Saturday, July 15, 2017

Best difficulty algorithm: Zawy v1b

# Zawy v1b difficulty algorithm 
# Based on next_diff=average(prev N diff) * TargetInterval / average(prev N solvetimes)
# Thanks to Karbowanec and Sumokoin for supporting, refining, testing, discussing, and using.
# Dinastycoin may be 3rd coin to use it, seeking protection that Cryptonote algo was not providing.
# Original impetus and discussion was at Zcash's modification of Digishield v3. The median method
# Zcash uses should be less accurate and should not be needed for timestamp error protection.
# Wider allowable limit for difficulty per block change provides more protection for small coins.
# Miners should be encouraged to keep accurate timestamps to help negate the effect of attacks.
# Large timestamp limits allows quick return after hash attack. Needed to prevent timestamp manipulation.
# (1+0.693/N) keeps the avg solve time at TargetInterval.
# Low N has better response to short attacks, but wider variation in solvetimes. 
# Sudden large 5x on-off hashrate changes with N=11 sometimes has 30x delays verses 
# 20x delays with N=17. But N=11 may lose only 20 bks in 5 attacks verse 30 w/ N=17.
# For more info: 
# D = difficulty, T = TargetInterval, TS = timestamp, TSL = timestamp limit

N=17;  # can possibly range from N=4 to N>30.  N=17 seems to be a good idea.
TSL=10 if N>10 else TSL = N; # stops miner w/ 50% from lowering  D>25% w/ forward TS's.
current_TS=previous_TS + TSL*T if current_TS > previous_TS + TSL*T;
current_TS=previous_TS - (TSL-1)*T if current_TS < previous_TS - (TSL-1)*T;
next_D = sum(last N Ds) * T / [max(last N TSs) - min(last N TSs] / (1+0.693/N);
next_D = previous_D*1.2 if next_D < 0; 
next_D = 2*previous_D  if next_D/previous_D > 2;
next_D = 0.5*previous_D  if next_D/previous_D < 0.5;

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