ASSIGNMENT 4 Solution

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In this assignment you will optimize code and get it to run faster using

techniques you have learned in this course.




You will measure code execution time using the Linux time(1) command. This

command prints out three numbers:




real: total elapsed time

user: total cpu usage of the application code

sys: total cpu usage of the application's operating system calls




For the purposes of this assignment, you will use the user statistic returned by

time(1).




You should do this work on syccuxas01.pcc.edu. This is where I will be testing

your code, and execution times on this machine are the standard that your code

will be judged by. The fact that your code may have met the timing standard on

some other machine does not count, and will not help you.




The code for this assignment has an outer loop and an inner loop. The inner loop

computes the sum of the numbers in an array (note that the array is initialized

by calloc() to all zeroes). The outer loop repeats the inner loop's computation

the specified number of times. You should maintain this loop structure as you

optimize this code. In particular:




* you should not alter the outer loop

* you should not change the size of the array or its data type

* the array should remain initialized to all zeroes -

do not change any element of the array

* your inner loop should still compute the sum of all the elements

of the array

* your code should be no longer than 100 lines

* your code should not use the "register" keyword




The basic idea is to change the contents of the inner loop to make the

computation run faster while having it still repeatedly compute the sum of the

array elements.




Do not write any assembly language for this assignment. You can achieve the

speedup you need at the C code level.




Do not use the 'register' keyword. There's a good chance it will produce strange,

irrelevant, and completely wrong results for you. You can accomplish everything

you need to without using it.




Do not use the optimization features of gcc. I will be compiling your code with

all gcc optimizations turned off. Compile your code with same flags that are

used by the 'gc' bash script in ~michael.trigoboff/bin.




The "Loop Optimization" section of the "Optimizing Code" page of the

"Optimization" lesson demonstrates techniques that may be of use to you for this

assignment. There are code examples of the techniques in




~michael.trigoboff/cs201/code/optimize/loopOptimization




Remember that you need to do only one of the versions below.




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REGULAR VERSION




Optimize the code in a04.c so that it runs in less than 7.0 seconds.




Upload your work as file a04.c.




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PREMIUM VERSION




Optimize the code in a04.c so that it runs in less than 5.0 seconds.




Upload your work as file a04.c.




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REQUIRED PLATFORM




I grade your code on syccuxas01.pcc.edu. Your code is required to compile and

run correctly on that machine.




COMPILING YOUR CODE




You are required to compile your code with the same flags that are used by

the 'gc' bash script in ~michael.trigoboff/bin.




GRADING YOUR CODE




Your code needs to compile without errors or warnings and run correctly. Code

that does not compile will receive zero points. Code that crashes will receive

zero points.




I use bash scripts to grade your code. Because of this, it is very important

that you submit your code with the file name that was requested. If you change

the file name, my scripts will crash, your work will not be graded, you will

have to resubmit a corrected version of your work, and you will lose points.




My scripts produce a log file containing your code, compiler warnings and errors

(if any), your code's output, and some statistics that are useful to me. I then

personally go through that log file to produce your grade. In other words, the

scripts don't generate your grade, they just make it more convenient for me to

generate your grade.




TO SUBMIT THIS ASSIGNMENT




Submit the requested file to Desire2Learn.




* Be certain to check that you completed the upload successfully. After you

click the Upload File button, you must also click the SUBMIT ASSIGNMENT

button. This is very easy to forget. If you do not do this, I will not

see your work and you will get a grade of zero for the assignment. I

would recommend entering an email address so you can be notified that

the upload was completed successfully.

* You may upload as many versions as you wish prior to the due date. I will

only see and grade the final one. You will not be able to upload

assignments after the due date.




Points will be deducted for uploading a file with a name that is not as

specified. Every term I get a few students whose approach to following

directions is, shall we say, "creative." I encourage creativity in general, but

there are places where it is not appropriate.