Conditional Execution

Tom Kelliher, CS 240

Sept. 9, 2005

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Assignment

None.

From Last Time

Logical and branch instructions.

Outline

  1. Compiling HLL control structures.

  2. Class teamwork assignment.

Coming Up

Intro to Linux.

Compiling HLL Control Structures

Write MIPS code fragments corresponding to the following:

  1. Compiling an if:

    \begin{figure}\centering\includegraphics[]{Figures/if.eps}\end{figure} 

    if (i < 12)
   ++i;
else
   --j;

  2. Compiling a loop:

    \begin{figure}\centering\includegraphics[]{Figures/loop.eps}\end{figure} 

    i = 1;
j = 0;
while (i < 200)
{
   j += i;
   i *= i;
}

Class Teamwork Assignment

The class, working as a team, is to e-mail the solution to the following problems to me (I'll collect the solutions and e-mail them as one to the class.) Let me know who participated in the solution of what problem(s). 

  1. j = 0;
for (i = 0; i < 10; ++i)
   j += i;


  2. j = 0;
for (i = 0; i < 10; ++i)
   if (i > 5)
      j += i;


  3. while (i > 0 && i < 10)
   ++i;


  4. if (i < 12 && j > 3 || k != 0)
   ++i;
else if (i == 33)
   --j;
else
   k += 2;

  5. (3.9 from the text) The naive way of compiling 
    while (save[i] == k)
   i += k;
    requires execution of both a conditional branch and an unconditional jump each time through the loop. Produce the naive code.

    Optimize the naive code so that only a conditional branch is executed each time through the loop.

  6. (3.24 from the text, a variation) Write a code segment which takes two ``parameters:''
    1. An ASCII character in $a0.

    2. A pointer to a NULL-terminated string in $a1.

    and ``returns'' a count of the number of occurrences of the character in the string in $v0.


Thomas P. Kelliher 2005-09-07
Tom Kelliher