Function new_m57 

pub fn new_m57(
    prg_rom: Box<[u8]>,
    chr_rom: Box<[u8]>,
    mirroring: Mirroring,
) -> Result<DiscreteMapper, MapperError>

Mapper 57 (BMC GK 6-in-1 multicart).

Errors

MapperError::Invalid on a bad PRG/CHR size.