From bec65f217fcfc1863e2989b55cfd98690dcf11ae Mon Sep 17 00:00:00 2001
From: poma <Semenov.Roman@mail.ru>
Date: Fri, 1 Nov 2019 03:54:29 +0300
Subject: [PATCH 01/18] allow fee equal to denomination

---
 contracts/Mixer.sol | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/contracts/Mixer.sol b/contracts/Mixer.sol
index 4a5b9ef..caffbcb 100644
--- a/contracts/Mixer.sol
+++ b/contracts/Mixer.sol
@@ -90,7 +90,7 @@ contract Mixer is MerkleTreeWithHistory {
     address payable relayer = address(input[3]);
     uint256 fee = input[4];
     uint256 refund = input[5];
-    require(fee < denomination, "Fee exceeds transfer value");
+    require(fee <= denomination, "Fee exceeds transfer value");
     require(!nullifierHashes[nullifierHash], "The note has been already spent");
 
     require(isKnownRoot(root), "Cannot find your merkle root"); // Make sure to use a recent one

From b578213b0c2e7b2867c1d4416bf1511b2357cdd6 Mon Sep 17 00:00:00 2001
From: poma <Semenov.Roman@mail.ru>
Date: Sat, 2 Nov 2019 11:39:07 +0300
Subject: [PATCH 02/18] check that eth value in ERC20 deposit is zero

---
 contracts/ERC20Mixer.sol | 1 +
 test/ERC20Mixer.test.js  | 8 ++++++++
 2 files changed, 9 insertions(+)

diff --git a/contracts/ERC20Mixer.sol b/contracts/ERC20Mixer.sol
index 5941f0e..fdee640 100644
--- a/contracts/ERC20Mixer.sol
+++ b/contracts/ERC20Mixer.sol
@@ -28,6 +28,7 @@ contract ERC20Mixer is Mixer {
   }
 
   function _processDeposit() internal {
+    require(msg.value == 0, "ETH value is supposed to be 0 for ETH mixer");
     safeErc20TransferFrom(msg.sender, address(this), denomination);
   }
 
diff --git a/test/ERC20Mixer.test.js b/test/ERC20Mixer.test.js
index 8e0d42d..8818a79 100644
--- a/test/ERC20Mixer.test.js
+++ b/test/ERC20Mixer.test.js
@@ -102,6 +102,14 @@ contract('ERC20Mixer', accounts => {
       logs[0].args.commitment.should.be.eq.BN(toBN(commitment))
       logs[0].args.leafIndex.should.be.eq.BN(toBN(0))
     })
+
+    it('should not allow to send ether on deposit', async () => {
+      const commitment = 43
+      await token.approve(mixer.address, tokenDenomination)
+
+      let error = await mixer.deposit(commitment, { from: sender, value: 1e6 }).should.be.rejected
+      error.reason.should.be.equal('ETH value is supposed to be 0 for ETH mixer')
+    })
   })
 
   describe('#withdraw', () => {

From 1d258715e0ccb8ac19a81bab1c0d08adaadc12d5 Mon Sep 17 00:00:00 2001
From: poma <Semenov.Roman@mail.ru>
Date: Fri, 1 Nov 2019 03:56:24 +0300
Subject: [PATCH 03/18] make operator not payable

---
 contracts/ERC20Mixer.sol | 2 +-
 contracts/ETHMixer.sol   | 2 +-
 contracts/Mixer.sol      | 6 +++---
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/contracts/ERC20Mixer.sol b/contracts/ERC20Mixer.sol
index fdee640..0a03c4d 100644
--- a/contracts/ERC20Mixer.sol
+++ b/contracts/ERC20Mixer.sol
@@ -21,7 +21,7 @@ contract ERC20Mixer is Mixer {
     uint256 _denomination,
     uint8 _merkleTreeHeight,
     uint256 _emptyElement,
-    address payable _operator,
+    address _operator,
     address _token
   ) Mixer(_verifier, _denomination, _merkleTreeHeight, _emptyElement, _operator) public {
     token = _token;
diff --git a/contracts/ETHMixer.sol b/contracts/ETHMixer.sol
index 44ebc60..b575ce5 100644
--- a/contracts/ETHMixer.sol
+++ b/contracts/ETHMixer.sol
@@ -19,7 +19,7 @@ contract ETHMixer is Mixer {
     uint256 _denomination,
     uint8 _merkleTreeHeight,
     uint256 _emptyElement,
-    address payable _operator
+    address _operator
   ) Mixer(_verifier, _denomination, _merkleTreeHeight, _emptyElement, _operator) public {
   }
 
diff --git a/contracts/Mixer.sol b/contracts/Mixer.sol
index caffbcb..619889e 100644
--- a/contracts/Mixer.sol
+++ b/contracts/Mixer.sol
@@ -28,7 +28,7 @@ contract Mixer is MerkleTreeWithHistory {
   //  - receive a relayer fee
   //  - disable new deposits in case of emergency
   //  - update snark verification key until this ability is permanently disabled
-  address payable public operator;
+  address public operator;
   bool public isDepositsEnabled = true;
   bool public isVerifierUpdateAllowed = true;
   modifier onlyOperator {
@@ -51,7 +51,7 @@ contract Mixer is MerkleTreeWithHistory {
     uint256 _denomination,
     uint8 _merkleTreeHeight,
     uint256 _emptyElement,
-    address payable _operator
+    address _operator
   ) MerkleTreeWithHistory(_merkleTreeHeight, _emptyElement) public {
     verifier = IVerifier(_verifier);
     operator = _operator;
@@ -134,7 +134,7 @@ contract Mixer is MerkleTreeWithHistory {
   }
 
   /** @dev operator can change his address */
-  function changeOperator(address payable _newAccount) external onlyOperator {
+  function changeOperator(address _newAccount) external onlyOperator {
     operator = _newAccount;
   }
 }

From b8d22464e37c6690e54ae0485f3f0aeed0574920 Mon Sep 17 00:00:00 2001
From: poma <Semenov.Roman@mail.ru>
Date: Fri, 1 Nov 2019 04:00:32 +0300
Subject: [PATCH 04/18] process deposit after changing state to prevent
 reentrancy

---
 contracts/Mixer.sol | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/contracts/Mixer.sol b/contracts/Mixer.sol
index 619889e..4f273ad 100644
--- a/contracts/Mixer.sol
+++ b/contracts/Mixer.sol
@@ -65,9 +65,9 @@ contract Mixer is MerkleTreeWithHistory {
   function deposit(uint256 commitment) public payable {
     require(isDepositsEnabled, "deposits are disabled");
     require(!commitments[commitment], "The commitment has been submitted");
-    _processDeposit();
     _insert(commitment);
     commitments[commitment] = true;
+    _processDeposit();
 
     emit Deposit(commitment, next_index - 1, block.timestamp);
   }

From 54e2c5f890cafbf0fc6f9c34195168a0b4b88109 Mon Sep 17 00:00:00 2001
From: poma <Semenov.Roman@mail.ru>
Date: Fri, 1 Nov 2019 04:07:11 +0300
Subject: [PATCH 05/18] return inserted index from merkle tree

---
 contracts/MerkleTreeWithHistory.sol | 3 ++-
 contracts/Mixer.sol                 | 4 ++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/contracts/MerkleTreeWithHistory.sol b/contracts/MerkleTreeWithHistory.sol
index 9d2f189..39145b9 100644
--- a/contracts/MerkleTreeWithHistory.sol
+++ b/contracts/MerkleTreeWithHistory.sol
@@ -56,7 +56,7 @@ contract MerkleTreeWithHistory {
     hash = R;
   }
 
-  function _insert(uint256 leaf) internal {
+  function _insert(uint256 leaf) internal returns(uint256 index) {
     uint32 current_index = next_index;
     require(current_index != 2**levels, "Merkle tree is full. No more leafs can be added");
     next_index += 1;
@@ -82,6 +82,7 @@ contract MerkleTreeWithHistory {
 
     current_root = (current_root + 1) % ROOT_HISTORY_SIZE;
     _roots[current_root] = current_level_hash;
+    return next_index - 1;
   }
 
   function isKnownRoot(uint256 root) public view returns(bool) {
diff --git a/contracts/Mixer.sol b/contracts/Mixer.sol
index 4f273ad..8da900e 100644
--- a/contracts/Mixer.sol
+++ b/contracts/Mixer.sol
@@ -65,11 +65,11 @@ contract Mixer is MerkleTreeWithHistory {
   function deposit(uint256 commitment) public payable {
     require(isDepositsEnabled, "deposits are disabled");
     require(!commitments[commitment], "The commitment has been submitted");
-    _insert(commitment);
+    uint256 insertedIndex = _insert(commitment);
     commitments[commitment] = true;
     _processDeposit();
 
-    emit Deposit(commitment, next_index - 1, block.timestamp);
+    emit Deposit(commitment, insertedIndex, block.timestamp);
   }
 
   /** @dev this function is defined in a child contract */

From d019e48da363229facaa3eaca274e0bca361354f Mon Sep 17 00:00:00 2001
From: poma <Semenov.Roman@mail.ru>
Date: Fri, 1 Nov 2019 04:11:08 +0300
Subject: [PATCH 06/18] inverted flags to reduce deploy cost, explicitly set
 state in toggleDeposits

---
 contracts/Mixer.sol   | 14 +++++++-------
 test/ETHMixer.test.js | 28 ++++++++++++++++------------
 2 files changed, 23 insertions(+), 19 deletions(-)

diff --git a/contracts/Mixer.sol b/contracts/Mixer.sol
index 8da900e..11a0ad3 100644
--- a/contracts/Mixer.sol
+++ b/contracts/Mixer.sol
@@ -29,8 +29,8 @@ contract Mixer is MerkleTreeWithHistory {
   //  - disable new deposits in case of emergency
   //  - update snark verification key until this ability is permanently disabled
   address public operator;
-  bool public isDepositsEnabled = true;
-  bool public isVerifierUpdateAllowed = true;
+  bool public isDepositsDisabled;
+  bool public isVerifierUpdateDisabled;
   modifier onlyOperator {
     require(msg.sender == operator, "Only operator can call this function.");
     _;
@@ -63,7 +63,7 @@ contract Mixer is MerkleTreeWithHistory {
     @param commitment the note commitment, which is PedersenHash(nullifier + secret)
   */
   function deposit(uint256 commitment) public payable {
-    require(isDepositsEnabled, "deposits are disabled");
+    require(!isDepositsDisabled, "deposits are disabled");
     require(!commitments[commitment], "The commitment has been submitted");
     uint256 insertedIndex = _insert(commitment);
     commitments[commitment] = true;
@@ -112,8 +112,8 @@ contract Mixer is MerkleTreeWithHistory {
     @dev Allow operator to temporarily disable new deposits. This is needed to protect users funds in case a vulnerability is discovered.
     It does not affect existing deposits.
   */
-  function toggleDeposits() external onlyOperator {
-    isDepositsEnabled = !isDepositsEnabled;
+  function toggleDeposits(bool _state) external onlyOperator {
+    isDepositsDisabled = _state;
   }
 
   /**
@@ -121,7 +121,7 @@ contract Mixer is MerkleTreeWithHistory {
     After that operator is supposed to permanently disable this ability.
   */
   function updateVerifier(address newVerifier) external onlyOperator {
-    require(isVerifierUpdateAllowed, "Verifier updates have been disabled.");
+    require(!isVerifierUpdateDisabled, "Verifier updates have been disabled.");
     verifier = IVerifier(newVerifier);
   }
 
@@ -130,7 +130,7 @@ contract Mixer is MerkleTreeWithHistory {
     This is supposed to be called after the final trusted setup ceremony is held.
   */
   function disableVerifierUpdate() external onlyOperator {
-    isVerifierUpdateAllowed = false;
+    isVerifierUpdateDisabled = true;
   }
 
   /** @dev operator can change his address */
diff --git a/test/ETHMixer.test.js b/test/ETHMixer.test.js
index 2462b23..b1c00f2 100644
--- a/test/ETHMixer.test.js
+++ b/test/ETHMixer.test.js
@@ -115,11 +115,15 @@ contract('ETHMixer', accounts => {
 
     it('should not deposit if disabled', async () => {
       let commitment = 42;
-      (await mixer.isDepositsEnabled()).should.be.equal(true)
-      const err = await mixer.toggleDeposits({ from: accounts[1] }).should.be.rejected
+      (await mixer.isDepositsDisabled()).should.be.equal(false)
+      const err = await mixer.toggleDeposits(true, { from: accounts[1] }).should.be.rejected
       err.reason.should.be.equal('Only operator can call this function.')
-      await mixer.toggleDeposits({ from: sender });
-      (await mixer.isDepositsEnabled()).should.be.equal(false)
+      await mixer.toggleDeposits(false, { from: sender });
+      (await mixer.isDepositsDisabled()).should.be.equal(false)
+      await mixer.toggleDeposits(true, { from: sender });
+      (await mixer.isDepositsDisabled()).should.be.equal(true)
+      await mixer.toggleDeposits(true, { from: sender });
+      (await mixer.isDepositsDisabled()).should.be.equal(true)
       let error = await mixer.deposit(commitment, { value, from: sender }).should.be.rejected
       error.reason.should.be.equal('deposits are disabled')
     })
@@ -484,26 +488,26 @@ contract('ETHMixer', accounts => {
       let operator = await mixer.operator()
       operator.should.be.equal(sender)
 
-      let isVerifierUpdateAllowed = await mixer.isVerifierUpdateAllowed()
-      isVerifierUpdateAllowed.should.be.equal(true)
+      let isVerifierUpdateDisabled = await mixer.isVerifierUpdateDisabled()
+      isVerifierUpdateDisabled.should.be.equal(false)
 
       await mixer.disableVerifierUpdate().should.be.fulfilled
 
-      const newValue = await mixer.isVerifierUpdateAllowed()
-      newValue.should.be.equal(false)
+      const newValue = await mixer.isVerifierUpdateDisabled()
+      newValue.should.be.equal(true)
     })
 
     it('cannot update verifier after this function is called', async () => {
       let operator = await mixer.operator()
       operator.should.be.equal(sender)
 
-      let isVerifierUpdateAllowed = await mixer.isVerifierUpdateAllowed()
-      isVerifierUpdateAllowed.should.be.equal(true)
+      let isVerifierUpdateDisabled = await mixer.isVerifierUpdateDisabled()
+      isVerifierUpdateDisabled.should.be.equal(false)
 
       await mixer.disableVerifierUpdate().should.be.fulfilled
 
-      const newValue = await mixer.isVerifierUpdateAllowed()
-      newValue.should.be.equal(false)
+      const newValue = await mixer.isVerifierUpdateDisabled()
+      newValue.should.be.equal(true)
 
       const newVerifier = accounts[7]
       const error = await mixer.updateVerifier(newVerifier).should.be.rejected

From 02e76a1ce6b44958e050cdb9cd755d1dba6ce475 Mon Sep 17 00:00:00 2001
From: poma <Semenov.Roman@mail.ru>
Date: Fri, 1 Nov 2019 04:14:01 +0300
Subject: [PATCH 07/18] pass verifier address as IVerifier

---
 contracts/ERC20Mixer.sol | 2 +-
 contracts/ETHMixer.sol   | 2 +-
 contracts/Mixer.sol      | 4 ++--
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/contracts/ERC20Mixer.sol b/contracts/ERC20Mixer.sol
index 0a03c4d..a7c6c58 100644
--- a/contracts/ERC20Mixer.sol
+++ b/contracts/ERC20Mixer.sol
@@ -17,7 +17,7 @@ contract ERC20Mixer is Mixer {
   address public token;
 
   constructor(
-    address _verifier,
+    IVerifier _verifier,
     uint256 _denomination,
     uint8 _merkleTreeHeight,
     uint256 _emptyElement,
diff --git a/contracts/ETHMixer.sol b/contracts/ETHMixer.sol
index b575ce5..56a9aed 100644
--- a/contracts/ETHMixer.sol
+++ b/contracts/ETHMixer.sol
@@ -15,7 +15,7 @@ import "./Mixer.sol";
 
 contract ETHMixer is Mixer {
   constructor(
-    address _verifier,
+    IVerifier _verifier,
     uint256 _denomination,
     uint8 _merkleTreeHeight,
     uint256 _emptyElement,
diff --git a/contracts/Mixer.sol b/contracts/Mixer.sol
index 11a0ad3..b16383c 100644
--- a/contracts/Mixer.sol
+++ b/contracts/Mixer.sol
@@ -47,13 +47,13 @@ contract Mixer is MerkleTreeWithHistory {
     @param _operator operator address (see operator above)
   */
   constructor(
-    address _verifier,
+    IVerifier _verifier,
     uint256 _denomination,
     uint8 _merkleTreeHeight,
     uint256 _emptyElement,
     address _operator
   ) MerkleTreeWithHistory(_merkleTreeHeight, _emptyElement) public {
-    verifier = IVerifier(_verifier);
+    verifier = _verifier;
     operator = _operator;
     denomination = _denomination;
   }

From 111c966c1eb256a97998069d99c7ac9ff94283ac Mon Sep 17 00:00:00 2001
From: poma <Semenov.Roman@mail.ru>
Date: Fri, 1 Nov 2019 04:15:55 +0300
Subject: [PATCH 08/18] add assert on denomination

---
 contracts/Mixer.sol | 1 +
 1 file changed, 1 insertion(+)

diff --git a/contracts/Mixer.sol b/contracts/Mixer.sol
index b16383c..d21e85d 100644
--- a/contracts/Mixer.sol
+++ b/contracts/Mixer.sol
@@ -53,6 +53,7 @@ contract Mixer is MerkleTreeWithHistory {
     uint256 _emptyElement,
     address _operator
   ) MerkleTreeWithHistory(_merkleTreeHeight, _emptyElement) public {
+    require(_denomination > 0, "denomination should be greater than 0");
     verifier = _verifier;
     operator = _operator;
     denomination = _denomination;

From 8e8243823a2939226e91f4f40c376cbbdd58f150 Mon Sep 17 00:00:00 2001
From: poma <Semenov.Roman@mail.ru>
Date: Fri, 1 Nov 2019 04:17:00 +0300
Subject: [PATCH 09/18] make inheritable functions abstract

---
 contracts/Mixer.sol | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/contracts/Mixer.sol b/contracts/Mixer.sol
index d21e85d..760564c 100644
--- a/contracts/Mixer.sol
+++ b/contracts/Mixer.sol
@@ -74,7 +74,7 @@ contract Mixer is MerkleTreeWithHistory {
   }
 
   /** @dev this function is defined in a child contract */
-  function _processDeposit() internal {}
+  function _processDeposit() internal;
 
   /**
     @dev Withdraw deposit from the mixer. `proof` is a zkSNARK proof data, and input is an array of circuit public inputs
@@ -102,7 +102,7 @@ contract Mixer is MerkleTreeWithHistory {
   }
 
   /** @dev this function is defined in a child contract */
-  function _processWithdraw(address payable _receiver, address payable _relayer, uint256 _fee, uint256 _refund) internal {}
+  function _processWithdraw(address payable _receiver, address payable _relayer, uint256 _fee, uint256 _refund) internal;
 
   /** @dev whether a note is already spent */
   function isSpent(uint256 nullifier) public view returns(bool) {

From 35500ac5bb83c0bff0a23e22001f4ac781c9ab6c Mon Sep 17 00:00:00 2001
From: poma <Semenov.Roman@mail.ru>
Date: Sat, 2 Nov 2019 13:09:02 +0300
Subject: [PATCH 10/18] change arg name

---
 contracts/Mixer.sol | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/contracts/Mixer.sol b/contracts/Mixer.sol
index 760564c..310432f 100644
--- a/contracts/Mixer.sol
+++ b/contracts/Mixer.sol
@@ -105,8 +105,8 @@ contract Mixer is MerkleTreeWithHistory {
   function _processWithdraw(address payable _receiver, address payable _relayer, uint256 _fee, uint256 _refund) internal;
 
   /** @dev whether a note is already spent */
-  function isSpent(uint256 nullifier) public view returns(bool) {
-    return nullifierHashes[nullifier];
+  function isSpent(uint256 nullifierHash) public view returns(bool) {
+    return nullifierHashes[nullifierHash];
   }
 
   /**

From 48cc57fad7f0f18ae98e5f47054f335f0c9c33f8 Mon Sep 17 00:00:00 2001
From: poma <Semenov.Roman@mail.ru>
Date: Fri, 1 Nov 2019 04:28:46 +0300
Subject: [PATCH 11/18] change arg name

---
 contracts/Mixer.sol | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/contracts/Mixer.sol b/contracts/Mixer.sol
index 310432f..1fd9466 100644
--- a/contracts/Mixer.sol
+++ b/contracts/Mixer.sol
@@ -135,7 +135,7 @@ contract Mixer is MerkleTreeWithHistory {
   }
 
   /** @dev operator can change his address */
-  function changeOperator(address _newAccount) external onlyOperator {
-    operator = _newAccount;
+  function changeOperator(address _newOperator) external onlyOperator {
+    operator = _newOperator;
   }
 }

From 2bb751bfd173686c0f8b6d55b01d1570c7851198 Mon Sep 17 00:00:00 2001
From: poma <Semenov.Roman@mail.ru>
Date: Fri, 1 Nov 2019 04:30:07 +0300
Subject: [PATCH 12/18] change ROOT_HISTORY_SIZE type

---
 contracts/MerkleTreeWithHistory.sol | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/contracts/MerkleTreeWithHistory.sol b/contracts/MerkleTreeWithHistory.sol
index 39145b9..6fc6b3a 100644
--- a/contracts/MerkleTreeWithHistory.sol
+++ b/contracts/MerkleTreeWithHistory.sol
@@ -18,7 +18,7 @@ library Hasher {
 contract MerkleTreeWithHistory {
   uint256 public levels;
 
-  uint8 constant ROOT_HISTORY_SIZE = 100;
+  uint256 constant ROOT_HISTORY_SIZE = 100;
   uint256[] private _roots;
   uint256 public current_root = 0;
 

From 1364762b930eca00cbee7d6307fcb73466780969 Mon Sep 17 00:00:00 2001
From: poma <Semenov.Roman@mail.ru>
Date: Fri, 1 Nov 2019 04:31:57 +0300
Subject: [PATCH 13/18] make _roots constant sized array

---
 contracts/MerkleTreeWithHistory.sol | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/contracts/MerkleTreeWithHistory.sol b/contracts/MerkleTreeWithHistory.sol
index 6fc6b3a..3ff3b0b 100644
--- a/contracts/MerkleTreeWithHistory.sol
+++ b/contracts/MerkleTreeWithHistory.sol
@@ -19,7 +19,7 @@ contract MerkleTreeWithHistory {
   uint256 public levels;
 
   uint256 constant ROOT_HISTORY_SIZE = 100;
-  uint256[] private _roots;
+  uint256[ROOT_HISTORY_SIZE] private _roots;
   uint256 public current_root = 0;
 
   uint256[] private _filled_subtrees;
@@ -38,7 +38,6 @@ contract MerkleTreeWithHistory {
       _filled_subtrees.push(_zeros[i]);
     }
 
-    _roots = new uint256[](ROOT_HISTORY_SIZE);
     _roots[0] = hashLeftRight(_zeros[levels - 1], _zeros[levels - 1]);
   }
 
@@ -122,7 +121,7 @@ contract MerkleTreeWithHistory {
     return _roots[current_root];
   }
 
-  function roots() public view returns(uint256[] memory) {
+  function roots() public view returns(uint256[ROOT_HISTORY_SIZE] memory) {
     return _roots;
   }
 

From 6571f54768cdf3b44f90a0bdce63dbff2d7a6b25 Mon Sep 17 00:00:00 2001
From: poma <Semenov.Roman@mail.ru>
Date: Fri, 1 Nov 2019 04:32:26 +0300
Subject: [PATCH 14/18] make _roots public

---
 contracts/MerkleTreeWithHistory.sol | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/contracts/MerkleTreeWithHistory.sol b/contracts/MerkleTreeWithHistory.sol
index 3ff3b0b..8917fda 100644
--- a/contracts/MerkleTreeWithHistory.sol
+++ b/contracts/MerkleTreeWithHistory.sol
@@ -19,7 +19,7 @@ contract MerkleTreeWithHistory {
   uint256 public levels;
 
   uint256 constant ROOT_HISTORY_SIZE = 100;
-  uint256[ROOT_HISTORY_SIZE] private _roots;
+  uint256[ROOT_HISTORY_SIZE] public _roots;
   uint256 public current_root = 0;
 
   uint256[] private _filled_subtrees;

From 609510654975487dcaf9be4dbe3588bd6f9f8534 Mon Sep 17 00:00:00 2001
From: poma <Semenov.Roman@mail.ru>
Date: Fri, 1 Nov 2019 04:33:02 +0300
Subject: [PATCH 15/18] rename current root index

---
 contracts/MerkleTreeWithHistory.sol | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/contracts/MerkleTreeWithHistory.sol b/contracts/MerkleTreeWithHistory.sol
index 8917fda..f294719 100644
--- a/contracts/MerkleTreeWithHistory.sol
+++ b/contracts/MerkleTreeWithHistory.sol
@@ -20,7 +20,7 @@ contract MerkleTreeWithHistory {
 
   uint256 constant ROOT_HISTORY_SIZE = 100;
   uint256[ROOT_HISTORY_SIZE] public _roots;
-  uint256 public current_root = 0;
+  uint256 public current_root_index = 0;
 
   uint256[] private _filled_subtrees;
   uint256[] private _zeros;
@@ -79,8 +79,8 @@ contract MerkleTreeWithHistory {
       current_index /= 2;
     }
 
-    current_root = (current_root + 1) % ROOT_HISTORY_SIZE;
-    _roots[current_root] = current_level_hash;
+    current_root_index = (current_root_index + 1) % ROOT_HISTORY_SIZE;
+    _roots[current_root_index] = current_level_hash;
     return next_index - 1;
   }
 
@@ -90,14 +90,14 @@ contract MerkleTreeWithHistory {
     }
     // search most recent first
     uint256 i;
-    for(i = current_root; i < 2**256 - 1; i--) {
+    for(i = current_root_index; i < 2**256 - 1; i--) {
       if (root == _roots[i]) {
         return true;
       }
     }
 
     // process the rest of roots
-    for(i = ROOT_HISTORY_SIZE - 1; i > current_root; i--) {
+    for(i = ROOT_HISTORY_SIZE - 1; i > current_root_index; i--) {
       if (root == _roots[i]) {
         return true;
       }
@@ -118,7 +118,7 @@ contract MerkleTreeWithHistory {
   }
 
   function getLastRoot() public view returns(uint256) {
-    return _roots[current_root];
+    return _roots[current_root_index];
   }
 
   function roots() public view returns(uint256[ROOT_HISTORY_SIZE] memory) {

From c47408ebd703bb68491c5d0db0b6bdef27c944cc Mon Sep 17 00:00:00 2001
From: poma <Semenov.Roman@mail.ru>
Date: Sat, 2 Nov 2019 14:29:43 +0300
Subject: [PATCH 16/18] cache current_zero value to prevent excessive SLOADs

---
 contracts/MerkleTreeWithHistory.sol | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/contracts/MerkleTreeWithHistory.sol b/contracts/MerkleTreeWithHistory.sol
index f294719..8a6b705 100644
--- a/contracts/MerkleTreeWithHistory.sol
+++ b/contracts/MerkleTreeWithHistory.sol
@@ -28,17 +28,20 @@ contract MerkleTreeWithHistory {
   uint32 public next_index = 0;
 
   constructor(uint256 tree_levels, uint256 zero_value) public {
+    require(tree_levels > 0, "tree_levels should be greater than zero");
     levels = tree_levels;
 
+    uint256 current_zero = zero_value;
     _zeros.push(zero_value);
-    _filled_subtrees.push(_zeros[0]);
+    _filled_subtrees.push(current_zero);
 
     for (uint8 i = 1; i < levels; i++) {
-      _zeros.push(hashLeftRight(_zeros[i-1], _zeros[i-1]));
-      _filled_subtrees.push(_zeros[i]);
+      current_zero = hashLeftRight(current_zero, current_zero);
+      _zeros.push(current_zero);
+      _filled_subtrees.push(current_zero);
     }
 
-    _roots[0] = hashLeftRight(_zeros[levels - 1], _zeros[levels - 1]);
+    _roots[0] = hashLeftRight(current_zero, current_zero);
   }
 
   function hashLeftRight(uint256 left, uint256 right) public pure returns (uint256 hash) {

From 91adb03131a986da19a976960e8094ed6535b214 Mon Sep 17 00:00:00 2001
From: poma <Semenov.Roman@mail.ru>
Date: Sat, 2 Nov 2019 11:12:11 +0300
Subject: [PATCH 17/18] add solidity version to IUSDT

---
 contracts/Mocks/IUSDT.sol | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/contracts/Mocks/IUSDT.sol b/contracts/Mocks/IUSDT.sol
index 8bd9ead..4425677 100644
--- a/contracts/Mocks/IUSDT.sol
+++ b/contracts/Mocks/IUSDT.sol
@@ -1,3 +1,5 @@
+pragma solidity ^0.5.8;
+
 contract ERC20Basic {
     uint public _totalSupply;
     function totalSupply() public view returns (uint);

From c92ac97ff277d5b3fa0f5aca2cae20fd41d1bae3 Mon Sep 17 00:00:00 2001
From: poma <Semenov.Roman@mail.ru>
Date: Sat, 2 Nov 2019 13:19:06 +0300
Subject: [PATCH 18/18] make field_size constant, return extra addmod, refactor
 return

---
 contracts/MerkleTreeWithHistory.sol | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/contracts/MerkleTreeWithHistory.sol b/contracts/MerkleTreeWithHistory.sol
index 8a6b705..0deb5a7 100644
--- a/contracts/MerkleTreeWithHistory.sol
+++ b/contracts/MerkleTreeWithHistory.sol
@@ -18,6 +18,7 @@ library Hasher {
 contract MerkleTreeWithHistory {
   uint256 public levels;
 
+  uint256 constant FIELD_SIZE = 21888242871839275222246405745257275088548364400416034343698204186575808495617;
   uint256 constant ROOT_HISTORY_SIZE = 100;
   uint256[ROOT_HISTORY_SIZE] public _roots;
   uint256 public current_root_index = 0;
@@ -45,17 +46,15 @@ contract MerkleTreeWithHistory {
   }
 
   function hashLeftRight(uint256 left, uint256 right) public pure returns (uint256 hash) {
-    uint256 k = 21888242871839275222246405745257275088548364400416034343698204186575808495617;
-    uint256 R = 0;
+    uint256 R = left; // left is already checked to be less than field_size by snark verifier
     uint256 C = 0;
 
-    R = addmod(R, left, k);
     (R, C) = Hasher.MiMCSponge(R, C, 0);
 
-    R = addmod(R, right, k);
+    R = addmod(R, right, FIELD_SIZE);
     (R, C) = Hasher.MiMCSponge(R, C, 0);
 
-    hash = R;
+    return R;
   }
 
   function _insert(uint256 leaf) internal returns(uint256 index) {