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47uint256 private constant MAX_PHASE = 8;
48
49/// `PhaseScheduled` is emitted when the next phase is scheduled.
50event PhaseScheduled(
51    address sender,
52    uint256 newPhase,
53    uint256 scheduledBlock
54);
55
56/// 8 phases each as 32 bits to fit a single 32 byte word.
57uint32[8] public phaseBlocks;

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154function schedulePhase(uint256 phase_, uint256 block_) internal {
155    require(block.number <= block_, "NEXT_BLOCK_PAST");
156    require(block_ < UNINITIALIZED, "NEXT_BLOCK_UNINITIALIZED");
157    // Don't need to check for underflow as the index will be used as a
158    // fixed array index below. Implies that scheduling phase `0` is NOT
159    // supported.
160    uint256 index_;
161    unchecked {
162        index_ = phase_ - 1;
163    }
164    // Bit of a hack to check the current phase against the index to
165    // save calculating the subtraction twice.
166    require(currentPhase() == index_, "NEXT_PHASE");
167
168    require(UNINITIALIZED == phaseBlocks[index_], "NEXT_BLOCK_SET");
169
170    phaseBlocks[index_] = uint32(block_);
171
172    emit PhaseScheduled(msg.sender, phase_, block_);
173}