200k adjustment start.

libethcore/BlockInfo.cpp

@@ -207,8 +207,9 @@ u256 BlockInfo::calculateDifficulty(BlockInfo const& _parent) const
 	if (!m_number)
 		throw GenesisBlockCannotBeCalculated();
 	u256 o = max<u256>(c_minimumDifficulty, m_timestamp >= _parent.m_timestamp + c_durationLimit ? _parent.m_difficulty - (_parent.m_difficulty / c_difficultyBoundDivisor) : (_parent.m_difficulty + (_parent.m_difficulty / c_difficultyBoundDivisor)));
-	if (unsigned periodCount = unsigned(_parent.number() + 1) / c_expDiffPeriod)
+	unsigned periodCount = unsigned(_parent.number() + 1) / c_expDiffPeriod;
-		o = (u256)max<bigint>(c_minimumDifficulty, bigint(o) - (bigint(1) << (periodCount - 1)));	// latter will eventually become negative, so ensure it's a bigint.
+	if (periodCount > 2)
+		o = (u256)max<bigint>(c_minimumDifficulty, bigint(o) - (bigint(1) << (periodCount - 2)));	// latter will eventually become negative, so ensure it's a bigint.
 	return o;
 }