CS 230 Winter 2024 Assignment 4

1.  Assume  that  an  array  has  been  initialized  with  integers,  where the  array  location  is  in register $1 and the array length is in register $2. Write an  assembly  program  that

updates the contents of the array as follows:

. negative numbers are replaced by the square of the number

. positive numbers are replaced by 10 times the number

. zero is unchanged

For example, if the array started with values [-7,  0,  15,  -3,  6], when the program is done the array will contain the values  [49,  0,  150,  9,  60] .

The contents of registers $1 and $2 must be the same at the end of your program as   they were at the beginning; however their values may change within the body of the   program. If the values of registers $1 and $2 are incorrect, then correctness marks for this question will be 0.

Notes:

. Test your solution using the arraydump front end.  For more information about how arraydump works, see the solutions for Tutorial 06 .

. You must use as few registers as possible to receive full marks. The  exact number required for full marks will not be published; this  is something you need to judge  for yourself.

. You should not avoid using registers by temporarily saving values  to  memory.

Memory access with the lw and sw instructions is very slow compared to accessing data in registers, so it would be counter-productive to  save  a  value  to  memory rather than use a register.

. You cannot use the stack for this question.

Submit the file a4q1.asm.

2.  Credit card numbers include a check digit that can be used to detect errors when someone enters the card number for online purchases. One common method for generating a  check digit  is the  Luhn  formula. A  description of the algorithm  can  be found here:

https://en.wikipedia.org/wiki/Luhn_algorithm

Assume that an array has been initialized with non-negative integers, where the array location  is  in  register $1 and the  array  length  is  in  register $2. The  contents of the array represent all the digits of a credit card except the  check  digit.  In  other  words,  each element of the array will be a single digit in the range 0 to 9 inclusive.

Write an assembly program that computes the check digit based on Luhn’s algorithm and places the check digit in register $3. The leftmost digit of the credit card will appear at index position 0 in the array. The rightmost digit of the credit card will appear in the last index position in the array.

Examples:

. The array with values  [1, 2, 3, 4]  has check digit of 4, since

1 + 2 × 2 + 3 + 4 × 2 = 16. You can find the check digit by taking this sum, multiplying by 9, and looking at the ones digit of the product:

i.e.  16 × 9 = 144, and the  remainder when you divide  144 ÷ 10 is 4. . The array with values [5, 4, 3, 2, 1] has a check digit of 5, since 5 × 2 = 10 and the sum of the digits of  10 is  1 + 0 = 1, and

1 + 4 + 2 × 3 + 2 + 1 × 2 =  15, and

15 × 9 = 135, and

the remainder when you divide 135 ÷ 10 is 5.

. The array with values  [7, 9, 9,  2, 7, 3, 9, 8, 7,  1]  has check digit of 3 (Wikipedia example) .

Test your solution using the array front end.

Submit the file a4q2.asm.

3.  Hangman is a simple 2-player game where one player picks  a  word  or  phrase  and  the other player tries to guess it. The word to guess is marked out by underscores, where each underscore represents one letter.  The guesser picks one letter at a time.  If the  letter is in the word then all occurrences of that letter replace the dash(es) at the appropriate   place(s). The game continues  until either the guesser  picks all the  letters  in the word, or   until they reach a predetermined limit of incorrect guesses.

(a)  Write an assembly program that reads a word entered by the player. The word is composed of one or more lowercase letters only followed by a new line character. Then read a single, lowercase letter followed by a newline character which is a guess. Print the state of the game after one guess, where if the guessed letter appears in    the word then it is printed in its correct spot(s), otherwise a underscore is printed in place of the letter in the word. A newline character should be printed at the end of the state. The ASCII code value of a newline character is the hex number 0xA.  For example, if the user enters the word waterloo, then enters the letter o, the following characters will be printed on their own line:

oo

Test your solution using the noargs front end.

Submit the file a4q3a.asm.

(b)  Write a more complete version of the game that reads a word entered by the player, and accepts multiple guesses one letter at a time. This continues until either the player guesses all the letters in the original word or until they have made six guesses where the letter guessed is not in the word. You are not required to keep track of which letters have been guessed. After each guess, the state of the game as described in part (a) should appear on its own line.  If the player guesses all the letters, then print an uppercase W, followed by a newline character. If the player runs out of guesses, then print an uppercase L, followed by a newline character.