Assignment#2:	DUE DATE: Monday, March 13, 2005, by Midnight. Email to your section's GA.


Warning: 
  1) For this assignment you must use only the instructions, macros, and 
  directives that are described in lectures 1 to 7. Exception to this is in 
  question 1, where you'll be using the Rint code discussed in Lecture 8 (page 17). 
  
  2) Make sure your program is well commented. 
  
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Programming Exercise 1 (50 points): 
  
  a) (30 points) Write a procedure called multiply that takes two signed 16 bit 
  values and returns the result of their multiplication. You are not allowed to 
  use instructions discussed in Chapter 8, including MUL and IMUL. You should 
  implement multiply by addition. The first argument to multiply is passed 
  through AX register. The second argument is passed through BX. The result of 
  multiplication is returned in EAX. Make sure after execution of multiply all 
  general purpose registers maintain their original value before the call except 
  for EAX which will contain the result of multiplication. 
  
  b) (20 points) To test multiply you'll write a main program that prompts the 
  user to enter two numbers and then output the result of multiplication using 
  multiply as shown below. 
 
  In your main program: You'll have to check that the input value N is within range 
  -32768 <= N <= 32767. If the entered number is out of range your program will 
  issue an error message as shown below and asks the user to enter two new numbers. 
  You should only make the call to multiply if the entered numbers are within 
  acceptable range. After showing the result of multiplication your main program 
  will give the user an option to quit the program. If the user enters y ,Y or any 
  sequence of characters that starts with a lowercase or uppercase Y, the program 
  exits. If the user enters any other character or string of characters the program 
  continues with asking the user to enter two more numbers .... 
    
  Hint: To simplify the code in the main portion of your program you may want to 
  write a procedure that will perform the within range check and sets a flag 
  that you can test after return from the call. 
  
  NOTE: To read signed integer numbers from standard input you can use  
  procedure Rint. The code for this procedure is in page 17 of Lecture 8. Make 
  sure you do the following: 
  
  1) Save this code in a file called Rint.inc 
  
  2) Use an include directive immediately after .code directive to include this 
  file in your program. 
  
  NOTE: Make sure you name your program ass2-1.asm. 
  
  Here are some sample execution scenarios:
   
  C:\ASM>ass2-1 
  Enter the first number: 0 
  Enter the second number: 0 
  0*0=0 
  Quit ? n 
  Enter the first number: 0 
  Enter the second number: 3 
  0*3=0 
  Quit ? Y 
  
  C:\ASM>ass2-1 
  Enter the first number: 3 
  Enter the second number: 0 
  3*0=0 
  Quit ? n 
  Enter the first number: 32767 
  Enter the second number: -32768 
  32767*-32768=-1073709056 
  Quit ? n 
  Enter the first number: -32768 
  Enter the second number: 32767 
  -32768*32767=-1073709056 
  Quit ? No 
  Enter the first number: 32768 
  32768 Is Out of Range ! 
  Enter the first number: 32767 
  Enter the second number: -32769 
  -32769 Is Out of Range ! 
  Enter the first number: 32767 
  Enter the second number: 32767 
  32767*32767=1073676289 
  Quit ? n 
  Enter the first number: -32768 
  Enter the second number: -32768 
  -32768*-32768=1073741824 
  Quit ? n 
  Enter the first number: 1 
  Enter the second number: 5 
  1*5=5 
  Quit ? n 
  Enter the first number: 1 
  Enter the second number: -1 
  1*-1=-1 
  Quit ? n 
  Enter the first number: -1 
  Enter the second number: -1 
  -1*-1=1 
  Quit ? y 
  
  C:\ASM> 
  
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Programming Exercise 2 (50 points): 

  a) (10 points) Write a procedure called DisplayHexDigit that takes as input a 
  number between 0 and 15 stored in BX register and prints it in hexadecimal. 
  
  b) (10 points) Write a procedure called DisplayHexByte that takes as input a 
  number between 0 and 255 stored in BX register and prints it in hexadecimal. 
  Procedure DisplayHexByte should call DisplayHexDigit to print the number. 
  
  c) (15 points) Write a procedure called DisplayHexWord that takes as input a 
  number between 0 and 65535 stored in BX register and prints it in hexadecimal. 
  Procedure DisplayHexWord should call DisplayHexByte to print the number. 
  
  d) (15 points) To test these procedures your main program should read a number 
  from the input between 0 and 65535 and depending on the range that the input 
  number falls call one of the above procedure. 
  
  NOTE: Make sure you name your programs ass2-2-a.asm, ass2-2-b.asm, ass2-2-c.asm 
  and ass2-2-d.asm. To read a number from 
  standard input use the Rint procedure as it was discussed in Question 1. 
  
  Here are some sample execution scenarios: 
  
  C:\ASM>ass2-2 
  0 
  0 
  
  C:\ASM>ass2-2 
  15 
  F 
  
  C:\ASM>ass2-2 
  16 
  10 
  
  C:\ASM>ass2-2 
  255 
  FF 
  
  C:\ASM>ass2-2 
  256 
  0100 
  
  C:\ASM>ass2-2 
  1000 
  03E8 
  
  C:\ASM>ass2-2 
  65535 
  FFFF