CS/COE 447 Homework 2  Due Wednesday February 21, 2007
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PLEASE BE SURE TO INCLUDE YOUR NAME ON YOUR ANSWERS.

Please submit directly to the grader's mailbox:

       Grader: Michel Hanna - 6th floor mail room, SENNOTT SQUARE

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(1)[10pts]   Exercise 2.6

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(2).A[5pts] (based on Exercise 2.14)

The MIPS translation of the C segment

  while (save[i] == k)
      i += 1;

on page 74 executes both a conditional branch instruction and an
unconditional jump instruction each time through the loop. Only poor
compilers would produce code with this loop overhead.  Rewrite the
assembly code so that it uses at most one branch or jump each time
through the loop. **Don't make any other changes to the code.**

Assuming the number of iterations of the loop is 10, how many
instructions are executed by the original version, and how many
instructions are executed by your new version?

Assume: 
  $s3 -- i
  $s5 -- k
  $s6 -- base address of the array

Original Code:

loop: sll $t1,$s3,2
      add $t1,$t1,$s6
      lw $t0,0($t1)
      bne $t0,$s5,exit
      addi $s3,$s3,1
      j loop
exit:

(2).B[5pts] 
Make your code even more efficient, by initializing $t1 to the address
of array[i] before the loop, and then replacing the first two
instructions of the loop by one instruction.    How many total
instructions are executed (including your new initialization),
assuming that the number of iterations of the loop is 10?

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(3)[10pts] Exercise 2.30

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(4)[10pts] Exercise 2.31

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(5)[10pts] Exercise 2.37

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(6)[30pts] Exercises 3.1,3.2,3.3,3.4,3.5,3.6

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(7)[10pts] Exercise 3.7  Include comments explaining how your code
segment accomplishes the task.  Your comments should show you
understand your solution.

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(8)[10pts] Exercise 3.10  Note that this method can be used to detect
unsigned overflow.

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