_validPrice can include floor and ceiling values when checking the validity

[cleanunicorn]

Description

A price is considered valid if the internal method _validPrice returns true.

review-volt-core-2022-09/code/contracts/peg/PriceBoundPSM.sol

Lines 122 to 135 in 5826c86

	/// @notice helper function to determine if price is within a valid range
	function _validPrice(Decimal.D256 memory price)
	internal
	view
	returns (bool valid)
	{
	valid =
	price.greaterThan(
	Decimal.ratio(floor, Constants.BASIS_POINTS_GRANULARITY)
	) &&
	price.lessThan(
	Decimal.ratio(ceiling, Constants.BASIS_POINTS_GRANULARITY)
	);
	}

This method checks if the provided price is strictly greater than the floor and strictly less than the floor.

review-volt-core-2022-09/code/contracts/peg/PriceBoundPSM.sol

Lines 129 to 134 in 5826c86

	price.greaterThan(
	Decimal.ratio(floor, Constants.BASIS_POINTS_GRANULARITY)
	) &&
	price.lessThan(
	Decimal.ratio(ceiling, Constants.BASIS_POINTS_GRANULARITY)
	);

These methods are taken from the Decimal library.

review-volt-core-2022-09/code/contracts/external/Decimal.sol

Lines 163 to 177 in 5826c86

	function greaterThan(D256 memory self, D256 memory b)
	internal
	pure
	returns (bool)
	{
	return compareTo(self, b) == 2;
	}
	function lessThan(D256 memory self, D256 memory b)
	internal
	pure
	returns (bool)
	{
	return compareTo(self, b) == 0;
	}

Using a strictly greater/less check will exclude the values of floor and ceiling as being valid. This forces the governance to add floor and ceiling values similar to floor = 0.7999999999999 and ceiling = 1.199999999999 to describe a valid interval from 0.8 to 1.2, included.

If the check would accept the limits as valid, the governance could set floor = 0.8 and ceiling = 1.2, which are a lot easier to reason about and verify.

Recommendation

Consider using the methods greaterThanOrEqualTo and lessThanOrEqualTo provided by Decimal to avoid using awkward values.

review-volt-core-2022-09/code/contracts/external/Decimal.sol

Lines 179 to 193 in 5826c86

	function greaterThanOrEqualTo(D256 memory self, D256 memory b)
	internal
	pure
	returns (bool)
	{
	return compareTo(self, b) > 0;
	}
	function lessThanOrEqualTo(D256 memory self, D256 memory b)
	internal
	pure
	returns (bool)
	{
	return compareTo(self, b) < 2;
	}

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