Speed up Store instances for (Byte)Strings of known size

[sjakobi]

Stack.Types.BuildPlan.GitSHA1 currently derives its Store instance from the underlying ByteString, so store must assume a variable size. A handwritten instance could use the fact that a SHA1 digest has 20 bytes and would probably be a bit faster, and – depending on architecture – 4 or 8 bytes shorter.

The same could be done for Stack.Types.PackageIndex.PackageDownload.pdSHA256 and probably other types.

If there isn't already a set of helpers for ByteStrings of known size in store, maybe it should be added! :)

[sjakobi]

If there isn't already a set of helpers for ByteStrings of known size in store, maybe it should be added! :)

See StaticSize.

[mgsloan]

Yep, I think StaticSize is our answer to this, closing

[sjakobi]

Reopening, as stack's Store instances still need to make use of StaticSize, right?!

[mgsloan]

Oh, true! I thought this was on the store tracker.

[alexeyzab]

Hi there!

I'd like to try implementing this. I'll be sending a PR shortly, let me know if I am on the right track. Thanks!

[alexeyzab]

I believe this can be closed.

[snoyberg]

Sounds good, thanks for catching that!