Multihash uses base128 varints (variable length ints) for codes and lengths >= 128. While not all implementations need to support varints, an implementation that doesn't should check that the length/code is less than 128 and return a "not supported" error otherwise.
https://github.com/cpp-ipfs/cpp-multihash/blob/875d95b2acbef72286910efd4f71c7ec1e3b8c6c/multihash/detail/HashRawCodecImpl.cpp#L8
Multihash uses base128 varints (variable length ints) for codes and lengths >= 128. While not all implementations need to support varints, an implementation that doesn't should check that the length/code is less than 128 and return a "not supported" error otherwise.