to do alligned allocation?

[tsbockman]

On Saturday, 1 October 2022 at 00:32:28 UTC, tsbockman wrote:
>             alias Chunk = AliasSeq!(ubyte, ushort, uint, ulong, 
> Chunk16)[shift];

Oops, I forgot that `ulong.alignof` is platform dependent. It's 
probably best to just go ahead and explicitly specify the 
alignment for all `Chunk` types:

```D
private template Aligned(size_t alignment)
     if(1 <= alignment && isPowerOf2(alignment))
{
     enum int shift = bsr(alignment);
     enum size_t mask = alignment - 1;

     static if(alignment <= 16) {
         enum chunkShift = shift, chunkMask = mask;
         align(alignment) struct Chunk {
             void[alignment] data;
         }
     } else {
         enum chunkShift = Aligned!(16).shift, chunkMask = 
Aligned!(16).mask;
         alias Chunk = Aligned!(16).Chunk;
     }
}
```

(This also eliminates the `std.meta : AliasSeq` dependency.)