Homebrew Need help with checksum8

[dj_skual]

hello

i'm trying to make downloaded miis editable.

i read in libmii and on wiibrew that the mii is linked with the wii by the mac address.

Inside the mii structure, there are 4 values.
SystemID0: checksum8 of first 3 bytes of wii mac address
SystemID1: 4th byte of wii mac address
SystemID2: 5th byte of wii mac address
SystemID3: 6th byte of wii mac address

also, i read my wii mac address: no problem with ID1, ID2, and ID3, they match with my mac address.
problem is with ID0.
my first 3 bytes of mac address are 0x8c, 0x56, 0xc5.
the ID0 stored in all miis created with my wii is 0x27.

the problem is i can't find the way to find this result with my mac address.

if someone have an idea...
please, need help, i'm going crazy