2.14

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Questions and Answers

What does the '&' operator indicate in C programming?

The address of a variable (correct)

The object pointed to by a pointer

A pointer's size

The next element in an array

How does pointer incrementation work in C regarding RISC-V integers?

Pointer increments by 8 bytes for each integer

Pointer increments by 2 bytes for each integer

Pointer increments by 4 bytes for each integer (correct)

Pointer increments by 1 byte for each integer

Which procedure in C uses array indices for clearing an array?

clear2

clear0

clear1 (correct)

clear3

What role does modern compiler optimization play in the context of pointers and arrays?

It improves the performance of code that uses pointers. Signup and view all the answers

What is the consequence of using the pointer syntax incorrectly in C?

It might result in incorrect memory access or undefined behavior. Signup and view all the answers

What does the instruction `mv x5, x10` do in the context of the code?

It assigns the address of the array to the pointer p. Signup and view all the answers

What is the purpose of the instruction `sw x0, 0(x5)`?

To set the first element of the array to zero. Signup and view all the answers

Why is the instruction `addi x5, x5, 4` used after the store operation?

To move the pointer p to the next element in the array. Signup and view all the answers

How is the address of the last element of the array calculated?

By multiplying the size by 8 to get the byte address. Signup and view all the answers

What does `bltu x5, x7, loop2` accomplish within the loop?

It tests if the pointer p is less than the last element before the next iteration. Signup and view all the answers

In the assembly code, how does the compiler determine the number of bytes needed for an array of integers?

By multiplying the size of the array by 4 bytes. Signup and view all the answers

What does the `slli x6, x11, 2` instruction do in this context?

Shifts the value of size left to multiply by 4 bytes. Signup and view all the answers

What occurs when p is incremented by 4?

p now references the next integer in the array. Signup and view all the answers

What is the significance of initializing the first element of an array to zero?

It serves as a default starting value for calculations. Signup and view all the answers

How does pointer manipulation enhance performance in array processing?

It allows direct access to memory locations for faster data retrieval. Signup and view all the answers

Study Notes

Two C Procedures for Setting an Array to All Zeros

Two C procedures, clear1 and clear2, are used to set an array to all zeros.
clear1 uses array indices, while clear2 uses pointers.
The address of a variable is indicated by &, and the object pointed to by a pointer is indicated by *.
The declarations declare array and p as pointers to integers.

Array Version of Clear

The array version of clear, clear1, initializes the index i to 0.
To get the address of array[i], the index i is multiplied by 4 to get the byte address.
The byte address is then added to the starting address of the array to get the address of array[i].
The value 0 is stored in the address of array[i].
The index i is then incremented by 1.
The loop test checks if i is less than size.

Pointer Version of Clear

The pointer version of clear, clear2, allocates the parameters array and size to registers x10 and x11, and p to register x5.
The pointer p is assigned to the address of the first element of the array.
The loop body, simply stores 0 in the memory location pointed to by p.
The pointer p is then incremented by 4, which moves it to the next sequential object in memory.
The loop test checks if p is less than the address of the last element of the array.

Modern Compiler Optimization

Modern compilers optimize code to improve performance.
This can be achieved through techniques like loop unrolling or register allocation.
Compiler optimization can make the performance of both the array and pointer versions of clear similar.

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Description

This quiz explores two procedures in C programming used to set an array to all zeros: clear1 using array indices and clear2 using pointers. It highlights the use of addresses and pointer arithmetic for array manipulation. Test your understanding of these concepts and their implementations.