Add bitwise operations to BigNumber

[SilentCicero]

Hey Richard,

Does ethers expose the plain BN object anywhere, there were some BN specific methods I need and it seems your wrapper doesn't include them (i think it was shifting).

Regardless, might be good to just expose the plain BN object for these pinch cases.

Best,
Nick

[ricmoo]

No, it’s not exposed. If you npm the same version in your project, it should reuse the same copy during rollup though.

The reason to not expose it is that some day I plan to remove it, and if people depend on it from ethers, than I can’t remove it without breaking them. It is very much meant to be internal. :)

What functionality do you need? There shouldn’t be any methods normal ethereum development should need beyond was is exposed, I think?

[SilentCicero]

Very understandable, what's the long term BN strategy?

I think it was missing some Bit operations that I needed, shift right/left/pow etc:

Bit operations

a.shln(b) - shift left (i, u, iu)
a.shrn(b) - shift right (i, u, iu)

Would be nice to just use ethers here, and it's just a few methods I couldn't seem to find in ethers. Maybe I just didn't see them?

[SilentCicero]

I think something like this should do it #782

[ricmoo]

The pow function is present, but bitshifts are not. Other than maskn (which is required for the ABI coder), I’ve avoided bitwise operations, because they aren’t usually required, and for arbitrary precision some operations are not well-defined and many implementations try to “find a way” (the prime example being bitwise not).

That said, I can imaging people using a uint256 as a bit field (I have), so and, or, shl, shr and sar probably make sense to add. There won’t be a not though and I’ll add notes to the docs as to why the other bitwise operations were added but not that one...

It prolly won’t happen right away though. Still trying to get the new docs ready first so I can finally release v5. :)

[SilentCicero]

Nice! I think a hefty explainer on the concerns of Bit Wise implementation concerns would be a nice addition to the docs.

Secondly, what are you using for the docs? Same tech, or a new platform?

[SilentCicero]

One last thing...

I really, really hate looking at and typing bigNumberify every time.

Why not just big, please one day consider big. It can be our secret.

[ricmoo]

In v5, it’s BigNumber.from. Moving (slowly) away from magic functions. :)

For the most part though, you shouldn’t need to explicitly convert numbers to BigNumber, since most functions do that for you.

The new docs are written in Flatworm, because as much as I advocate against re-inventing the wheel, I often fail to heed my own advice. I’m almost done refactoring it, so it will be easier to add full-text search and PDF output. :)

[SilentCicero]

@ricmoo I might use flatworm also, looks good, my own problem is it has too many dependancies.

Why don't you trim it down a bit ;)

[ricmoo]

Tests are running right now.

I've restricted all operations to positive numbers.

The and, or and xor operations are complicated (or not well defined) for negative values of arbitrary bit width.

The shift operations shl and shr require a positive shift offset (technically a negative offset could referent to an offset of the opposite direction, but for now I'm making the decision to not allow this).

I also omitted arithmetic right shift, since it is not common and I need to think more about what it means in the context of arbitrary bit width.

The mod also only allows a positive modulo.

Hopefully these all make sense and help. :)

[ricmoo]

Published to 5.0.0-beta.181.

Try it out and let me know if you have any problems.

[SilentCicero]

Thanks Richard!

…

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On Apr 15, 2020, at 7:21 PM, Richard Moore ***@***.***> wrote: Published to 5.0.0-beta.181. Try it out and let me know if you have any problems. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub, or unsubscribe.

[ricmoo]

Coolio. Closing this now.

Thanks! :)

[samlaf]

I don't see shl or any other of the bit operations documented in the docs (https://docs.ethers.io/v5/api/utils/bignumber/#BigNumber). Would be nice/essential to have.

[ricmoo]

Agreed. I’ll add them on the next docs pass.

[barakman]

So what's the status on this? Still no bit-wise operations in the doc.

[Mouradif]

Still no bitwise operations in the doc (for people who still want to use v5)