safeGetPartialAmount (#1035)

* Added Test "Should transfer correct amounts when left order is fully filled and values pass isRoundingErrorCeil but fail isRoundingErrorFloor"

* Added RoundingError exception to reference function for getPartialAmount

* Added RoundingError exception to reference function for getPartialAmount

* Added isRoundingErrorCeil to getPartialAmountCeil reference funtion

* Computed new values  for "Should give right maker a better buy price when correct price is not integral" that does not have a rounding error

* Almost all tests for match orders are passing after adding isRoundingErrorCeil check

* WIP commit: Added rounding error checks to getPartialAmount

* WIP commit: Added rounding error checks to getPartialAmount

* Use safe versions of getPartialAmount

* Update Exchange internals tests

* Run linter

* Found new values for "Should transfer correct amounts when right order fill amount deviates from amount derived by `Exchange.fillOrder`"

* Fixed merge conflicts

* Run all tests

* Cleaned up some comments on match Orders tests

* Fix tests for geth

7 files changed, 442 insertions, 110 deletions

diff --git a/packages/contracts/src/2.0.0/protocol/Exchange/MixinExchangeCore.sol b/packages/contracts/src/2.0.0/protocol/Exchange/MixinExchangeCore.sol
index be163ec97..64b1f7665 100644
--- a/packages/contracts/src/2.0.0/protocol/Exchange/MixinExchangeCore.sol
+++ b/packages/contracts/src/2.0.0/protocol/Exchange/MixinExchangeCore.sol
@@ -404,16 +404,6 @@ contract MixinExchangeCore is
             safeMul(order.makerAssetAmount, takerAssetFilledAmount),
             "INVALID_FILL_PRICE"
         );
-        
-        // Validate fill order rounding
-        require(
-            !isRoundingErrorFloor(
-                takerAssetFilledAmount,
-                order.takerAssetAmount,
-                order.makerAssetAmount
-            ),
-            "ROUNDING_ERROR"
-        );
     }
 
     /// @dev Validates context for cancelOrder. Succeeds or throws.
@@ -463,17 +453,17 @@ contract MixinExchangeCore is
     {
         // Compute proportional transfer amounts
         fillResults.takerAssetFilledAmount = takerAssetFilledAmount;
-        fillResults.makerAssetFilledAmount = getPartialAmountFloor(
+        fillResults.makerAssetFilledAmount = safeGetPartialAmountFloor(
             takerAssetFilledAmount,
             order.takerAssetAmount,
             order.makerAssetAmount
         );
-        fillResults.makerFeePaid = getPartialAmountFloor(
+        fillResults.makerFeePaid = safeGetPartialAmountFloor(
             takerAssetFilledAmount,
             order.takerAssetAmount,
             order.makerFee
         );
-        fillResults.takerFeePaid = getPartialAmountFloor(
+        fillResults.takerFeePaid = safeGetPartialAmountFloor(
             takerAssetFilledAmount,
             order.takerAssetAmount,
             order.takerFee
diff --git a/packages/contracts/src/2.0.0/protocol/Exchange/MixinMatchOrders.sol b/packages/contracts/src/2.0.0/protocol/Exchange/MixinMatchOrders.sol
index 075a610b5..b4f6bdb26 100644
--- a/packages/contracts/src/2.0.0/protocol/Exchange/MixinMatchOrders.sol
+++ b/packages/contracts/src/2.0.0/protocol/Exchange/MixinMatchOrders.sol
@@ -177,13 +177,13 @@ contract MixinMatchOrders is
     {
         // Derive maker asset amounts for left & right orders, given store taker assert amounts
         uint256 leftTakerAssetAmountRemaining = safeSub(leftOrder.takerAssetAmount, leftOrderTakerAssetFilledAmount);
-        uint256 leftMakerAssetAmountRemaining = getPartialAmountFloor(
+        uint256 leftMakerAssetAmountRemaining = safeGetPartialAmountFloor(
             leftOrder.makerAssetAmount,
             leftOrder.takerAssetAmount,
             leftTakerAssetAmountRemaining
         );
         uint256 rightTakerAssetAmountRemaining = safeSub(rightOrder.takerAssetAmount, rightOrderTakerAssetFilledAmount);
-        uint256 rightMakerAssetAmountRemaining = getPartialAmountFloor(
+        uint256 rightMakerAssetAmountRemaining = safeGetPartialAmountFloor(
             rightOrder.makerAssetAmount,
             rightOrder.takerAssetAmount,
             rightTakerAssetAmountRemaining
@@ -205,7 +205,7 @@ contract MixinMatchOrders is
             matchedFillResults.left.takerAssetFilledAmount = matchedFillResults.right.makerAssetFilledAmount;
             // Round down to ensure the maker's exchange rate does not exceed the price specified by the order. 
             // We favor the maker when the exchange rate must be rounded.
-            matchedFillResults.left.makerAssetFilledAmount = getPartialAmountFloor(
+            matchedFillResults.left.makerAssetFilledAmount = safeGetPartialAmountFloor(
                 leftOrder.makerAssetAmount,
                 leftOrder.takerAssetAmount,
                 matchedFillResults.left.takerAssetFilledAmount
@@ -217,7 +217,7 @@ contract MixinMatchOrders is
             matchedFillResults.right.makerAssetFilledAmount = matchedFillResults.left.takerAssetFilledAmount;
             // Round up to ensure the maker's exchange rate does not exceed the price specified by the order.
             // We favor the maker when the exchange rate must be rounded.
-            matchedFillResults.right.takerAssetFilledAmount = getPartialAmountCeil(
+            matchedFillResults.right.takerAssetFilledAmount = safeGetPartialAmountCeil(
                 rightOrder.takerAssetAmount,
                 rightOrder.makerAssetAmount,
                 matchedFillResults.right.makerAssetFilledAmount
@@ -231,24 +231,24 @@ contract MixinMatchOrders is
         );
 
         // Compute fees for left order
-        matchedFillResults.left.makerFeePaid = getPartialAmountFloor(
+        matchedFillResults.left.makerFeePaid = safeGetPartialAmountFloor(
             matchedFillResults.left.makerAssetFilledAmount,
             leftOrder.makerAssetAmount,
             leftOrder.makerFee
         );
-        matchedFillResults.left.takerFeePaid = getPartialAmountFloor(
+        matchedFillResults.left.takerFeePaid = safeGetPartialAmountFloor(
             matchedFillResults.left.takerAssetFilledAmount,
             leftOrder.takerAssetAmount,
             leftOrder.takerFee
         );
 
         // Compute fees for right order
-        matchedFillResults.right.makerFeePaid = getPartialAmountFloor(
+        matchedFillResults.right.makerFeePaid = safeGetPartialAmountFloor(
             matchedFillResults.right.makerAssetFilledAmount,
             rightOrder.makerAssetAmount,
             rightOrder.makerFee
         );
-        matchedFillResults.right.takerFeePaid = getPartialAmountFloor(
+        matchedFillResults.right.takerFeePaid = safeGetPartialAmountFloor(
             matchedFillResults.right.takerAssetFilledAmount,
             rightOrder.takerAssetAmount,
             rightOrder.takerFee
diff --git a/packages/contracts/src/2.0.0/protocol/Exchange/libs/LibMath.sol b/packages/contracts/src/2.0.0/protocol/Exchange/libs/LibMath.sol
index 0e0fba5d2..57fd53f29 100644
--- a/packages/contracts/src/2.0.0/protocol/Exchange/libs/LibMath.sol
+++ b/packages/contracts/src/2.0.0/protocol/Exchange/libs/LibMath.sol
@@ -26,11 +26,48 @@ contract LibMath is
 {
 
     /// @dev Calculates partial value given a numerator and denominator rounded down.
+    ///      Reverts if rounding error is >= 0.1%
     /// @param numerator Numerator.
     /// @param denominator Denominator.
     /// @param target Value to calculate partial of.
     /// @return Partial value of target rounded down.
-    function getPartialAmountFloor(
+    function safeGetPartialAmountFloor(
+        uint256 numerator,
+        uint256 denominator,
+        uint256 target
+    )
+        internal
+        pure
+        returns (uint256 partialAmount)
+    {
+        require(
+            denominator > 0,
+            "DIVISION_BY_ZERO"
+        );
+
+        require(
+            !isRoundingErrorFloor(
+                numerator,
+                denominator,
+                target
+            ),
+            "ROUNDING_ERROR"
+        );
+        
+        partialAmount = safeDiv(
+            safeMul(numerator, target),
+            denominator
+        );
+        return partialAmount;
+    }
+
+    /// @dev Calculates partial value given a numerator and denominator rounded down.
+    ///      Reverts if rounding error is >= 0.1%
+    /// @param numerator Numerator.
+    /// @param denominator Denominator.
+    /// @param target Value to calculate partial of.
+    /// @return Partial value of target rounded up.
+    function safeGetPartialAmountCeil(
         uint256 numerator,
         uint256 denominator,
         uint256 target
@@ -43,7 +80,48 @@ contract LibMath is
             denominator > 0,
             "DIVISION_BY_ZERO"
         );
+
+        require(
+            !isRoundingErrorCeil(
+                numerator,
+                denominator,
+                target
+            ),
+            "ROUNDING_ERROR"
+        );
         
+        // safeDiv computes `floor(a / b)`. We use the identity (a, b integer):
+        //       ceil(a / b) = floor((a + b - 1) / b)
+        // To implement `ceil(a / b)` using safeDiv.
+        partialAmount = safeDiv(
+            safeAdd(
+                safeMul(numerator, target),
+                safeSub(denominator, 1)
+            ),
+            denominator
+        );
+        return partialAmount;
+    }
+
+    /// @dev Calculates partial value given a numerator and denominator rounded down.
+    /// @param numerator Numerator.
+    /// @param denominator Denominator.
+    /// @param target Value to calculate partial of.
+    /// @return Partial value of target rounded down.
+    function getPartialAmountFloor(
+        uint256 numerator,
+        uint256 denominator,
+        uint256 target
+    )
+        internal
+        pure
+        returns (uint256 partialAmount)
+    {
+        require(
+            denominator > 0,
+            "DIVISION_BY_ZERO"
+        );
+
         partialAmount = safeDiv(
             safeMul(numerator, target),
             denominator
@@ -69,7 +147,7 @@ contract LibMath is
             denominator > 0,
             "DIVISION_BY_ZERO"
         );
-        
+
         // safeDiv computes `floor(a / b)`. We use the identity (a, b integer):
         //       ceil(a / b) = floor((a + b - 1) / b)
         // To implement `ceil(a / b)` using safeDiv.
diff --git a/packages/contracts/src/2.0.0/test/ReentrantERC20Token/ReentrantERC20Token.sol b/packages/contracts/src/2.0.0/test/ReentrantERC20Token/ReentrantERC20Token.sol
index 8bfdd2e66..4f4e28302 100644
--- a/packages/contracts/src/2.0.0/test/ReentrantERC20Token/ReentrantERC20Token.sol
+++ b/packages/contracts/src/2.0.0/test/ReentrantERC20Token/ReentrantERC20Token.sol
@@ -25,6 +25,7 @@ import "../../protocol/Exchange/interfaces/IExchange.sol";
 import "../../protocol/Exchange/libs/LibOrder.sol";
 
 
+// solhint-disable no-unused-vars
 contract ReentrantERC20Token is
     ERC20Token
 {
diff --git a/packages/contracts/src/2.0.0/test/TestExchangeInternals/TestExchangeInternals.sol b/packages/contracts/src/2.0.0/test/TestExchangeInternals/TestExchangeInternals.sol
index da9313e02..27187f8f8 100644
--- a/packages/contracts/src/2.0.0/test/TestExchangeInternals/TestExchangeInternals.sol
+++ b/packages/contracts/src/2.0.0/test/TestExchangeInternals/TestExchangeInternals.sol
@@ -63,6 +63,42 @@ contract TestExchangeInternals is
     }
 
     /// @dev Calculates partial value given a numerator and denominator.
+    ///      Reverts if rounding error is >= 0.1%
+    /// @param numerator Numerator.
+    /// @param denominator Denominator.
+    /// @param target Value to calculate partial of.
+    /// @return Partial value of target.
+    function publicSafeGetPartialAmountFloor(
+        uint256 numerator,
+        uint256 denominator,
+        uint256 target
+    )
+        public
+        pure
+        returns (uint256 partialAmount)
+    {
+        return safeGetPartialAmountFloor(numerator, denominator, target);
+    }
+
+    /// @dev Calculates partial value given a numerator and denominator.
+    ///      Reverts if rounding error is >= 0.1%
+    /// @param numerator Numerator.
+    /// @param denominator Denominator.
+    /// @param target Value to calculate partial of.
+    /// @return Partial value of target.
+    function publicSafeGetPartialAmountCeil(
+        uint256 numerator,
+        uint256 denominator,
+        uint256 target
+    )
+        public
+        pure
+        returns (uint256 partialAmount)
+    {
+        return safeGetPartialAmountCeil(numerator, denominator, target);
+    }
+
+    /// @dev Calculates partial value given a numerator and denominator.
     /// @param numerator Numerator.
     /// @param denominator Denominator.
     /// @param target Value to calculate partial of.
diff --git a/packages/contracts/test/exchange/internal.ts b/packages/contracts/test/exchange/internal.ts
index de381fca3..c5d2fc58f 100644
--- a/packages/contracts/test/exchange/internal.ts
+++ b/packages/contracts/test/exchange/internal.ts
@@ -48,9 +48,9 @@ const overflowErrorForCall = new Error(RevertReason.Uint256Overflow);
 
 describe('Exchange core internal functions', () => {
     let testExchange: TestExchangeInternalsContract;
-    let invalidOpcodeErrorForCall: Error | undefined;
     let overflowErrorForSendTransaction: Error | undefined;
     let divisionByZeroErrorForCall: Error | undefined;
+    let roundingErrorForCall: Error | undefined;
 
     before(async () => {
         await blockchainLifecycle.startAsync();
@@ -68,12 +68,67 @@ describe('Exchange core internal functions', () => {
             await getRevertReasonOrErrorMessageForSendTransactionAsync(RevertReason.Uint256Overflow),
         );
         divisionByZeroErrorForCall = new Error(RevertReason.DivisionByZero);
-        invalidOpcodeErrorForCall = new Error(await getInvalidOpcodeErrorMessageForCallAsync());
+        roundingErrorForCall = new Error(RevertReason.RoundingError);
     });
     // Note(albrow): Don't forget to add beforeEach and afterEach calls to reset
     // the blockchain state for any tests which modify it!
 
-    async function referenceGetPartialAmountFloorAsync(
+    async function referenceIsRoundingErrorFloorAsync(
+        numerator: BigNumber,
+        denominator: BigNumber,
+        target: BigNumber,
+    ): Promise<boolean> {
+        if (denominator.eq(0)) {
+            throw divisionByZeroErrorForCall;
+        }
+        if (numerator.eq(0)) {
+            return false;
+        }
+        if (target.eq(0)) {
+            return false;
+        }
+        const product = numerator.mul(target);
+        const remainder = product.mod(denominator);
+        const remainderTimes1000 = remainder.mul('1000');
+        const isError = remainderTimes1000.gte(product);
+        if (product.greaterThan(MAX_UINT256)) {
+            throw overflowErrorForCall;
+        }
+        if (remainderTimes1000.greaterThan(MAX_UINT256)) {
+            throw overflowErrorForCall;
+        }
+        return isError;
+    }
+
+    async function referenceIsRoundingErrorCeilAsync(
+        numerator: BigNumber,
+        denominator: BigNumber,
+        target: BigNumber,
+    ): Promise<boolean> {
+        if (denominator.eq(0)) {
+            throw divisionByZeroErrorForCall;
+        }
+        if (numerator.eq(0)) {
+            return false;
+        }
+        if (target.eq(0)) {
+            return false;
+        }
+        const product = numerator.mul(target);
+        const remainder = product.mod(denominator);
+        const error = denominator.sub(remainder).mod(denominator);
+        const errorTimes1000 = error.mul('1000');
+        const isError = errorTimes1000.gte(product);
+        if (product.greaterThan(MAX_UINT256)) {
+            throw overflowErrorForCall;
+        }
+        if (errorTimes1000.greaterThan(MAX_UINT256)) {
+            throw overflowErrorForCall;
+        }
+        return isError;
+    }
+
+    async function referenceSafeGetPartialAmountFloorAsync(
         numerator: BigNumber,
         denominator: BigNumber,
         target: BigNumber,
@@ -81,6 +136,10 @@ describe('Exchange core internal functions', () => {
         if (denominator.eq(0)) {
             throw divisionByZeroErrorForCall;
         }
+        const isRoundingError = await referenceIsRoundingErrorFloorAsync(numerator, denominator, target);
+        if (isRoundingError) {
+            throw roundingErrorForCall;
+        }
         const product = numerator.mul(target);
         if (product.greaterThan(MAX_UINT256)) {
             throw overflowErrorForCall;
@@ -163,18 +222,18 @@ describe('Exchange core internal functions', () => {
             // implementation or the Solidity implementation of
             // calculateFillResults.
             return {
-                makerAssetFilledAmount: await referenceGetPartialAmountFloorAsync(
+                makerAssetFilledAmount: await referenceSafeGetPartialAmountFloorAsync(
                     takerAssetFilledAmount,
                     orderTakerAssetAmount,
                     otherAmount,
                 ),
                 takerAssetFilledAmount,
-                makerFeePaid: await referenceGetPartialAmountFloorAsync(
+                makerFeePaid: await referenceSafeGetPartialAmountFloorAsync(
                     takerAssetFilledAmount,
                     orderTakerAssetAmount,
                     otherAmount,
                 ),
-                takerFeePaid: await referenceGetPartialAmountFloorAsync(
+                takerFeePaid: await referenceSafeGetPartialAmountFloorAsync(
                     takerAssetFilledAmount,
                     orderTakerAssetAmount,
                     otherAmount,
@@ -198,6 +257,20 @@ describe('Exchange core internal functions', () => {
     });
 
     describe('getPartialAmountFloor', async () => {
+        async function referenceGetPartialAmountFloorAsync(
+            numerator: BigNumber,
+            denominator: BigNumber,
+            target: BigNumber,
+        ): Promise<BigNumber> {
+            if (denominator.eq(0)) {
+                throw divisionByZeroErrorForCall;
+            }
+            const product = numerator.mul(target);
+            if (product.greaterThan(MAX_UINT256)) {
+                throw overflowErrorForCall;
+            }
+            return product.dividedToIntegerBy(denominator);
+        }
         async function testGetPartialAmountFloorAsync(
             numerator: BigNumber,
             denominator: BigNumber,
@@ -206,7 +279,7 @@ describe('Exchange core internal functions', () => {
             return testExchange.publicGetPartialAmountFloor.callAsync(numerator, denominator, target);
         }
         await testCombinatoriallyWithReferenceFuncAsync(
-            'getPartialAmount',
+            'getPartialAmountFloor',
             referenceGetPartialAmountFloorAsync,
             testGetPartialAmountFloorAsync,
             [uint256Values, uint256Values, uint256Values],
@@ -250,76 +323,80 @@ describe('Exchange core internal functions', () => {
         );
     });
 
-    describe('isRoundingError', async () => {
-        async function referenceIsRoundingErrorAsync(
+    describe('safeGetPartialAmountFloor', async () => {
+        async function testSafeGetPartialAmountFloorAsync(
             numerator: BigNumber,
             denominator: BigNumber,
             target: BigNumber,
-        ): Promise<boolean> {
+        ): Promise<BigNumber> {
+            return testExchange.publicSafeGetPartialAmountFloor.callAsync(numerator, denominator, target);
+        }
+        await testCombinatoriallyWithReferenceFuncAsync(
+            'safeGetPartialAmountFloor',
+            referenceSafeGetPartialAmountFloorAsync,
+            testSafeGetPartialAmountFloorAsync,
+            [uint256Values, uint256Values, uint256Values],
+        );
+    });
+
+    describe('safeGetPartialAmountCeil', async () => {
+        async function referenceSafeGetPartialAmountCeilAsync(
+            numerator: BigNumber,
+            denominator: BigNumber,
+            target: BigNumber,
+        ): Promise<BigNumber> {
             if (denominator.eq(0)) {
                 throw divisionByZeroErrorForCall;
             }
-            if (numerator.eq(0)) {
-                return false;
-            }
-            if (target.eq(0)) {
-                return false;
+            const isRoundingError = await referenceIsRoundingErrorCeilAsync(numerator, denominator, target);
+            if (isRoundingError) {
+                throw roundingErrorForCall;
             }
             const product = numerator.mul(target);
-            const remainder = product.mod(denominator);
-            const remainderTimes1000 = remainder.mul('1000');
-            const isError = remainderTimes1000.gt(product);
-            if (product.greaterThan(MAX_UINT256)) {
+            const offset = product.add(denominator.sub(1));
+            if (offset.greaterThan(MAX_UINT256)) {
                 throw overflowErrorForCall;
             }
-            if (remainderTimes1000.greaterThan(MAX_UINT256)) {
-                throw overflowErrorForCall;
+            const result = offset.dividedToIntegerBy(denominator);
+            if (product.mod(denominator).eq(0)) {
+                expect(result.mul(denominator)).to.be.bignumber.eq(product);
+            } else {
+                expect(result.mul(denominator)).to.be.bignumber.gt(product);
             }
-            return isError;
+            return result;
         }
-        async function testIsRoundingErrorAsync(
+        async function testSafeGetPartialAmountCeilAsync(
             numerator: BigNumber,
             denominator: BigNumber,
             target: BigNumber,
-        ): Promise<boolean> {
-            return testExchange.publicIsRoundingErrorFloor.callAsync(numerator, denominator, target);
+        ): Promise<BigNumber> {
+            return testExchange.publicSafeGetPartialAmountCeil.callAsync(numerator, denominator, target);
         }
         await testCombinatoriallyWithReferenceFuncAsync(
-            'isRoundingError',
-            referenceIsRoundingErrorAsync,
-            testIsRoundingErrorAsync,
+            'safeGetPartialAmountCeil',
+            referenceSafeGetPartialAmountCeilAsync,
+            testSafeGetPartialAmountCeilAsync,
             [uint256Values, uint256Values, uint256Values],
         );
     });
 
-    describe('isRoundingErrorCeil', async () => {
-        async function referenceIsRoundingErrorAsync(
+    describe('isRoundingErrorFloor', async () => {
+        async function testIsRoundingErrorFloorAsync(
             numerator: BigNumber,
             denominator: BigNumber,
             target: BigNumber,
         ): Promise<boolean> {
-            if (denominator.eq(0)) {
-                throw divisionByZeroErrorForCall;
-            }
-            if (numerator.eq(0)) {
-                return false;
-            }
-            if (target.eq(0)) {
-                return false;
-            }
-            const product = numerator.mul(target);
-            const remainder = product.mod(denominator);
-            const error = denominator.sub(remainder).mod(denominator);
-            const errorTimes1000 = error.mul('1000');
-            const isError = errorTimes1000.gt(product);
-            if (product.greaterThan(MAX_UINT256)) {
-                throw overflowErrorForCall;
-            }
-            if (errorTimes1000.greaterThan(MAX_UINT256)) {
-                throw overflowErrorForCall;
-            }
-            return isError;
+            return testExchange.publicIsRoundingErrorFloor.callAsync(numerator, denominator, target);
         }
+        await testCombinatoriallyWithReferenceFuncAsync(
+            'isRoundingErrorFloor',
+            referenceIsRoundingErrorFloorAsync,
+            testIsRoundingErrorFloorAsync,
+            [uint256Values, uint256Values, uint256Values],
+        );
+    });
+
+    describe('isRoundingErrorCeil', async () => {
         async function testIsRoundingErrorCeilAsync(
             numerator: BigNumber,
             denominator: BigNumber,
@@ -329,7 +406,7 @@ describe('Exchange core internal functions', () => {
         }
         await testCombinatoriallyWithReferenceFuncAsync(
             'isRoundingErrorCeil',
-            referenceIsRoundingErrorAsync,
+            referenceIsRoundingErrorCeilAsync,
             testIsRoundingErrorCeilAsync,
             [uint256Values, uint256Values, uint256Values],
         );
diff --git a/packages/contracts/test/exchange/match_orders.ts b/packages/contracts/test/exchange/match_orders.ts
index 8732e20ba..554c456cc 100644
--- a/packages/contracts/test/exchange/match_orders.ts
+++ b/packages/contracts/test/exchange/match_orders.ts
@@ -3,6 +3,7 @@ import { assetDataUtils } from '@0xproject/order-utils';
 import { RevertReason } from '@0xproject/types';
 import { BigNumber } from '@0xproject/utils';
 import { Web3Wrapper } from '@0xproject/web3-wrapper';
+import * as chai from 'chai';
 import * as _ from 'lodash';
 
 import { DummyERC20TokenContract } from '../../generated_contract_wrappers/dummy_erc20_token';
@@ -11,8 +12,10 @@ import { ERC20ProxyContract } from '../../generated_contract_wrappers/erc20_prox
 import { ERC721ProxyContract } from '../../generated_contract_wrappers/erc721_proxy';
 import { ExchangeContract } from '../../generated_contract_wrappers/exchange';
 import { ReentrantERC20TokenContract } from '../../generated_contract_wrappers/reentrant_erc20_token';
+import { TestExchangeInternalsContract } from '../../generated_contract_wrappers/test_exchange_internals';
 import { artifacts } from '../utils/artifacts';
 import { expectTransactionFailedAsync } from '../utils/assertions';
+import { chaiSetup } from '../utils/chai_setup';
 import { constants } from '../utils/constants';
 import { ERC20Wrapper } from '../utils/erc20_wrapper';
 import { ERC721Wrapper } from '../utils/erc721_wrapper';
@@ -23,6 +26,8 @@ import { ERC20BalancesByOwner, ERC721TokenIdsByOwner } from '../utils/types';
 import { provider, txDefaults, web3Wrapper } from '../utils/web3_wrapper';
 
 const blockchainLifecycle = new BlockchainLifecycle(web3Wrapper);
+chaiSetup.configure();
+const expect = chai.expect;
 
 describe('matchOrders', () => {
     let makerAddressLeft: string;
@@ -58,6 +63,8 @@ describe('matchOrders', () => {
 
     let matchOrderTester: MatchOrderTester;
 
+    let testExchange: TestExchangeInternalsContract;
+
     before(async () => {
         await blockchainLifecycle.startAsync();
     });
@@ -160,6 +167,11 @@ describe('matchOrders', () => {
         orderFactoryRight = new OrderFactory(privateKeyRight, defaultOrderParamsRight);
         // Set match order tester
         matchOrderTester = new MatchOrderTester(exchangeWrapper, erc20Wrapper, erc721Wrapper, zrxToken.address);
+        testExchange = await TestExchangeInternalsContract.deployFrom0xArtifactAsync(
+            artifacts.TestExchangeInternals,
+            provider,
+            txDefaults,
+        );
     });
     beforeEach(async () => {
         await blockchainLifecycle.startAsync();
@@ -173,39 +185,170 @@ describe('matchOrders', () => {
             erc721TokenIdsByOwner = await erc721Wrapper.getBalancesAsync();
         });
 
-        it('Should give right maker a better price when correct price is not integral', async () => {
+        it('Should transfer correct amounts when right order is fully filled and values pass isRoundingErrorFloor but fail isRoundingErrorCeil', async () => {
+            // Create orders to match
+            const signedOrderLeft = await orderFactoryLeft.newSignedOrderAsync({
+                makerAddress: makerAddressLeft,
+                makerAssetAmount: Web3Wrapper.toBaseUnitAmount(new BigNumber(17), 0),
+                takerAssetAmount: Web3Wrapper.toBaseUnitAmount(new BigNumber(98), 0),
+                feeRecipientAddress: feeRecipientAddressLeft,
+            });
+            const signedOrderRight = await orderFactoryRight.newSignedOrderAsync({
+                makerAddress: makerAddressRight,
+                makerAssetData: assetDataUtils.encodeERC20AssetData(defaultERC20TakerAssetAddress),
+                takerAssetData: assetDataUtils.encodeERC20AssetData(defaultERC20MakerAssetAddress),
+                makerAssetAmount: Web3Wrapper.toBaseUnitAmount(new BigNumber(75), 0),
+                takerAssetAmount: Web3Wrapper.toBaseUnitAmount(new BigNumber(13), 0),
+                feeRecipientAddress: feeRecipientAddressRight,
+            });
+            // Assert is rounding error ceil & not rounding error floor
+            // These assertions are taken from MixinMatchOrders::calculateMatchedFillResults
+            // The rounding error is derived computating how much the left maker will sell.
+            const numerator = signedOrderLeft.makerAssetAmount;
+            const denominator = signedOrderLeft.takerAssetAmount;
+            const target = signedOrderRight.makerAssetAmount;
+            const isRoundingErrorCeil = await testExchange.publicIsRoundingErrorCeil.callAsync(
+                numerator,
+                denominator,
+                target,
+            );
+            expect(isRoundingErrorCeil).to.be.true();
+            const isRoundingErrorFloor = await testExchange.publicIsRoundingErrorFloor.callAsync(
+                numerator,
+                denominator,
+                target,
+            );
+            expect(isRoundingErrorFloor).to.be.false();
+            // Match signedOrderLeft with signedOrderRight
+            // Note that the left maker received a slightly better sell price.
+            // This is intentional; see note in MixinMatchOrders.calculateMatchedFillResults.
+            // Because the left maker received a slightly more favorable sell price, the fee
+            // paid by the left taker is slightly higher than that paid by the left maker.
+            // Fees can be thought of as a tax paid by the seller, derived from the sale price.
+            const expectedTransferAmounts = {
+                // Left Maker
+                amountSoldByLeftMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(13), 0),
+                amountBoughtByLeftMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(75), 0),
+                feePaidByLeftMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber('76.4705882352941176'), 16), // 76.47%
+                // Right Maker
+                amountSoldByRightMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(75), 0),
+                amountBoughtByRightMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(13), 0),
+                feePaidByRightMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(100), 16), // 100%
+                // Taker
+                amountReceivedByTaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(0), 0),
+                feePaidByTakerLeft: Web3Wrapper.toBaseUnitAmount(new BigNumber('76.5306122448979591'), 16), // 76.53%
+                feePaidByTakerRight: Web3Wrapper.toBaseUnitAmount(new BigNumber(100), 16), // 100%
+            };
+            await matchOrderTester.matchOrdersAndAssertEffectsAsync(
+                signedOrderLeft,
+                signedOrderRight,
+                takerAddress,
+                erc20BalancesByOwner,
+                erc721TokenIdsByOwner,
+                expectedTransferAmounts,
+            );
+        });
+
+        it('Should transfer correct amounts when left order is fully filled and values pass isRoundingErrorCeil but fail isRoundingErrorFloor', async () => {
+            // Create orders to match
+            const signedOrderLeft = await orderFactoryLeft.newSignedOrderAsync({
+                makerAddress: makerAddressLeft,
+                makerAssetAmount: Web3Wrapper.toBaseUnitAmount(new BigNumber(15), 0),
+                takerAssetAmount: Web3Wrapper.toBaseUnitAmount(new BigNumber(90), 0),
+                feeRecipientAddress: feeRecipientAddressLeft,
+            });
+            const signedOrderRight = await orderFactoryRight.newSignedOrderAsync({
+                makerAddress: makerAddressRight,
+                makerAssetData: assetDataUtils.encodeERC20AssetData(defaultERC20TakerAssetAddress),
+                takerAssetData: assetDataUtils.encodeERC20AssetData(defaultERC20MakerAssetAddress),
+                makerAssetAmount: Web3Wrapper.toBaseUnitAmount(new BigNumber(97), 0),
+                takerAssetAmount: Web3Wrapper.toBaseUnitAmount(new BigNumber(14), 0),
+                feeRecipientAddress: feeRecipientAddressRight,
+            });
+            // Assert is rounding error floor & not rounding error ceil
+            // These assertions are taken from MixinMatchOrders::calculateMatchedFillResults
+            // The rounding error is derived computating how much the right maker will buy.
+            const numerator = signedOrderRight.takerAssetAmount;
+            const denominator = signedOrderRight.makerAssetAmount;
+            const target = signedOrderLeft.takerAssetAmount;
+            const isRoundingErrorFloor = await testExchange.publicIsRoundingErrorFloor.callAsync(
+                numerator,
+                denominator,
+                target,
+            );
+            expect(isRoundingErrorFloor).to.be.true();
+            const isRoundingErrorCeil = await testExchange.publicIsRoundingErrorCeil.callAsync(
+                numerator,
+                denominator,
+                target,
+            );
+            expect(isRoundingErrorCeil).to.be.false();
+            // Match signedOrderLeft with signedOrderRight
+            // Note that the right maker received a slightly better purchase price.
+            // This is intentional; see note in MixinMatchOrders.calculateMatchedFillResults.
+            // Because the right maker received a slightly more favorable buy price, the fee
+            // paid by the right taker is slightly higher than that paid by the right maker.
+            // Fees can be thought of as a tax paid by the seller, derived from the sale price.
+            const expectedTransferAmounts = {
+                // Left Maker
+                amountSoldByLeftMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(15), 0),
+                amountBoughtByLeftMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(90), 0),
+                feePaidByLeftMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(100), 16), // 100%
+                // Right Maker
+                amountSoldByRightMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(90), 0),
+                amountBoughtByRightMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(13), 0),
+                feePaidByRightMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber('92.7835051546391752'), 16), // 92.78%
+                // Taker
+                amountReceivedByTaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(2), 0),
+                feePaidByTakerLeft: Web3Wrapper.toBaseUnitAmount(new BigNumber(100), 16), // 100%
+                feePaidByTakerRight: Web3Wrapper.toBaseUnitAmount(new BigNumber('92.8571428571428571'), 16), // 92.85%
+            };
+            await matchOrderTester.matchOrdersAndAssertEffectsAsync(
+                signedOrderLeft,
+                signedOrderRight,
+                takerAddress,
+                erc20BalancesByOwner,
+                erc721TokenIdsByOwner,
+                expectedTransferAmounts,
+            );
+        });
+
+        it('Should give right maker a better buy price when rounding', async () => {
             // Create orders to match
             const signedOrderLeft = await orderFactoryLeft.newSignedOrderAsync({
                 makerAddress: makerAddressLeft,
-                makerAssetAmount: Web3Wrapper.toBaseUnitAmount(new BigNumber(2000), 0),
-                takerAssetAmount: Web3Wrapper.toBaseUnitAmount(new BigNumber(1001), 0),
+                makerAssetAmount: Web3Wrapper.toBaseUnitAmount(new BigNumber(16), 0),
+                takerAssetAmount: Web3Wrapper.toBaseUnitAmount(new BigNumber(22), 0),
                 feeRecipientAddress: feeRecipientAddressLeft,
             });
             const signedOrderRight = await orderFactoryRight.newSignedOrderAsync({
                 makerAddress: makerAddressRight,
                 makerAssetData: assetDataUtils.encodeERC20AssetData(defaultERC20TakerAssetAddress),
                 takerAssetData: assetDataUtils.encodeERC20AssetData(defaultERC20MakerAssetAddress),
-                makerAssetAmount: Web3Wrapper.toBaseUnitAmount(new BigNumber(10000), 0),
-                takerAssetAmount: Web3Wrapper.toBaseUnitAmount(new BigNumber(3000), 0),
+                makerAssetAmount: Web3Wrapper.toBaseUnitAmount(new BigNumber(83), 0),
+                takerAssetAmount: Web3Wrapper.toBaseUnitAmount(new BigNumber(49), 0),
                 feeRecipientAddress: feeRecipientAddressRight,
             });
             // Note:
+            // The correct price buy price for the right maker would yield (49/83) * 22 = 12.988 units
+            // of the left maker asset. This gets rounded up to 13, giving the right maker a better price.
+            // Note:
             //  The maker/taker fee percentage paid on the right order differs because
-            //  they received different sale prices. Similarly, the right maker pays a
-            //  slightly higher lower than the right taker.
+            //  they received different sale prices. The right maker pays a
+            //  fee slightly lower than the right taker.
             const expectedTransferAmounts = {
                 // Left Maker
-                amountSoldByLeftMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(2000), 0),
-                amountBoughtByLeftMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(1001), 0),
+                amountSoldByLeftMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(16), 0),
+                amountBoughtByLeftMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(22), 0),
                 feePaidByLeftMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(100), 16), // 100%
                 // Right Maker
-                amountSoldByRightMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(1001), 0),
-                amountBoughtByRightMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(301), 0),
-                feePaidByRightMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(10.01), 16), // 10.01%
+                amountSoldByRightMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(22), 0),
+                amountBoughtByRightMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(13), 0),
+                feePaidByRightMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber('26.5060240963855421'), 16), // 26.506%
                 // Taker
-                amountReceivedByTaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(1699), 0),
+                amountReceivedByTaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(3), 0),
                 feePaidByTakerLeft: Web3Wrapper.toBaseUnitAmount(new BigNumber(100), 16), // 100%
-                feePaidByTakerRight: Web3Wrapper.toBaseUnitAmount(new BigNumber('10.0333333333333333'), 16), // 10.03%
+                feePaidByTakerRight: Web3Wrapper.toBaseUnitAmount(new BigNumber('26.5306122448979591'), 16), // 26.531%
             };
             // Match signedOrderLeft with signedOrderRight
             await matchOrderTester.matchOrdersAndAssertEffectsAsync(
@@ -218,7 +361,7 @@ describe('matchOrders', () => {
             );
         });
 
-        it('Should give left maker a better price when correct price is not integral', async () => {
+        it('Should give left maker a better sell price when rounding', async () => {
             // Create orders to match
             const signedOrderLeft = await orderFactoryLeft.newSignedOrderAsync({
                 makerAddress: makerAddressLeft,
@@ -236,7 +379,8 @@ describe('matchOrders', () => {
             });
             // Note:
             //  The maker/taker fee percentage paid on the left order differs because
-            //  they received different sale prices.
+            //  they received different sale prices. The left maker pays a fee
+            //  slightly lower than the left taker.
             const expectedTransferAmounts = {
                 // Left Maker
                 amountSoldByLeftMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(11), 0),
@@ -266,39 +410,45 @@ describe('matchOrders', () => {
             // Create orders to match
             const signedOrderLeft = await orderFactoryLeft.newSignedOrderAsync({
                 makerAddress: makerAddressLeft,
-                makerAssetAmount: Web3Wrapper.toBaseUnitAmount(new BigNumber(10), 0),
-                takerAssetAmount: Web3Wrapper.toBaseUnitAmount(new BigNumber(3), 0),
+                makerAssetAmount: Web3Wrapper.toBaseUnitAmount(new BigNumber(1000), 0),
+                takerAssetAmount: Web3Wrapper.toBaseUnitAmount(new BigNumber(1005), 0),
                 feeRecipientAddress: feeRecipientAddressLeft,
             });
             const signedOrderRight = await orderFactoryRight.newSignedOrderAsync({
                 makerAddress: makerAddressRight,
                 makerAssetData: assetDataUtils.encodeERC20AssetData(defaultERC20TakerAssetAddress),
                 takerAssetData: assetDataUtils.encodeERC20AssetData(defaultERC20MakerAssetAddress),
-                makerAssetAmount: Web3Wrapper.toBaseUnitAmount(new BigNumber(4), 0),
-                takerAssetAmount: Web3Wrapper.toBaseUnitAmount(new BigNumber(2), 0),
+                makerAssetAmount: Web3Wrapper.toBaseUnitAmount(new BigNumber(2126), 0),
+                takerAssetAmount: Web3Wrapper.toBaseUnitAmount(new BigNumber(1063), 0),
                 feeRecipientAddress: feeRecipientAddressRight,
             });
-            // TODO: These values will change after implementation of rounding up has been merged
             const expectedTransferAmounts = {
                 // Left Maker
-                amountSoldByLeftMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(10), 0),
-                amountBoughtByLeftMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(3), 0),
+                amountSoldByLeftMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(1000), 0),
+                amountBoughtByLeftMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(1005), 0),
                 feePaidByLeftMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(100), 16), // 100%
                 // Right Maker
-                // Note:
-                //  For order [4,2] valid fill amounts through `Exchange.fillOrder` would be [2, 1] or [4, 2]
-                //  In this case we have fill amounts of [3, 1] which is attainable through
-                // `Exchange.matchOrders` but not `Exchange.fillOrder`
-                // Note:
-                //  The right maker fee differs from the right taker fee because their exchange rate differs.
-                //  The right maker always receives the better exchange and fee price.
-                amountSoldByRightMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(3), 0),
-                amountBoughtByRightMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(2), 0),
-                feePaidByRightMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(75), 16), // 75%
+                // Notes:
+                //  i.
+                //    The left order is fully filled by the right order, so the right maker must sell 1005 units of their asset to the left maker.
+                //    By selling 1005 units, the right maker should theoretically receive 502.5 units of the left maker's asset.
+                //    Since the transfer amount must be an integer, this value must be rounded down to 502 or up to 503.
+                //  ii.
+                //    If the right order were filled via `Exchange.fillOrder` the respective fill amounts would be [1004, 502] or [1006, 503].
+                //    It follows that we cannot trigger a sale of 1005 units of the right maker's asset through `Exchange.fillOrder`.
+                //  iii.
+                //    For an optimal match, the algorithm must choose either [1005, 502] or [1005, 503] as fill amounts for the right order.
+                //    The algorithm favors the right maker when the exchange rate must be rounded, so the final fill for the right order is [1005, 503].
+                //  iv.
+                //    The right maker fee differs from the right taker fee because their exchange rate differs.
+                //    The right maker always receives the better exchange and fee price.
+                amountSoldByRightMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(1005), 0),
+                amountBoughtByRightMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(503), 0),
+                feePaidByRightMaker: Web3Wrapper.toBaseUnitAmount(new BigNumber('47.2718720602069614'), 16), // 47.27%
                 // Taker
-                amountReceivedByTaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(8), 0),
+                amountReceivedByTaker: Web3Wrapper.toBaseUnitAmount(new BigNumber(497), 0),
                 feePaidByTakerLeft: Web3Wrapper.toBaseUnitAmount(new BigNumber(100), 16), // 100%
-                feePaidByTakerRight: Web3Wrapper.toBaseUnitAmount(new BigNumber(100), 16), // 100%
+                feePaidByTakerRight: Web3Wrapper.toBaseUnitAmount(new BigNumber('47.3189087488240827'), 16), // 47.31%
             };
             // Match signedOrderLeft with signedOrderRight
             await matchOrderTester.matchOrdersAndAssertEffectsAsync(