17 March Lab in CSCI 274

Lab goals

• Learn about binary addition and subtration
• Learn a bit about binary fractions
• Modify and run a Java program

Starting off

As usual

• mkdir csci/274/lab07
• chmod go-rx csci/274/lab07
• cd csci/274/lab07
• cp /usr/local/csci/274/lab07/* .

In order to compile Java, you must be logged into either a Sun Sparc or a Digital Alpha workstation. If you are not logged into one of these machines type the following commands:

• xhost +tuxedo
• rlogin tuxedo
• cd csci/274/lab07
• setenv DISPLAY your-machine:0

where your-machine is the name of the computer you are now logged into. You should now see two java source files in your directory, AddEm.java and FloatEm.java.

Adding binary numbers

The Java applet running below adds two binary numbers. The squares in the applet are the two numbers being added. Right now, all of the squares should be black. However, press the mouse button on one of the squares and notice that it changes from black to red. A black square represents the binary value 0, and a red square represents the binary value 1.

The top row of circles represents the carry being propagated through the addition. The bottom row represents the output sum. Play with the applet for a minute. Add 17 (10001) to 63 (111111) and see if you get 80 (1010000). Then replace the 17 with -17 and look for 46 (101110) as the result.

I suspect you've guessed your assignment by now. Yep, you are to modify the file AddEm.java so that it subtracts rather than adds. There really isn't that much you need to do: (1), you need to change the initial carry, m_Carry[0], and (2) you need to change the recomputeOutputs method. If you are really eager you can make other enhancements, such as adding an overflow indicator or printing 0's and 1's in the squares and circles.

You'll need to use pico to modify AddEm.java, javac to recompile the program, and appletviewer to view the result. The sequence of commands for doing this will be:

• pico AddEm.java
• javac AddEm.java
• appletviewer AddEm.html

Good luck.

Binary fractions

The row of squares in the following applet represent a binary fraction. Press on some of the squares and notice that the printed fraction and the sliding bar changes to represent the real number between 0 and 1 corresponding to the fractional bits.

Your assignment for this applet is pretty simple. Set the bits so that they represent a binary fraction very close to .1997. As soon as you have done this, email the fraction to brock@cs.unca.edu.

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