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GetNextWorkRequired: clarify why this computation is equivalent to that in the protocol spec. 

refs https://github.com/zcash/zips/pull/418

Signed-off-by: Daira Hopwood <daira@jacaranda.org>
This commit is contained in:
Daira Hopwood 2020-11-12 10:52:49 +00:00
parent 5c47b9bb08
commit 4d16bfd181
1 changed files with 6 additions and 0 deletions
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6
src/pow.cpp
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@ -51,6 +51,12 @@ unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHead
if (pindexFirst == NULL)
return nProofOfWorkLimit;
// The protocol specification leaves MeanTarget(height) as a rational, and takes the floor
// only after dividing by AveragingWindowTimespan in the computation of Threshold(height):
// <https://zips.z.cash/protocol/protocol.pdf#diffadjustment>
//
// Here we take the floor of MeanTarget(height) immediately, but that is equivalent to doing
// so only after a further division, as proven in <https://math.stackexchange.com/a/147832/185422>.
arith_uint256 bnAvg {bnTot / params.nPowAveragingWindow};
return CalculateNextWorkRequired(bnAvg,