two questions (issues?) about phobos/std/mmfile.d

[mw]

On Friday, 14 October 2022 at 00:30:55 UTC, mw wrote:
> 2) in ensureMapped() why the requested mmap length are 3x 
> window (2x is enough, since the start offset of the mmap must 
> be multiples of pagesize):
...
> https://github.com/dlang/phobos/blob/master/std/mmfile.d#L582
>
> ```
>                     
> map(window*(iblock-1),cast(size_t)(window*(jblock-iblock+3)));
> // should this be?:
>                     map(window*(iblock),  
> cast(size_t)(window*(jblock-iblock+2)));
>
> ```
>
> So the mapped buffer size is consistent of 2x window?

and in ensureMapped(ulong i, ulong j),

enforce(j - i <= window)?

otherwise, what's the point of allowing user pass in `window` in 
the ctor, if it's not honored?