In src/mongo/db/geo/hash.cpp:

Consider making geoBitSets, bitsField, maxField, and minField const.

Consider using StringData instead of std::string or char* in initFromString, operator+, and appendHashMin to remove unnecessary calls to strlen.

Consider removing copy constructor and assignment operator, which are identical to what the compiler would produce.

Consider inlining ==, !=, getHash, and getBits.