さすらいのプログラマ

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

    PUSH    EBX
    PUSH    ECX

    MOV     EAX, DWORD PTR 8[EBP]
    MOV     EAX, DWORD PTR [EAX]
    BSWAP   EAX

    MOV     ECX, EAX
    AND     ECX, 3Fh
    SHL     ECX, 8

    MOV     EBX, EAX
    AND     EBX, 3F00h
    SHL     EBX, 6
    OR      ECX, EBX

    MOV     EBX, EAX
    AND     EBX,3F0000h
    SHL     EBX, 4
    OR      ECX, EBX

    MOV     EBX, EAX
    AND     EBX, 3F000000h
    SHL     EBX, 2
    OR      ECX, EBX
    
    BSWAP   ECX

    MOV     EAX, ECX

    POP     ECX
    POP     EBX

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