IBM MOD 11 Algorithm

Post a clever/fast/short implementation of this algorithm

http://en.wikipedia.org/wiki/MSI_Barcode#Mod_11_Check_Digit (IBM version)

¡In any programming language you want!

Skill level: 1 of 10

INB4: Check my Anus


    ; in: si pointing to reversed digit string
    ;     cx length of digit string
    ; out: al = check digit
    xor ax, ax
calcloop:
    lodsb
    xchg al, ah
aadpos equ $+1
    aad 2
    inc byte [aadpos]
    cmp byte [aadpos], 7
    jbe noreset
    mov byte [aadpos], 2
noreset:
    xchg al, ah
    loop calcloop
    mov al, ah
    aam 11
    neg al
    add al, 11
    aam 11
37 bytes. Anyone want to go for shorter?