# Quant Exchange - Halborn Report Response ### (HAL-01) Floating Pragma All the relevant contracts are now fixed to a 0.5.17 version pragma: [3cbe3ad ](https://github.com/Quant-Finance-HQ/0x-monorepo/commit/3cbe3adc8e2e13ef731f569813b59ff30d8b369c). ### (HAL-02) Experimental Features Enabled As the bug report article states ["The 0.5.7 release contains the fixes to all bugs explained in this blog post"](https://blog.ethereum.org/2019/03/26/solidity-optimizer-and-abiencoderv2-bug/), and we're now using a fixed 0.5.17 solidity version, which includes fixes for the bug in question. ### (HAL-03) Gas Optimization on the Divide Ceil Calculation We implemented the recommended gas optimization on commit [251440b](https://github.com/Quant-Finance-HQ/0x-monorepo/commit/251440b622a9b500df97ad98a44dedda0ebc047b). ### (HAL-04) Lack of Integer Underflow Protection The missing integer underlow protection on `MixinProtocolFees` was added on commit [bb4257a](https://github.com/Quant-Finance-HQ/0x-monorepo/commit/bb4257a25495c9ce19f7dcfeb64bb62cfff3b7ec). ### (HAL-05) Lack of Zero Address Check Missing zero address checks added on commit [9037c9f](https://github.com/Quant-Finance-HQ/0x-monorepo/commit/9037c9fbf1289fc73164410b3303900f339704ec). ### (HAL-06) Usage of assert The assert clause in `MixinSignatureValidator` is justified because if the internal `_validateHashSignatureTypes` function were called with an invalid signature type, that would classify as an internal error. The assert on `MixinWrapperFunctions` also checks for an internal error on the return data length for a `delegatecall` to the Exchange contract itself (which inherits from MixinWrapperFunctions). ### (HAL-07) Missing Event Emitting Missing events on the OrderChecker contract were added on commit [a9c92db](https://github.com/Quant-Finance-HQ/0x-monorepo/commit/a9c92dbc5b79e9dad440946ac9ea1175329876ec). ### (HAL-08) Lack of Oracle Return Value Check The missing return value check was added on commit [e6f34aa](https://github.com/Quant-Finance-HQ/0x-monorepo/commit/e6f34aa2cdaaf80dd58ecdd8fcfacd0f2fceca6d). ### (HAL-09) Lack of Oracle Status Check When calculating fees, the status of the oracle for the underlying asset in question is now checked and it needs to be active: [2fdb31f](https://github.com/Quant-Finance-HQ/0x-monorepo/commit/2fdb31fc93b31d0cb3983ba4648a05b6afd261f3).