How I Slashed Gas Costs by 25% for a Solidity Merkle Mixer

Gas Surgery: Reducing Merkle Mixer Costs by 25% on Base Building a privacy mixer is a challenge of balance. You want strong anonymity, but you don't want the user to pay a fortune in gas for a single withdrawal. After stabilizing the Merkle Tree logic, I decided to put the contract on a strict gas diet . The results? A drop from 72,332 to 53,897 average gas. Here is how I did it. 1. The Power of Bitmaps Initially, I used a standard mapping(bytes32 => bool) to track nullifiers. Every bool in Solidity occupies a full 256-bit slot. By switching to a Bitmap implementation, we pack 256 nullifiers into a single uint256 storage slot. Bitwise operations are significantly cheaper than cold storage writes. 2. Calldata: Stop Copying Data In the first version, the Merkle Proof was passed as a memory array. This forced the EVM to copy the entire proof into memory. By switching to calldata , the contract reads the proof directly from the input, saving thousands of gas units. 3. Custom Errors Replaci