47dc4a3180 feat(pow): add difficulty adjustment calculation (Rob N)
Pull request description:
Hi, I hit a roadblock with the current `pow` API. As far as I can tell, the only workaround to calculate the next work required similar to `bitcoin/src/pow.cpp` is to use a general big integer library, convert the `Target` to bytes, do the math, and convert back to `Target` from bytes. I have also been working with [Floresta](780ea8d0b0) and their [solution](780ea8d0b0/crates/floresta-chain/src/pruned_utreexo/consensus.rs (L187)) was to fork off and exposed the `U256` struct publicly on their branch. I think these home brewed difficulty adjustment solutions will continually pop up, so I created a `from_next_work_required` method to return a `Target`. My work veers significantly from #2180, as I only provided a single method to do so, without further guidance on when exactly this retarget occurs.
I am happy to add tests once I get further direction from maintainers if this as a likelihood of being accepted or not. Thanks.
ACKs for top commit:
tcharding:
ACK 47dc4a3180
apoelstra:
ACK 47dc4a3180 used range-diff
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