Less Assembly. More Solidity. Less Efficiency. More Readability.

4 files changed, 306 insertions, 266 deletions

diff --git a/contracts/extensions/contracts/BalanceThresholdFilter/BalanceThresholdFilter.sol b/contracts/extensions/contracts/BalanceThresholdFilter/BalanceThresholdFilter.sol
index a68f6805d..ea248793f 100644
--- a/contracts/extensions/contracts/BalanceThresholdFilter/BalanceThresholdFilter.sol
+++ b/contracts/extensions/contracts/BalanceThresholdFilter/BalanceThresholdFilter.sol
@@ -24,21 +24,23 @@ import "./interfaces/IThresholdAsset.sol";
 import "./MixinBalanceThresholdFilterCore.sol";
 
 
-contract BalanceThresholdFilter is MixinBalanceThresholdFilterCore {
+contract BalanceThresholdFilter is
+    MixinBalanceThresholdFilterCore
+{
 
     /// @dev Constructs BalanceThresholdFilter.
     /// @param exchange Address of 0x exchange.
     /// @param thresholdAsset The asset that must be held by makers/takers.
-    /// @param thresholdBalance The minimum balance of `thresholdAsset` that must be held by makers/takers.
+    /// @param balanceThreshold The minimum balance of `thresholdAsset` that must be held by makers/takers.
     constructor(
         address exchange,
         address thresholdAsset,
-        uint256 thresholdBalance
+        uint256 balanceThreshold
     )
         public
     {
         EXCHANGE = IExchange(exchange);
         THRESHOLD_ASSET = IThresholdAsset(thresholdAsset);
-        THRESHOLD_BALANCE = thresholdBalance;
+        BALANCE_THRESHOLD = balanceThreshold;
     }
 }
diff --git a/contracts/extensions/contracts/BalanceThresholdFilter/MixinBalanceThresholdFilterCore.sol b/contracts/extensions/contracts/BalanceThresholdFilter/MixinBalanceThresholdFilterCore.sol
index 51dbae8f3..e78f9ced8 100644
--- a/contracts/extensions/contracts/BalanceThresholdFilter/MixinBalanceThresholdFilterCore.sol
+++ b/contracts/extensions/contracts/BalanceThresholdFilter/MixinBalanceThresholdFilterCore.sol
@@ -6,7 +6,7 @@
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at
 
-    http://www.apache.org/licenses/LICENSE-2.0
+    http://www.apache.org/licenses/LICENSE2.0
 
   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
@@ -17,31 +17,36 @@
 */
 
 pragma solidity 0.4.24;
-pragma experimental ABIEncoderV2;
 
 import "./mixins/MBalanceThresholdFilterCore.sol";
+import "@0x/contracts-utils/contracts/utils/ExchangeSelectors/ExchangeSelectors.sol";
+import "@0x/contracts-libs/contracts/libs/LibOrder.sol";
 
 
-contract MixinBalanceThresholdFilterCore is MBalanceThresholdFilterCore {
+contract MixinBalanceThresholdFilterCore is
+    MBalanceThresholdFilterCore,
+    LibOrder,
+    ExchangeSelectors
+{
 
     /// @dev Executes an Exchange transaction iff the maker and taker meet 
     ///      the hold at least `BALANCE_THRESHOLD` of the asset `THRESHOLD_ASSET` OR 
     ///      the exchange function is a cancellation.
     ///      Supported Exchange functions:
-    ///         - batchFillOrders
-    ///         - batchFillOrdersNoThrow
-    ///         - batchFillOrKillOrders
-    ///         - fillOrder
-    ///         - fillOrderNoThrow
-    ///         - fillOrKillOrder
-    ///         - marketBuyOrders
-    ///         - marketBuyOrdersNoThrow
-    ///         - marketSellOrders
-    ///         - marketSellOrdersNoThrow
-    ///         - matchOrders
-    ///         - cancelOrder
-    ///         - batchCancelOrders
-    ///         - cancelOrdersUpTo
+    ///          batchFillOrders
+    ///          batchFillOrdersNoThrow
+    ///          batchFillOrKillOrders
+    ///          fillOrder
+    ///          fillOrderNoThrow
+    ///          fillOrKillOrder
+    ///          marketBuyOrders
+    ///          marketBuyOrdersNoThrow
+    ///          marketSellOrders
+    ///          marketSellOrdersNoThrow
+    ///          matchOrders
+    ///          cancelOrder
+    ///          batchCancelOrders
+    ///          cancelOrdersUpTo
     ///     Trying to call any other exchange function will throw.
     /// @param salt Arbitrary number to ensure uniqueness of transaction hash.
     /// @param signerAddress Address of transaction signer.
@@ -56,7 +61,7 @@ contract MixinBalanceThresholdFilterCore is MBalanceThresholdFilterCore {
         external
     {
         // Validate addresses.
-        validateBalanceThresholdsOrRevert();
+        validateBalanceThresholdsOrRevert(signerAddress);
         
         // All addresses are valid. Execute fillOrder.
         EXCHANGE.executeTransaction(
@@ -67,6 +72,83 @@ contract MixinBalanceThresholdFilterCore is MBalanceThresholdFilterCore {
         );
     }
 
+    /// @dev Emulates the `calldataload` opcode on the embedded Exchange calldata,
+    ///      which is accessed through `signedExchangeTransaction`.
+    /// @param offset  Offset into the Exchange calldata.
+    /// @return value  Corresponding 32 byte value stored at `offset`.
+    function exchangeCalldataload(uint256 offset)
+        internal
+        returns (bytes32 value)
+    {
+        assembly {
+            // Pointer to exchange transaction
+            // 0x04 for calldata selector
+            // 0x40 to access `signedExchangeTransaction`, which is the third parameter
+            let exchangeTxPtr := calldataload(0x44)
+
+            // Offset into Exchange calldata
+            // We compute this by adding 0x24 to the `exchangeTxPtr` computed above.
+            // 0x04 for calldata selector
+            // 0x20 for length field of `signedExchangeTransaction`
+            let exchangeCalldataOffset := add(exchangeTxPtr, add(0x24, offset))
+            value := calldataload(exchangeCalldataOffset)
+        }
+    }
+
+    /// @dev Convenience function that skips the 4 byte selector when loading
+    ///      from the embedded Exchange calldata.
+    /// @param offset  Offset into the Exchange calldata (minus the 4 byte selector)
+    /// @return value  Corresponding 32 byte value stored at `offset` + 4.
+    function loadExchangeData(uint256 offset)
+        internal
+        returns (bytes32 value)
+    {
+        value = exchangeCalldataload(offset + 4);
+    }
+
+    /// @dev A running list is maintained of addresses to validate. 
+    ///     This function records an address in this array.
+    /// @param addressToValidate  Address to record for validation.
+    function recordAddressToValidate(address addressToValidate, address[] memory addressList) 
+        internal
+    {
+        uint256 newAddressListLength = addressList.length + 1;
+        assembly {
+            // Store new array length
+            mstore(addressList, newAddressListLength)
+            mstore(0x40, add(addressList, add(0x20, mul(0x20, newAddressListLength))))
+        }
+        addressList[newAddressListLength - 1] = addressToValidate;
+    }
+
+    /// @dev Extracts the maker address from an order stored in the Exchange calldata
+    ///      (which is embedded in `signedExchangeTransaction`), and records it in
+    ///      the running list of addresses to validate.
+    /// @param orderParamIndex  Index of the order in the Exchange function's signature
+    function loadMakerAddressFromOrder(uint8 orderParamIndex) internal returns (address makerAddress) {
+        uint256 orderPtr = uint256(loadExchangeData(orderParamIndex * 0x20));
+        makerAddress = address(loadExchangeData(orderPtr));
+    }
+
+    /// @dev Extracts the maker addresses from an array of orders stored in the Exchange calldata
+    ///      (which is embedded in `signedExchangeTransaction`), and records them in
+    ///      the running list of addresses to validate.
+    /// @param orderArrayParamIndex  Index of the order array in the Exchange function's signature
+    function loadMakerAddressesFromOrderArray(uint8 orderArrayParamIndex)
+        internal
+        returns (address[] makerAddresses)
+    {
+        uint256 orderArrayPtr = uint256(loadExchangeData(orderArrayParamIndex * 0x20));
+        uint256 orderArrayLength = uint256(loadExchangeData(orderArrayPtr));
+        uint256 orderArrayElementPtr = orderArrayPtr + 0x20;
+        uint256 orderArrayElementEndPtr = orderArrayElementPtr + (orderArrayLength * 0x20);
+        for(uint orderPtrOffset = orderArrayElementPtr; orderPtrOffset < orderArrayElementEndPtr; orderPtrOffset += 0x20) {
+            uint256 orderPtr = uint256(loadExchangeData(orderPtrOffset));
+            address makerAddress = address(loadExchangeData(orderPtr + orderArrayElementPtr));
+            recordAddressToValidate(makerAddress, makerAddresses);
+        }
+    }
+
     /// @dev Validates addresses meet the balance threshold specified by `BALANCE_THRESHOLD`
     ///      for the asset `THRESHOLD_ASSET`. If one address does not meet the thresold
     ///      then this function will revert. Which addresses are validated depends on
@@ -74,250 +156,56 @@ contract MixinBalanceThresholdFilterCore is MBalanceThresholdFilterCore {
     ///      No parameters are taken as this function reads arguments directly from calldata, to save gas.
     ///      If all addresses are valid then this function emits a ValidatedAddresses event, listing all
     ///      of the addresses whose balance thresholds it checked.
-    function validateBalanceThresholdsOrRevert()
+    function validateBalanceThresholdsOrRevert(address signerAddress)
         internal
     {
-        // Addresses that are validated below.
-        address[] memory validatedAddresses;
-
-        ///// Do not add variables after this point.         /////
-        ///// The assembly block may overwrite their values. /////
-
-        // Validate addresses
-        assembly {
-             /// @dev Emulates the `calldataload` opcode on the embedded Exchange calldata,
-             ///      which is accessed through `signedExchangeTransaction`.
-             /// @param offset - Offset into the Exchange calldata.
-             /// @return value - Corresponding 32 byte value stored at `offset`.
-            function exchangeCalldataload(offset) -> value {
-                // Pointer to exchange transaction
-                // 0x04 for calldata selector
-                // 0x40 to access `signedExchangeTransaction`, which is the third parameter
-                let exchangeTxPtr := calldataload(0x44)
-
-                // Offset into Exchange calldata
-                // We compute this by adding 0x24 to the `exchangeTxPtr` computed above.
-                // 0x04 for calldata selector
-                // 0x20 for length field of `signedExchangeTransaction`
-                let exchangeCalldataOffset := add(exchangeTxPtr, add(0x24, offset))
-                value := calldataload(exchangeCalldataOffset)
-            }
-
-            /// @dev Convenience function that skips the 4 byte selector when loading
-            ///      from the embedded Exchange calldata.
-            /// @param offset - Offset into the Exchange calldata (minus the 4 byte selector)
-            /// @return value - Corresponding 32 byte value stored at `offset` + 4.
-            function loadExchangeData(offset) -> value {
-                value := exchangeCalldataload(add(offset, 0x4))
-            }
-
-             /// @dev A running list is maintained of addresses to validate. 
-             ///     This function records an address in this array.
-             /// @param addressToValidate - Address to record for validation.
-            function recordAddressToValidate(addressToValidate) {
-                // Compute `addressesToValidate` memory offset
-                let addressesToValidate_ := mload(0x40)
-                let nAddressesToValidate_ := mload(addressesToValidate_)
-
-                // Increment length
-                nAddressesToValidate_ := add(mload(addressesToValidate_), 0x01)
-                mstore(addressesToValidate_, nAddressesToValidate_)
-
-                // Append address to validate
-                let offset := mul(nAddressesToValidate_, 0x20)
-                mstore(add(addressesToValidate_, offset), addressToValidate)
-            }
-
-             /// @dev Extracts the maker address from an order stored in the Exchange calldata
-             ///      (which is embedded in `signedExchangeTransaction`), and records it in
-             ///      the running list of addresses to validate.
-             /// @param orderParamIndex - Index of the order in the Exchange function's signature
-            function recordMakerAddressFromOrder(orderParamIndex) {
-                let orderPtr := loadExchangeData(mul(orderParamIndex, 0x20))
-                let makerAddress := loadExchangeData(orderPtr)
-                recordAddressToValidate(makerAddress)
-            }
-
-            /// @dev Extracts the maker addresses from an array of orders stored in the Exchange calldata
-            ///      (which is embedded in `signedExchangeTransaction`), and records them in
-            ///      the running list of addresses to validate.
-            /// @param orderArrayParamIndex - Index of the order array in the Exchange function's signature
-            function recordMakerAddressesFromOrderArray(orderArrayParamIndex) {
-                let orderArrayPtr := loadExchangeData(mul(orderArrayParamIndex, 0x20))
-                let orderArrayLength := loadExchangeData(orderArrayPtr)
-                let orderArrayElementPtr := add(orderArrayPtr, 0x20)
-                let orderArrayElementEndPtr := add(orderArrayElementPtr, mul(orderArrayLength, 0x20))
-                for {let orderPtrOffset := orderArrayElementPtr} lt(orderPtrOffset, orderArrayElementEndPtr) {orderPtrOffset := add(orderPtrOffset, 0x20)} {
-                    let orderPtr := loadExchangeData(orderPtrOffset)
-                    let makerAddress := loadExchangeData(add(orderPtr, orderArrayElementPtr))
-                    recordAddressToValidate(makerAddress)
-                }
-            }
-
-            /// @dev Records address of signer in the running list of addresses to validate.
-            /// @note: We cannot access `signerAddress` directly from within the asm function,
-            ///        so it is loaded from the calldata.
-            function recordSignerAddress() {
-                // Load the signer address from calldata
-                // 0x04 for selector
-                // 0x20 to access `signerAddress`, which is the second parameter.
-                let signerAddress_ := calldataload(0x24)
-                recordAddressToValidate(signerAddress_)
-            }
-
-            /// @dev Records addresses to be validated when Exchange transaction is a batch fill variant.
-            ///      This is one of: batchFillOrders, batchFillOrKillOrders, batchFillNoThrow
-            ///      Reference signature<T>: <batchFillVariant>(Order[],uint256[],bytes[])
-            function recordAddressesForBatchFillVariant() {
-                // Record maker addresses from order array (parameter index 0)
-                // The signer is the taker for these orders and must also be validated.
-                recordMakerAddressesFromOrderArray(0)
-                recordSignerAddress()
-            }
-
-            /// @dev Records addresses to be validated when Exchange transaction is a fill order variant.
-            ///      This is one of: fillOrder, fillOrKillOrder, fillOrderNoThrow
-            ///      Reference signature<T>: <fillOrderVariant>(Order,uint256,bytes)
-            function recordAddressesForFillOrderVariant() {
-                // Record maker address from the order (param index 0)
-                // The signer is the taker for this order and must also be validated.
-                recordMakerAddressFromOrder(0)
-                recordSignerAddress()
-            }
-
-            /// @dev Records addresses to be validated when Exchange transaction is a market fill variant.
-            ///      This is one of: marketBuyOrders, marketBuyOrdersNoThrow, marketSellOrders, marketSellOrdersNoThrow
-            ///      Reference signature<T>: <marketFillInvariant>(Order[],uint256,bytes[])
-            function recordAddressesForMarketFillVariant() {
-                // Record maker addresses from order array (parameter index 0)
-                // The signer is the taker for these orders and must also be validated.
-                recordMakerAddressesFromOrderArray(0)
-                recordSignerAddress()
-            }
-
-            /// @dev Records addresses to be validated when Exchange transaction is matchOrders.
-            ///      Reference signature: matchOrders(Order,Order)
-            function recordAddressesForMatchOrders() {
-                // Record maker address from both orders (param indices 0 & 1).
-                // The signer is the taker and must also be validated.
-                recordMakerAddressFromOrder(0)
-                recordMakerAddressFromOrder(1)
-                recordSignerAddress()
-            }
-
-            ///// Record Addresses to Validate /////
-
-            // Addresses needing validation depends on which Exchange function is being called.
-            // Step 1/2 Read the exchange function selector.
-            let exchangeFunctionSelector := and(
-                exchangeCalldataload(0x0),
-                0xffffffff00000000000000000000000000000000000000000000000000000000
-            )
-
-            // Step 2/2 Extract addresses to validate based on this selector.
-            //          See ../../utils/ExchangeSelectors/ExchangeSelectors.sol for selectors
-            // solhint-disable no-empty-blocks
-            switch exchangeFunctionSelector
-            case 0x297bb70b00000000000000000000000000000000000000000000000000000000 { recordAddressesForBatchFillVariant() }    // batchFillOrders
-            case 0x50dde19000000000000000000000000000000000000000000000000000000000 { recordAddressesForBatchFillVariant() }    // batchFillOrdersNoThrow
-            case 0x4d0ae54600000000000000000000000000000000000000000000000000000000 { recordAddressesForBatchFillVariant() }    // batchFillOrKillOrders
-            case 0xb4be83d500000000000000000000000000000000000000000000000000000000 { recordAddressesForFillOrderVariant() }    // fillOrder
-            case 0x3e228bae00000000000000000000000000000000000000000000000000000000 { recordAddressesForFillOrderVariant() }    // fillOrderNoThrow
-            case 0x64a3bc1500000000000000000000000000000000000000000000000000000000 { recordAddressesForFillOrderVariant() }    // fillOrKillOrder
-            case 0xe5fa431b00000000000000000000000000000000000000000000000000000000 { recordAddressesForMarketFillVariant() }   // marketBuyOrders
-            case 0xa3e2038000000000000000000000000000000000000000000000000000000000 { recordAddressesForMarketFillVariant() }   // marketBuyOrdersNoThrow
-            case 0x7e1d980800000000000000000000000000000000000000000000000000000000 { recordAddressesForMarketFillVariant() }   // marketSellOrders
-            case 0xdd1c7d1800000000000000000000000000000000000000000000000000000000 { recordAddressesForMarketFillVariant() }   // marketSellOrdersNoThrow
-            case 0x3c28d86100000000000000000000000000000000000000000000000000000000 { recordAddressesForMatchOrders() }         // matchOrders
-            case 0xd46b02c300000000000000000000000000000000000000000000000000000000 {}                                          // cancelOrder
-            case 0x4ac1478200000000000000000000000000000000000000000000000000000000 {}                                          // batchCancelOrders
-            case 0x4f9559b100000000000000000000000000000000000000000000000000000000 {}                                          // cancelOrdersUpTo
-            default {
-                // Revert with `Error("INVALID_OR_BLOCKED_EXCHANGE_SELECTOR")`
-                mstore(0x00, 0x08c379a000000000000000000000000000000000000000000000000000000000)
-                mstore(0x20, 0x0000002000000000000000000000000000000000000000000000000000000000)
-                mstore(0x40, 0x00000024494e56414c49445f4f525f424c4f434b45445f45584348414e47455f)
-                mstore(0x60, 0x53454c4543544f52000000000000000000000000000000000000000000000000)
-                mstore(0x80, 0x00000000)
-                // Revert length calculation:
-                // 4   -- error selector
-                // 32  -- offset to string
-                // 32  -- string length field
-                // 64  -- strlen(INVALID_OR_BLOCKED_EXCHANGE_SELECTOR) rounded up to nearest 32-byte word.
-                revert(0, 132)
-            }
-            // solhint-enable no-empty-blocks
-
-            ///// Validate Recorded Addresses /////
-
-            // Load from memory the addresses to validate
-            let addressesToValidate := mload(0x40)
-            let addressesToValidateLength := mload(addressesToValidate)
-            let addressesToValidateElementPtr := add(addressesToValidate, 0x20)
-            let addressesToValidateElementEndPtr := add(addressesToValidateElementPtr, mul(addressesToValidateLength, 0x20))
-
-            // Set free memory pointer to after `addressesToValidate` array.
-            // This is to avoid corruption when making calls in the loop below.
-            let freeMemPtr := addressesToValidateElementEndPtr
-            mstore(0x40, freeMemPtr)
-
-            // Validate addresses
-            let thresholdAssetAddress := sload(THRESHOLD_ASSET_slot)
-            let thresholdBalance := sload(THRESHOLD_BALANCE_slot)
-            // solhint-disable max-line-length 
-            for {let addressToValidate := addressesToValidateElementPtr} lt(addressToValidate, addressesToValidateElementEndPtr) {addressToValidate := add(addressToValidate, 0x20)} {
-                // solhint-enable max-line-length 
-                // Construct calldata for `THRESHOLD_ASSET.balanceOf`
-                mstore(freeMemPtr, 0x70a0823100000000000000000000000000000000000000000000000000000000)
-                mstore(add(freeMemPtr, 0x04), mload(addressToValidate))
-               
-                // call `THRESHOLD_ASSET.balanceOf`
-                let success := call(
-                    gas,                                    // forward all gas
-                    thresholdAssetAddress,                 // call address of asset proxy
-                    0,                                      // don't send any ETH
-                    freeMemPtr,                             // pointer to start of input
-                    0x24,                                   // length of input (one padded address) 
-                    freeMemPtr,                             // write output to next free memory offset
-                    0x20                                    // reserve space for return balance (0x20 bytes)
-                )
-                if eq(success, 0) {
-                    // @TODO Revert with `Error("BALANCE_QUERY_FAILED")`
-                    mstore(0x00, 0x08c379a000000000000000000000000000000000000000000000000000000000)
-                    mstore(0x20, 0x0000002000000000000000000000000000000000000000000000000000000000)
-                    mstore(0x40, 0x0000001442414c414e43455f51554552595f4641494c45440000000000000000)
-                    mstore(0x60, 0x00000000)
-                    // Revert length calculation:
-                    // 4   -- error selector
-                    // 32  -- offset to string
-                    // 32  -- string length field
-                    // 32  -- strlen(BALANCE_QUERY_FAILED) rounded up to nearest 32-byte word.
-                    revert(0, 100)
-                }
+        // Extract addresses to validate from Exchange calldata
+        address[] memory addressesToValidate = new address[](0);
+        bytes4 exchangeFunctionSelector = bytes4(exchangeCalldataload(0));
+        if(
+            exchangeFunctionSelector == batchFillOrdersSelector         || 
+            exchangeFunctionSelector == batchFillOrdersNoThrowSelector  || 
+            exchangeFunctionSelector == batchFillOrKillOrdersSelector   ||
+            exchangeFunctionSelector == marketBuyOrdersSelector         ||
+            exchangeFunctionSelector == marketBuyOrdersNoThrowSelector  ||
+            exchangeFunctionSelector == marketSellOrdersSelector        ||
+            exchangeFunctionSelector == marketSellOrdersNoThrowSelector
+        ) {
+            addressesToValidate = loadMakerAddressesFromOrderArray(0);
+            recordAddressToValidate(signerAddress, addressesToValidate);
+        } else if(
+            exchangeFunctionSelector == fillOrderSelector           ||
+            exchangeFunctionSelector == fillOrderNoThrowSelector    ||
+            exchangeFunctionSelector == fillOrKillOrderSelector
+        ) {
+            address makerAddress = loadMakerAddressFromOrder(0);
+            recordAddressToValidate(makerAddress, addressesToValidate);
+            recordAddressToValidate(signerAddress, addressesToValidate);
+        } else if(exchangeFunctionSelector == matchOrdersSelector) {
+            address leftOrderAddress = loadMakerAddressFromOrder(0);
+            recordAddressToValidate(leftOrderAddress, addressesToValidate);
+            address rightOrderAddress = loadMakerAddressFromOrder(1);
+            recordAddressToValidate(rightOrderAddress, addressesToValidate);
+            recordAddressToValidate(signerAddress, addressesToValidate);
+        } else if(
+            exchangeFunctionSelector == cancelOrderSelector         || 
+            exchangeFunctionSelector == batchCancelOrdersSelector   ||
+            exchangeFunctionSelector == cancelOrdersUpToSelector
+        ) {
+            // Do nothing
+        } else {
+            revert("INVALID_OR_BLOCKED_EXCHANGE_SELECTOR");
+        }
 
-                // Revert if balance not held
-                let addressBalance := mload(freeMemPtr)
-                if lt(addressBalance, thresholdBalance) {
-                    // Revert with `Error("AT_LEAST_ONE_ADDRESS_DOES_NOT_MEET_BALANCE_THRESHOLD")`
-                    mstore(0x00, 0x08c379a000000000000000000000000000000000000000000000000000000000)
-                    mstore(0x20, 0x0000002000000000000000000000000000000000000000000000000000000000)
-                    mstore(0x40, 0x0000003441545f4c454153545f4f4e455f414444524553535f444f45535f4e4f)
-                    mstore(0x60, 0x545f4d4545545f42414c414e43455f5448524553484f4c440000000000000000)
-                    mstore(0x80, 0x00000000)
-                    // Revert length calculation:
-                    // 4   -- error selector
-                    // 32  -- offset to string
-                    // 32  -- string length field
-                    // 64  -- strlen(AT_LEAST_ONE_ADDRESS_DOES_NOT_MEET_BALANCE_THRESHOLD) rounded up to nearest 32-byte word.
-                    revert(0, 132)
-                }
+        // Validate account balances
+        uint256 balanceThreshold = BALANCE_THRESHOLD;
+        IThresholdAsset thresholdAsset = THRESHOLD_ASSET;
+        for(uint i = 0; i < addressesToValidate.length; ++i) {
+            uint256 addressBalance = thresholdAsset.balanceOf(addressesToValidate[i]);
+            if (addressBalance < balanceThreshold) {
+                revert("AT_LEAST_ONE_ADDRESS_DOES_NOT_MEET_BALANCE_THRESHOLD");
             }
-
-            // Record validated addresses
-            validatedAddresses := addressesToValidate
         }
-
-        ///// If we hit this point then all addresses are valid /////
-        emit ValidatedAddresses(validatedAddresses);
+        emit ValidatedAddresses(addressesToValidate);
     }
 }
diff --git a/contracts/extensions/contracts/BalanceThresholdFilter/mixins/MBalanceThresholdFilterCore.sol b/contracts/extensions/contracts/BalanceThresholdFilter/mixins/MBalanceThresholdFilterCore.sol
index af7a9453b..6aaa729fb 100644
--- a/contracts/extensions/contracts/BalanceThresholdFilter/mixins/MBalanceThresholdFilterCore.sol
+++ b/contracts/extensions/contracts/BalanceThresholdFilter/mixins/MBalanceThresholdFilterCore.sol
@@ -17,7 +17,6 @@
 */
 
 pragma solidity 0.4.24;
-pragma experimental ABIEncoderV2;
 
 import "@0x/contracts-interfaces/contracts/protocol/Exchange/IExchange.sol";
 import "../interfaces/IThresholdAsset.sol";
@@ -33,10 +32,10 @@ contract MBalanceThresholdFilterCore {
     IThresholdAsset internal THRESHOLD_ASSET;
 
     // The minimum balance of `THRESHOLD_ASSET` that must be held by makers/takers
-    uint256 internal THRESHOLD_BALANCE;
+    uint256 internal BALANCE_THRESHOLD;
     // solhint-enable var-name-mixedcase
 
-    // Addresses that hold at least `THRESHOLD_BALANCE` of `THRESHOLD_ASSET`
+    // Addresses that hold at least `BALANCE_THRESHOLD` of `THRESHOLD_ASSET`
     event ValidatedAddresses (
         address[] addresses
     );
@@ -79,5 +78,5 @@ contract MBalanceThresholdFilterCore {
     ///      No parameters are taken as this function reads arguments directly from calldata, to save gas.
     ///      If all addresses are valid then this function emits a ValidatedAddresses event, listing all
     ///      of the addresses whose balance thresholds it checked.
-    function validateBalanceThresholdsOrRevert() internal;
+    function validateBalanceThresholdsOrRevert(address signerAddress) internal;
 }
diff --git a/contracts/utils/contracts/utils/ExchangeSelectors/ExchangeSelectors.sol b/contracts/utils/contracts/utils/ExchangeSelectors/ExchangeSelectors.sol
new file mode 100644
index 000000000..c361fd075
--- /dev/null
+++ b/contracts/utils/contracts/utils/ExchangeSelectors/ExchangeSelectors.sol
@@ -0,0 +1,151 @@
+/*
+
+  Copyright 2018 ZeroEx Intl.
+
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+
+*/
+
+pragma solidity 0.4.24;
+
+
+contract ExchangeSelectors {
+
+  // allowedValidators
+  bytes4 constant allowedValidatorsSelector = 0x7b8e3514;
+  bytes4 constant allowedValidatorsSelectorGenerator = bytes4(keccak256('allowedValidators(address,address)'));
+
+  // assetProxies
+  bytes4 constant assetProxiesSelector = 0x3fd3c997;
+  bytes4 constant assetProxiesSelectorGenerator = bytes4(keccak256('assetProxies(bytes4)'));
+
+  // batchCancelOrders
+  bytes4 constant batchCancelOrdersSelector = 0x4ac14782;
+  bytes4 constant batchCancelOrdersSelectorGenerator = bytes4(keccak256('batchCancelOrders((address,address,address,address,uint256,uint256,uint256,uint256,uint256,uint256,bytes,bytes)[])'));
+
+  // batchFillOrKillOrders
+  bytes4 constant batchFillOrKillOrdersSelector = 0x4d0ae546;
+  bytes4 constant batchFillOrKillOrdersSelectorGenerator = bytes4(keccak256('batchFillOrKillOrders((address,address,address,address,uint256,uint256,uint256,uint256,uint256,uint256,bytes,bytes)[],uint256[],bytes[])'));
+
+  // batchFillOrders
+  bytes4 constant batchFillOrdersSelector = 0x297bb70b;
+  bytes4 constant batchFillOrdersSelectorGenerator = bytes4(keccak256('batchFillOrders((address,address,address,address,uint256,uint256,uint256,uint256,uint256,uint256,bytes,bytes)[],uint256[],bytes[])'));
+
+  // batchFillOrdersNoThrow
+  bytes4 constant batchFillOrdersNoThrowSelector = 0x50dde190;
+  bytes4 constant batchFillOrdersNoThrowSelectorGenerator = bytes4(keccak256('batchFillOrdersNoThrow((address,address,address,address,uint256,uint256,uint256,uint256,uint256,uint256,bytes,bytes)[],uint256[],bytes[])'));
+
+  // cancelOrder
+  bytes4 constant cancelOrderSelector = 0xd46b02c3;
+  bytes4 constant cancelOrderSelectorGenerator = bytes4(keccak256('cancelOrder((address,address,address,address,uint256,uint256,uint256,uint256,uint256,uint256,bytes,bytes))'));
+
+  // cancelOrdersUpTo
+  bytes4 constant cancelOrdersUpToSelector = 0x4f9559b1;
+  bytes4 constant cancelOrdersUpToSelectorGenerator = bytes4(keccak256('cancelOrdersUpTo(uint256)'));
+
+  // cancelled
+  bytes4 constant cancelledSelector = 0x2ac12622;
+  bytes4 constant cancelledSelectorGenerator = bytes4(keccak256('cancelled(bytes32)'));
+
+  // currentContextAddress
+  bytes4 constant currentContextAddressSelector = 0xeea086ba;
+  bytes4 constant currentContextAddressSelectorGenerator = bytes4(keccak256('currentContextAddress()'));
+
+  // executeTransaction
+  bytes4 constant executeTransactionSelector = 0xbfc8bfce;
+  bytes4 constant executeTransactionSelectorGenerator = bytes4(keccak256('executeTransaction(uint256,address,bytes,bytes)'));
+
+  // fillOrKillOrder
+  bytes4 constant fillOrKillOrderSelector = 0x64a3bc15;
+  bytes4 constant fillOrKillOrderSelectorGenerator = bytes4(keccak256('fillOrKillOrder((address,address,address,address,uint256,uint256,uint256,uint256,uint256,uint256,bytes,bytes),uint256,bytes)'));
+
+  // fillOrder
+  bytes4 constant fillOrderSelector = 0xb4be83d5;
+  bytes4 constant fillOrderSelectorGenerator = bytes4(keccak256('fillOrder((address,address,address,address,uint256,uint256,uint256,uint256,uint256,uint256,bytes,bytes),uint256,bytes)'));
+
+  // fillOrderNoThrow
+  bytes4 constant fillOrderNoThrowSelector = 0x3e228bae;
+  bytes4 constant fillOrderNoThrowSelectorGenerator = bytes4(keccak256('fillOrderNoThrow((address,address,address,address,uint256,uint256,uint256,uint256,uint256,uint256,bytes,bytes),uint256,bytes)'));
+
+  // filled
+  bytes4 constant filledSelector = 0x288cdc91;
+  bytes4 constant filledSelectorGenerator = bytes4(keccak256('filled(bytes32)'));
+
+  // getAssetProxy
+  bytes4 constant getAssetProxySelector = 0x60704108;
+  bytes4 constant getAssetProxySelectorGenerator = bytes4(keccak256('getAssetProxy(bytes4)'));
+
+  // getOrderInfo
+  bytes4 constant getOrderInfoSelector = 0xc75e0a81;
+  bytes4 constant getOrderInfoSelectorGenerator = bytes4(keccak256('getOrderInfo((address,address,address,address,uint256,uint256,uint256,uint256,uint256,uint256,bytes,bytes))'));
+
+  // getOrdersInfo
+  bytes4 constant getOrdersInfoSelector = 0x7e9d74dc;
+  bytes4 constant getOrdersInfoSelectorGenerator = bytes4(keccak256('getOrdersInfo((address,address,address,address,uint256,uint256,uint256,uint256,uint256,uint256,bytes,bytes)[])'));
+
+  // isValidSignature
+  bytes4 constant isValidSignatureSelector = 0x93634702;
+  bytes4 constant isValidSignatureSelectorGenerator = bytes4(keccak256('isValidSignature(bytes32,address,bytes)'));
+
+  // marketBuyOrders
+  bytes4 constant marketBuyOrdersSelector = 0xe5fa431b;
+  bytes4 constant marketBuyOrdersSelectorGenerator = bytes4(keccak256('marketBuyOrders((address,address,address,address,uint256,uint256,uint256,uint256,uint256,uint256,bytes,bytes)[],uint256,bytes[])'));
+
+  // marketBuyOrdersNoThrow
+  bytes4 constant marketBuyOrdersNoThrowSelector = 0xa3e20380;
+  bytes4 constant marketBuyOrdersNoThrowSelectorGenerator = bytes4(keccak256('marketBuyOrdersNoThrow((address,address,address,address,uint256,uint256,uint256,uint256,uint256,uint256,bytes,bytes)[],uint256,bytes[])'));
+
+  // marketSellOrders
+  bytes4 constant marketSellOrdersSelector = 0x7e1d9808;
+  bytes4 constant marketSellOrdersSelectorGenerator = bytes4(keccak256('marketSellOrders((address,address,address,address,uint256,uint256,uint256,uint256,uint256,uint256,bytes,bytes)[],uint256,bytes[])'));
+
+  // marketSellOrdersNoThrow
+  bytes4 constant marketSellOrdersNoThrowSelector = 0xdd1c7d18;
+  bytes4 constant marketSellOrdersNoThrowSelectorGenerator = bytes4(keccak256('marketSellOrdersNoThrow((address,address,address,address,uint256,uint256,uint256,uint256,uint256,uint256,bytes,bytes)[],uint256,bytes[])'));
+
+  // matchOrders
+  bytes4 constant matchOrdersSelector = 0x3c28d861;
+  bytes4 constant matchOrdersSelectorGenerator = bytes4(keccak256('matchOrders((address,address,address,address,uint256,uint256,uint256,uint256,uint256,uint256,bytes,bytes),(address,address,address,address,uint256,uint256,uint256,uint256,uint256,uint256,bytes,bytes),bytes,bytes)'));
+
+  // orderEpoch
+  bytes4 constant orderEpochSelector = 0xd9bfa73e;
+  bytes4 constant orderEpochSelectorGenerator = bytes4(keccak256('orderEpoch(address,address)'));
+
+  // owner
+  bytes4 constant ownerSelector = 0x8da5cb5b;
+  bytes4 constant ownerSelectorGenerator = bytes4(keccak256('owner()'));
+
+  // preSign
+  bytes4 constant preSignSelector = 0x3683ef8e;
+  bytes4 constant preSignSelectorGenerator = bytes4(keccak256('preSign(bytes32,address,bytes)'));
+
+  // preSigned
+  bytes4 constant preSignedSelector = 0x82c174d0;
+  bytes4 constant preSignedSelectorGenerator = bytes4(keccak256('preSigned(bytes32,address)'));
+
+  // registerAssetProxy
+  bytes4 constant registerAssetProxySelector = 0xc585bb93;
+  bytes4 constant registerAssetProxySelectorGenerator = bytes4(keccak256('registerAssetProxy(address)'));
+
+  // setSignatureValidatorApproval
+  bytes4 constant setSignatureValidatorApprovalSelector = 0x77fcce68;
+  bytes4 constant setSignatureValidatorApprovalSelectorGenerator = bytes4(keccak256('setSignatureValidatorApproval(address,bool)'));
+
+  // transactions
+  bytes4 constant transactionsSelector = 0x642f2eaf;
+  bytes4 constant transactionsSelectorGenerator = bytes4(keccak256('transactions(bytes32)'));
+
+  // transferOwnership
+  bytes4 constant transferOwnershipSelector = 0xf2fde38b;
+  bytes4 constant transferOwnershipSelectorGenerator = bytes4(keccak256('transferOwnership(address)'));
+}
\ No newline at end of file