CMSI 284 Preparation for the Final
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To prepare, take this exam. See if you can finish in two hours.

1.  Convert the following UTF-32 encoded codepoints to UTF-8
    (Express your answer in hex):

    000369F5  ____________________________

    0000E09A  ____________________________

    00000080  ____________________________



2.  Give the single precision IEEE-754 encoding of 514.625
    and explain your answer.

3.  Give x86 logic operations to perform the following operations
    on the esi register (assuming that it contains an unsigned number).

    Complement the two highest order bits  ___________________________________


    Replace it with its value mod 64  _______________________________________

    Replace it with the largest multiple
    of 8 less than or equal to itself  ______________________________________


4.  Explain in great detail why the decoding of
    the IA-32 machine instruction F0F30F1414C581FFFFFF
    is lock repe unpcklps xmm2, [8*eax-127]

5.  Write a C function that takes in a string <i>s</i> and an
    int <i>k</i> and returns a newly allocated string containing
    <i>s<sup>k</sup></i>.  In case you haven't seen that notation
    before, here's an example: <tt>ho<sup>3</sup> = hohoho</tt>.
    A hint you shouldn't need: Use malloc, strcpy and strcat... or
    strncpy and strncat if you can't stand the sight of the n-less
    versions.  Hint: Be very careful about the '\0' at the end.


6.  Write, in assembly language, a function to exchange each
    of the characters at even numbered positions (the first position is 0)
    with their successors, that is intended to be called from C.  The
    function should turn "abcdefghij" into "badcfehgji".  Actually
    swap the characters in the string; don't return a new string.

7.  Write a standalone program, using Linux system calls and
    no external libraries at all, that applies the Caesar cipher with
    a key of 3 to standard input writing the ciphertext to standard
    output. Reading is done with system call 3, which accepts, in order
    the following parameters: the file handle, the address of the buffer
    to read into, and the number of bytes to read.  It returns the
    number of bytes actually read. The file handle
    for standard input is 0.  You already know about the write system
    call.  (See the web for the definition of Caesar cipher).


8.  I wrote a program and saw that the machine code in the
    object file was <tt>31 DB 43 89 D8 C1 E0 01 89 C2 C1 E0 01 B9 16 00
    00 00 CD 80 EB EA 79 0A</tt>.  When it was loaded into memory, however,
    I noticed it was <tt>31 DB 43 89 D8 C1 E0 01 89 C2 C1 E0 01 B9 8A 80
    04 08 CD 80 EB EA 79 0A</tt>.  Explain the difference. What memory
    location was the program loaded at?  For extra credit, what
    program is this?

9.  What is the intent of this following function?

    mystery:  call    helper
              ret
    helper:   mov     eax, [esp]
              sub     eax, 5
              ret

    Note that superficial, obvious observations like "it calls a function
    that returns 5 less than the value on the stack top" will earn you zero
    points.  Tell me intent of the code, then tell me a much simpler way to do that.