さすらいのプログラマ

    TITLE    encode.asm
    .486P
.model FLAT
PUBLIC       _encode
_DATA        SEGMENT
_DATA        ENDS
_TEXT        SEGMENT
_encode      PROC NEAR
    PUSH     EBP
    MOV      EBP, ESP

    PUSH     ECX
    PUSH     EBX
    
    MOV      EAX, DWORD PTR 8[EBP]
    MOV      EAX, DWORD PTR [EAX]
    BSWAP    EAX
    SHR      EAX, 8
    
    MOV      ECX, EAX
    AND      ECX, 3Fh
    
    MOV      EBX, EAX
    AND      EBX, 0FC0h
    SHL      EBX, 2
    OR       ECX, EBX
    
    MOV      EBX, EAX
    AND      EBX, 3F000h
    SHL      EBX, 4
    OR       ECX, EBX
    
    MOV      EBX, EAX
    AND      EBX, 0FC0000h
    SHL      EBX, 6
    OR       ECX, EBX
    
    BSWAP    ECX
    MOV      EAX, ECX

    POP      EBX
    POP      ECX

    MOV      ESP, EBP
    POP      EBP
    RET      0
_encode      ENDP
_TEXT        ENDS
END