Question

3. [30] Consider the following C code: float f(float *a, int n) { { float prod = 1.0f; for (int i = 0; i < n; ++i) if (a[i] != 0.0f) { prod *= a[i]; return prod; The above code computes the product of nonzero elements in the array a. float* createArray (int size) { float *a = (float *) malloc(size + sizeof(float)); for (int i = 0; i < size; ++i) { // 50% chance that a[i] is 0.0f, random value on the range // [0.76, 1.26] otherwise. float r = rand() / (float) RAND MAX; a[i] = r < 0.5f ? 0.0f : r + 0.26f; return a; The above helper function allocates an array of the specified size such that each element has a 50% chance of being zero. a. (10) Write a main() function that creates an array a using createArray(10000), and then measures time taken to run fla). We'll cover basic instrumentation in lectures and labs. Don't forget the free the memory allocated for a! b. (10) In your main() function, create a new array b containing the same elements as a but with every 0.0f replaced by 1.0f. Also write a new function g that is equivalent to f but without the zero (i.e., if a[i] != 0.0f) check. Calling g(b) should be functionally equivalent to calling fla) because multiplication by 1.0 is a no-op. Measure the time taken to run g(b) - is it faster than calling f(a)? Compile with-Og. Explain why this might be the case in your code comments. Don't forget the free the memory allocated for b! c. (10) In your main() function, create a new array c containing only the nonzero elements in a (i.e., c will almost certainly have fewer elements than a). Measure the time taken to run g(c) - is it faster than calling f(a) and/or g(b)? Compile with -Og. Explain why this might be the case in your code comments. Don't forget the free the memory allocated for c! Name your source file 6-3.C

Answer 1

The question involves creating C functions to measure performance differences in array processing with various optimizations, requiring a main() function, memory management, and performance analysis.

Step-by-step explanation:

The pertains to writing C code that deals with arrays, memory allocation, and performance measurement. The main() function needs to be written to create an array using create Array(10000), measure the time it takes to compute the product of its non-zero elements with function f, and then deallocate the memory.

Additionally, the student is asked to perform optimizations by creating new arrays with modified elements to compare performance enhancements and provide explanations for observed differences in execution speed. In the main() function, the student will use createArray to create an array a, then measure the execution time of f(a) and finally free the allocated memory using free(). A new array b will be created that contains the same elements as a but replaces every 0.0f with 1.0f to avoid the conditional check in the function f.

The student will write a function g, call g(b), measure execution time, and then free the memory. The performance difference is analyzed assuming the code is compiled with -Og. A new array c will be created containing only the non-zero elements of a, and the student will measure the time to run g(c). After memory deallocation, performance comparisons with f(a) and g(b) will be drawn, with reasons explained within comments.

Answer 2

The student is tasked with writing C code to measure the execution time of functions calculating the product of array elements. The assignment involves array manipulation, time measurement, and performance comparison under different conditions. Proper memory management with free() is also a critical part of this task.

Step-by-step explanation:

The student is asking for help with a C programming assignment. Specifically, the task involves creating several arrays with randomly generated values according to given rules, and then measuring the execution time of certain functions when applied to these arrays. The functions in question calculate a product of array elements under varying conditions. The student must also ensure to free the memory allocated to avoid memory leaks.

a. Main Function for Execution Time of f(a)

Write a main() function that calls createArray with an argument of 10000 to create an array a. Use clock or another time-measuring function to calculate the duration of the f function execution. Remember to use free() to deallocate memory.

b. Array b and Execution Time of g(b)

Create a new array b with the same elements as a but replace each 0.0f with 1.0f. Write a function g that is similar to f but without the zero-check. Measure the execution time of g(b) and compare it to the execution time of f(a). Discuss why there might be a performance difference.

c. Array c and Execution Time of g(c)

Create a new array c containing only the nonzero elements of a. Measure how long it takes to run g(c) and compare this time to those of f(a) and g(b). The performance difference can be attributed to the number of elements and conditional checks present in each version of the array.