Chapter 8 Exercises

Construct a new H1 assembler instruction Exercise 1: Construct a new H1 assembler instruction with semantics: retn x ; o <= x <= 255 pc = mem[sp++]; sp = sp + x;

Create the following H1 instruction: Exercise 2: Create the following H1 instruction: Use this instruction to implement the C++ code cora ; ac = sp + ac; # cora (convert relative address) void foo () { int x = 6; int * p; p = &x cout << *p << endl; } int main() { foo();

Exercise 3: Draw a picture of H1 memory upon completion of the line labeled (A) in the following program: #include <iostream> using namespace std; int x = 100; void fr(int &z) { z = z+ 5; // A } void ft(int &y) { y = y + 1; fr(y); void main() { ft(x); cout << “x = “ << x << endl;

Prof Dos Reis suggested the following solution to this problem: Exercise 4: In the Chapter 7 quiz I asked that you write the H1 assembler code that can execute a function be calling the address of the function as it is stored in another variable. Prof Dos Reis suggested the following solution to this problem: foo: ... ; whatever code is appropriate for foo ret p: dw foo @call dw E000 ; opcode for call ;;; now we execute foo() ld p add @call ; construct “call *p” st *+1 ; place it in the line of execution exec: dw 0 ; execute it now ... ; rest of code

Exercise 4 (continued): In C++ it is possible to define a pointer variable of type “function”. For example, if is a function then the following is a variable, p, that can hold the address of this function as in void foo() {...} void (*p)(); p = &f;

Exercise 4 (continued): Draw the H1 memory configuration diagram as if this program were written in H1 and currently executing the line labeled (X). #include <iostream> using namespace std; void a() { cout << “A” << endl; } void b() { cout << “B” << endl; // (X) void foo(void (*p)()) { p(); int main () { foo(b); foo(a);

Exercise 4 (continued): Write the H1 program of the C++ program on the previous slide.

This is Problem 8.41. What is happening here? Exercise 5: This is Problem 8.41. What is happening here? #include <iostream> using namespace std; int x = 1, y = 2; void f(int &x) { x = x+ 5; cout << x << endl; } int main() { f(x+y+5); cout << x << " " << y << endl;

Exercise 6: In C and C++ arrays do not “know” their own length. So when we pass an array to a function we also need to pass the “length” of the array meaning the number of entries in the array or the maximum index value that are currently in use. Write an H1 assembler program that implements the following C++ function, creates a global array and then populates some but not all of its elements. // finds the index of the largest element in // arg1 in the index range [0,end], end >= 0. int getMaxIndex(int [] a, int end) { int temp = a[0], ndx = 0; for (int i = 1; i <= end; i++) { if (a[i] > temp) { ndx = i; temp = a[i]; } return ndx;

Title: Write