Tweaks to difficulty adjustment algorithm
This PR changes the difficulty algorithm to adjust from the average difficulty over the
block window instead of from the last difficulty. It also removes the special rules for the
testnet, which are incompatible with difficulty averaging.
Closes#147 again.
The min-difficulty blocks are incompatible with difficulty averaging.
Network difficulty is also now defined as the difficulty the network is
currently working to solve, rather than the last non-min-difficulty block
difficulty.
"Block difficulty" is the difficulty listed in a block's header, which in the
testnet can sometimes be min-difficulty (if time-since-last-block is too large).
"Network difficulty" is the difficulty that the network was trying to satisfy
at a particular block height. In mainnet this is always equal to the difficulty
of the solved block for that height, but in testnet the network difficulty is
derived from the last non-min-difficulty block difficulty.
This commit fixes the RPC APIs that are intended to show network difficulty, so
that on testnet they don't sometimes drop to 1.0, confusing users.
Closes#1181
The main and test networks are configured to use parameters that are currently
low-memory but usable with the basic solver; they will be increased once the
solver is optimised. The regtest network is configured to have extremely low
memory usage for speed.
Note that Bitcoin's double-hasher is used for the difficulty check. This does
not match the paper, but is simpler than changing the block header
serialization. Single hashing is kept for the EquiHash solver because there is
no requirement on execution time there, only on memory usage.
03c5687 appropriate response when trying to get a block in pruned mode (Jonas Schnelli)
1b2e555 add autoprune information to RPC "getblockchaininfo" (Jonas Schnelli)
