Please change this c++ code into pep9

Question

Take the following program and translate it into PEP/9 assembly language:

 

#include <iostream>

 

using namespace std;

 

int fib(int n)

{

int temp;

if (n <= 0)

  return 0;

else if (n <= 2)

  return 1;

else {

  temp = fib(n – 1);

  return temp + fib(n-2);

}

}

 

int main()

{

  int num;

  cout << "Which fibonacci number? ";

  cin >> num;

  cout << fib(num) << endl;

  return 0;

}

 

You must use equates to access the stack and follow the call to the function as discussed in the book (pass the parameter, return address, return a value and so on). There are NO global variables in the resulting code (except a global message of "Range num? "). It must be able to do a range greater than 2.

Answer 1

; Fibonacci Program in PEP/9 Assembly

.ORIG 0x1000 ; Program starting address

; Global message "Which fibonacci number? "

PROMPT .STRING "Which fibonacci number? "

NEWLINE .STRING "\n"

; Equates for stack access and function call

.EQU SPREG, 0xFFFC ; Stack pointer register

.EQU RETADDR, 0xFFFA ; Return address register

.EQU FIB_PARAM, 0xFFFE ; Parameter for fib function

; Main program

MAIN:

; Print "Which fibonacci number? "

LDX #PROMPT

JSR PRINT_STRING

; Read user input (integer)

JSR READ_INT

; Store user input (Fibonacci number) in memory

STX FIB_PARAM

; Call fib function

LDX FIB_PARAM

JSR FIB

; Print result (Fibonacci number)

JSR PRINT_INT

; Print newline

LDX #NEWLINE

JSR PRINT_STRING

; Exit program

JSR HALT

; Function to print a string

PRINT_STRING:

LDA ,X ; Load the byte at address X

BEQ DONE_PRINT ; If it's zero (end of string), exit

OUT ; Output the character

INX ; Move to next character

BRA PRINT_STRING

DONE_PRINT:

RTS ; Return from subroutine

; Function to read an integer

READ_INT:

IN ; Read an integer from input (PEP/9 I/O)

STX FIB_PARAM ; Store the integer in FIB_PARAM

RTS

; Function to print an integer

PRINT_INT:

LDA FIB_PARAM ; Load the number to be printed

OUT ; Output the integer

RTS

; Fibonacci function (recursive)

FIB:

LDX FIB_PARAM ; Load the input parameter (n)

CPX #0 ; Compare n with 0

BEQ FIB_ZERO ; If n == 0, return 0

CPX #2 ; Compare n with 2

BLS FIB_TWO ; If n <= 2, return 1

; n > 2: Recursive case

TSX ; Push return address onto stack

STX RETADDR ; Store the return address

; fib(n-1)

LDX FIB_PARAM ; Load n

SUB #1 ; n-1

STX FIB_PARAM ; Update parameter to n-1

JSR FIB ; Recursive call fib(n-1)

LDX RETADDR ; Get return address

TSX ; Push return address onto stack

STX RETADDR ; Store the return address

; fib(n-2)

LDX FIB_PARAM ; Load n

SUB #2 ; n-2

STX FIB_PARAM ; Update parameter to n-2

JSR FIB ; Recursive call fib(n-2)

LDX RETADDR ; Get return address

ADD RETADDR ; Add fib(n-1) + fib(n-2)

RTS

FIB_ZERO:

LDA #0 ; Return 0 for fib(0)

RTS

FIB_TWO:

LDA #1 ; Return 1 for fib(1) or fib(2)

RTS

; End of program

HALT:

.END