Address ChainSecurity questions #90
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They should never be encountered in normal operation. Addresses ChainSecurity audit 7.1 & 7.5.
Addresses ChainSecurity audit 7.6.
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| // should not revert under any input | ||
| function test_averageAge(uint120 _currentTimestamp, uint120 _timestamp) public { |
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Removing useless test.
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| // should not revert under any input | ||
| function test_calculateAverageTimestamp( |
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Removing harmful test. It should very much revert when passed nonsensical arguments.
The average timestamp is a weighted average of the form:
t_avg = SUM_i(t_i * lqty_i) / SUM_i(lqty_i)
It is always legal to add any number of new (t_j, lqty_j) pairs to an existing weighted average, in which case the new average will be:
t_avg' = (t_avg * SUM_i(lqty_i) + SUM(t_j * lqty_j)) / (SUM_i(lqty_i) + SUM_j(lqty_j))
= (t_avg * SUM_i(lqty_i) + [SUM(t_j * lqty_j) / SUM_j(lqty_j)] * SUM_j(lqty_j)) / (SUM_i(lqty_i) + SUM_j(lqty_j))
Note: the parameters of the function
_calculateAverageTimestamp()correspond to the following terms:
_prevOuterAverageTimestamp=>t_avg_newInnerAverageTimestamp=>SUM(t_j * lqty_j) / SUM_j(lqty_j)_prevLQTYBalance=>SUM_i(lqty_i)_newLQTYBalance=>SUM_i(lqty_i) + SUM_j(lqty_j)This explains the seemingly overcomplicated second form of
t_avg'above.
However, when removing previously allocated amounts, even if we allow partial deallocation, the parameter _newInnerAverageTimestamp itself must be a valid weighted average of the form:
_newInnerAverageTimestamp = SUM_i(t_i * lqtyDecrease_i) / SUM_i(lqtyDecrease_i)
where forall i. lqtyDecrease_i <= lqty_i. Failing to adhere to this constraint can and should result in reverts.
| return uint120( | ||
| _newInnerAverageTimestamp + _prevOuterAverageTimestamp * _prevLQTYBalance / _newLQTYBalance | ||
| - _newInnerAverageTimestamp * _prevLQTYBalance / _newLQTYBalance | ||
| ); |
Eliminate unnecessary corner cases & special checks that should never be encountered/needed in normal operation.
Fix code comment about states in which user can vote positively.
Addresses ChainSecurity audit 7.1, 7.5 & 7.6.
Closes IR-09 & IR-10.