Documentation request: magic numbers in bitfield.js

[aral]

Is there any documentation on the magic numbers in the bitfield.js (https://github.com/mafintosh/hypercore/blob/master/lib/bitfield.js)?

e.g.,

var INDEX_UPDATE_MASK = [63, 207, 243, 252]
var INDEX_ITERATE_MASK = [0, 192, 240, 252]
var DATA_ITERATE_MASK = [128, 192, 224, 240, 248, 252, 254, 255]
var DATA_UPDATE_MASK = [127, 191, 223, 239, 247, 251, 253, 254]
…
var nibble = [0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4]

I was looking at the Rust implementation and it appears that they are unsure of their meaning/use also: https://github.com/datrs/hypercore/blob/master/src/bitfield/masks.rs

If there’s already some reference/paper/etc. where these are documented, it would help folks trying to understand/port this to have a link to it.

[joehand]

@yoshuawuyts are you covering some of this in https://github.com/datprotocol/book?

[aral]

Ooh, that looks like it’s going to be an invaluable resource; thanks for the link @joehand :)

PS. I think one thing that would help is a good “State of DAT” page that lists the relevant/currently-being-worked on modules/projects (out of the dozens) and documentation and has pathways to discovery for people interesting in using, developing with, and porting DAT. Something short, concise, and frequently updated.

[yoshuawuyts]

@joehand yeah, working on documenting that. It was probably one of the biggest gotchas when implementing hypercore.

It's not quite done yet though. Until then an annotated overview can be found in datrs/hypercore/mask.rs.

[mafintosh]

Closing cause old and lots have changed