CS 366 - Functions

For this assignment, you will write functions in SPIM. These functions MUST follow the MIPS Convention for Register Usage. You are to write functions that will:

• Read in a floating point array.
• Output a floating point array.
• Determine the smaller of two floating point parameters.
• Sort a floating point array..
• An function that loops through two arrays and compares the corrsponding values in each position of the array.

Your program may have other functions, but the above must be included.

Your program is to have a data section that contains two floating point arrays. Each array should be able to store up to 100 values; however, may actually hold fewer values. All access to the arrays and any supporting variables (like a length or size information) from the functions must be made through the use of parameters. Any information about the arrays that is accessed directly by a function will result in a grade of zero for the assignment.

Your program is to perform the following steps:

1. Fill in the first array with values from input using a function.
2. Fill in the second array with values from input using a function.
3. Print out the values in each array using a function. This function should be called once for each array.
4. Call the function that will loop through the arrays comparing the corresponding values in each position of the array. This function is to print out both corresponding values and then print out the smaller of the two values. This function MUST call the function that determines the smaller of two floating point parameters to find the smaller value. If the arrays are not the same size, stop comparing values once you get to the end of the smaller array.
5. Sort both floating point arrays. This function should be called once for each array. This function MUST call the function that determines the smaller of two floating point parameters to find the smaller value.
6. Again call the function that will loop through the arrays comparing the corresponding values in each position of the array. This function is to print out both corresponding values and then print out the smaller of the two values. This function MUST call the function that determines the smaller of two floating point parameters to find the smaller value. If the arrays are not the same size, stop comparing values once you get to the end of the smaller array.

Specifics about each function you are to write

• Read in a floating point array.

  The function to read in a floating point array should prompt the user for values and read in values until either the value 0.0 is read in or the array is filled. The value of 0.0 is not to be stored in the array. This function must pass back or return the number of values actually stored in the array. A possible C prototype for this function could be:

       void readInput (float arr[], int maxSize, int* actualSize);
  

• Output a floating point array.

  The function to output the floating point array should list the numbers in some uniform manner (like two per line). A possible C prototype for this function could be:

       void printArray (float arr[], int actualSize);
  

• Determine the smaller of two floating point parameters.

  The function that determines the smaller of the two floating point numbers is to return the value of 1 if the first parameter is smaller than the second parameter. This function is to return the value of 0 if the first parameter is not smaller than the second parameter. This function is simply an isLessThan() function. Note: this function is not to use the floating point comparison operations. You are to write your own algorithm to determine if the first floating point parameter is smaller than the second floating point parameter. This function may use any of the "integer comparison" operation. Thus you may wish to seperate a floating point value into its three parts of sign, mantissa and exponent and work with these. Remember that floating point numbers use a "Sign & Magnitude" style of representation. Thus, when comparing two negative numbers, the value with the larger magnitude is the smaller of the two numbers. The exponent and the mantissa combine to make up the magnitude of the floating point number. A possbile C prototype for this function could be:

       int isLessThan (float val1, float val2);
  

• Sort a floating point array.

  The function to sort a floating point array can use any algorithm that you like; however, you must use your comparison function to perform any comparison of two floats. Note that a less than function can be used to determine any of the six relational operations.

  Relational Operation	Function
  X < Y	isLessThen(X, Y) == 1
  X <= Y	isLessThen(Y, X) == 0
  X > Y	isLessThen(Y, X) == 1
  X >= Y	!isLessThen(X, Y) == 0
  X == Y	(isLessThen(X, Y) == 0) && (isLessThan(Y, X) == 0)
  X != Y	(isLessThen(X, Y) == 1) || (isLessThan(Y, X) == 1)

  A possible C prototype for this function could be:

       void sort (float *arr[], int actualSize);
  

• An function that loops through two arrays and compares the corrsponding values in each position of the array.

  For the function that loops through two arrays and compares the corresponding values in each position of the arrays, you are to print out the smaller value at each position. Remember you are to use your comparison function to perform any comparison of two floating point numbers. The C code to do this is:

       /* assume we have parameters arr1, arr2, len1 and len2 */
  
       /* determine the size of the smaller array */
       if (len1 < len2)
            len = len1;
       else
            len = len2;
  
       for (i = 0; i < len; i++)
           {
            printf ("The smaller value at position %d is ", i);
            if (isLessThen(arr1[i], arr2[i]) == 1)
                printf ("%f\n", arr1[i]);
            else
                printf ("%f\n", arr2[i]);
           } 
  

The programs will be graded based on how they execute on xspim running in the CS Department computers. You are to submit your program electronically using the the turnin command with the project name of mp3. Your program must be well commented and use blank lines to separate logical sections of your code.

You can earn 10 points extra credit on this assignment by using a recursive quicksort or recursive mergesort sorting algorithm for your sorting function. Note that the recursive sorting function will still need to use the "isLessThan()" function to compare two floating point numbers. If you are doing this, you MUST have your program print out the appropriate message:

     This program uses the recursive quicksort algorithm.
or
     This program uses the recursive mergesort algorithm.

Alternative Register Names in SPIM

Input and Output in SPIM

• The print_string service expects the address to start a null-terminated character string. The directive .asciiz creates a null-terminated character string.
• The read_int, read_float and read_double services read an entire line of input up to and including the newline character.
• The read_string service has the same semantices as the C library routine fgets().
  • It reads up to n-1 characters into a buffer and terminates the string with a null character.
  • If fewer than n-1 characters are in the current line, it reads up to and including the newline and terminates the string with a null character.
• The sbrk service returns the address to a block of memory containing n additional bytes. This would be used for dynamic memory allocation.
• The exit service stops a program from running.

The following special characters are used with character strings in SPIM. The special characters follow the C language convention:

Character	Encoding Sequence
Newline	\n
Tab	\t
Double quote	\"