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馃ア Correct rounding direction comments in FixedPointMathLib.sol #1558

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Merged
atarpara merged 1 commit into from
Sep 1, 2026
Merged

馃ア Correct rounding direction comments in FixedPointMathLib.sol #1558

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8 changes: 4 additions & 4 deletions src/utils/FixedPointMathLib.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -75,7 +75,7 @@ library FixedPointMathLib {
}
}

/// @dev Equivalent to `(x * y) / WAD` rounded down.
/// @dev Equivalent to `(x * y) / WAD` rounded towards zero.
function sMulWad(int256 x, int256 y) internal pure returns (int256 z) {
/// @solidity memory-safe-assembly
assembly {
Expand All @@ -97,7 +97,7 @@ library FixedPointMathLib {
}
}

/// @dev Equivalent to `(x * y) / WAD` rounded down, but without overflow checks.
/// @dev Equivalent to `(x * y) / WAD` rounded towards zero, but without overflow checks.
function rawSMulWad(int256 x, int256 y) internal pure returns (int256 z) {
/// @solidity memory-safe-assembly
assembly {
Expand Down Expand Up @@ -142,7 +142,7 @@ library FixedPointMathLib {
}
}

/// @dev Equivalent to `(x * WAD) / y` rounded down.
/// @dev Equivalent to `(x * WAD) / y` rounded towards zero.
function sDivWad(int256 x, int256 y) internal pure returns (int256 z) {
/// @solidity memory-safe-assembly
assembly {
Expand All @@ -164,7 +164,7 @@ library FixedPointMathLib {
}
}

/// @dev Equivalent to `(x * WAD) / y` rounded down, but without overflow and divide by zero checks.
/// @dev Equivalent to `(x * WAD) / y` rounded towards zero, but without overflow and divide by zero checks.
function rawSDivWad(int256 x, int256 y) internal pure returns (int256 z) {
/// @solidity memory-safe-assembly
assembly {
Expand Down
62 changes: 62 additions & 0 deletions test/FixedPointMathLib.t.sol
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Expand Up @@ -674,6 +674,68 @@ contract FixedPointMathLibTest is SoladyTest {
assertEq(FixedPointMathLib.sDivWad(0, 1e18), 0);
}

function testSMulWadRoundsTowardsZero() public {
assertEq(FixedPointMathLib.sMulWad(-1, 1), 0);
assertEq(FixedPointMathLib.sMulWad(1, -1), 0);
assertEq(FixedPointMathLib.sMulWad(-1, 3), 0);
assertEq(FixedPointMathLib.sMulWad(-0.5e18, 1), 0);
// Exact quotient is -3.000000000000000003.
assertEq(FixedPointMathLib.sMulWad(-1000000000000000001, 3), -3);
assertEq(FixedPointMathLib.sMulWad(1000000000000000001, -3), -3);
assertEq(FixedPointMathLib.sMulWad(-1, -1), 0);
assertEq(FixedPointMathLib.sMulWad(1000000000000000001, 3), 3);
}

function testSDivWadRoundsTowardsZero() public {
assertEq(FixedPointMathLib.sDivWad(-1, 3), -333333333333333333);
assertEq(FixedPointMathLib.sDivWad(1, -3), -333333333333333333);
assertEq(FixedPointMathLib.sDivWad(-1e18, 3), -333333333333333333333333333333333333);
assertEq(FixedPointMathLib.sDivWad(1e18, -3), -333333333333333333333333333333333333);
assertEq(FixedPointMathLib.sDivWad(-1, -3), 333333333333333333);
assertEq(FixedPointMathLib.sDivWad(1, 3), 333333333333333333);
}

function testRawSMulWadEdgeCases() public {
assertEq(FixedPointMathLib.rawSMulWad(-1, 1), 0);
assertEq(FixedPointMathLib.rawSMulWad(-1000000000000000001, 3), -3);
assertEq(FixedPointMathLib.rawSMulWad(type(int256).max, 2), 0);
vm.expectRevert(FixedPointMathLib.SMulWadFailed.selector);
this.sMulWad(type(int256).max, 2);
}

function testRawSDivWadEdgeCases() public {
assertEq(FixedPointMathLib.rawSDivWad(-1, 3), -333333333333333333);
assertEq(FixedPointMathLib.rawSDivWad(1e18, 0), 0);
vm.expectRevert(FixedPointMathLib.SDivWadFailed.selector);
this.sDivWad(1e18, 0);
assertEq(FixedPointMathLib.rawSDivWad(type(int256).max, 1), -1e18);
vm.expectRevert(FixedPointMathLib.SDivWadFailed.selector);
this.sDivWad(type(int256).max, 1);
}

function testSMulWadRoundsTowardsZero(uint256 xSeed, uint256 ySeed) public {
int256 x = int256(_bound(xSeed, 0, 2e24)) - 1e24;
int256 y = int256(_bound(ySeed, 0, 2e24)) - 1e24;
int256 z = FixedPointMathLib.sMulWad(x, y);
assertEq(z, (x * y) / 1e18); // Solidity's `/` on `int256` truncates towards zero.
assertEq(FixedPointMathLib.rawSMulWad(x, y), z);
assertEq(FixedPointMathLib.sMulWad(-x, y), -z); // Flooring would not be sign symmetric.
assertLe(FixedPointMathLib.abs(z) * 1e18, FixedPointMathLib.abs(x * y));
}

function testSDivWadRoundsTowardsZero(uint256 xSeed, uint256 ySeed) public {
int256 x = int256(_bound(xSeed, 0, 2e24)) - 1e24;
int256 y = int256(_bound(ySeed, 0, 2e24)) - 1e24;
if (y == 0) y = 1;
int256 z = FixedPointMathLib.sDivWad(x, y);
assertEq(z, (x * 1e18) / y);
assertEq(FixedPointMathLib.rawSDivWad(x, y), z);
assertEq(FixedPointMathLib.sDivWad(-x, y), -z);
assertLe(
FixedPointMathLib.abs(z) * FixedPointMathLib.abs(y), FixedPointMathLib.abs(x) * 1e18
);
}

function testDivWadZeroDenominatorReverts() public {
vm.expectRevert(FixedPointMathLib.DivWadFailed.selector);
this.divWad(1e18, 0);
Expand Down