Check that on difficulty adjustments, the new difficulty does not increase or decrease beyond the permitted limits.
| 87 | // Check that on difficulty adjustments, the new difficulty does not increase |
| 88 | // or decrease beyond the permitted limits. |
| 89 | bool PermittedDifficultyTransition(const Consensus::Params& params, int64_t height, uint32_t old_nbits, uint32_t new_nbits) |
| 90 | { |
| 91 | if (params.fPowAllowMinDifficultyBlocks) return true; |
| 92 | |
| 93 | if (height % params.DifficultyAdjustmentInterval() == 0) { |
| 94 | int64_t smallest_timespan = params.nPowTargetTimespan/4; |
| 95 | int64_t largest_timespan = params.nPowTargetTimespan*4; |
| 96 | |
| 97 | const arith_uint256 pow_limit = UintToArith256(params.powLimit); |
| 98 | arith_uint256 observed_new_target; |
| 99 | observed_new_target.SetCompact(new_nbits); |
| 100 | |
| 101 | // Calculate the largest difficulty value possible: |
| 102 | arith_uint256 largest_difficulty_target; |
| 103 | largest_difficulty_target.SetCompact(old_nbits); |
| 104 | largest_difficulty_target *= largest_timespan; |
| 105 | largest_difficulty_target /= params.nPowTargetTimespan; |
| 106 | |
| 107 | if (largest_difficulty_target > pow_limit) { |
| 108 | largest_difficulty_target = pow_limit; |
| 109 | } |
| 110 | |
| 111 | // Round and then compare this new calculated value to what is |
| 112 | // observed. |
| 113 | arith_uint256 maximum_new_target; |
| 114 | maximum_new_target.SetCompact(largest_difficulty_target.GetCompact()); |
| 115 | if (maximum_new_target < observed_new_target) return false; |
| 116 | |
| 117 | // Calculate the smallest difficulty value possible: |
| 118 | arith_uint256 smallest_difficulty_target; |
| 119 | smallest_difficulty_target.SetCompact(old_nbits); |
| 120 | smallest_difficulty_target *= smallest_timespan; |
| 121 | smallest_difficulty_target /= params.nPowTargetTimespan; |
| 122 | |
| 123 | if (smallest_difficulty_target > pow_limit) { |
| 124 | smallest_difficulty_target = pow_limit; |
| 125 | } |
| 126 | |
| 127 | // Round and then compare this new calculated value to what is |
| 128 | // observed. |
| 129 | arith_uint256 minimum_new_target; |
| 130 | minimum_new_target.SetCompact(smallest_difficulty_target.GetCompact()); |
| 131 | if (minimum_new_target > observed_new_target) return false; |
| 132 | } else if (old_nbits != new_nbits) { |
| 133 | return false; |
| 134 | } |
| 135 | return true; |
| 136 | } |
| 137 | |
| 138 | // Bypasses the actual proof of work check during fuzz testing with a simplified validation checking whether |
| 139 | // the most significant bit of the last byte of the hash is set. |