Gas: Shift Right instead of Dividing by 2

[code423n4]

Handle

Dravee

Vulnerability details

Impact

A division by 2 can be calculated by shifting one to the right.

While the DIV opcode uses 5 gas, the SHR opcode only uses 3 gas. Furthermore, Solidity's division operation also includes a division-by-0 prevention which is bypassed using shifting.

POC

Instances include:

contracts\XOLE.sol:230:            uint center = upper - (upper - lower) / 2;
contracts\XOLE.sol:418:            uint32 center = upper - (upper - lower) / 2;

Tools Used

VS Code

Recommended Mitigation Steps

Replace / 2 with >> 1