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Hi everyone


First post here on this forum. I'm awfully stuck in an exercice I have to complete as an assignment. I'm studying computer science and this has been my first year.

This is what I am supposed to do:

Your project consists of implementing the following C code:

int f1(int a) {
 if (a < 3)
return (a);
else
return (f2(a-1, a-2) + f2(a-2, a-1));
}
 int f2(int x, int y) {
return 2*f1(x) + y;
}

This is what I have so far:

.text
main: 
	# retrieve input from user
	li $v0, 5     # load code for read int
	syscall     # syscall for read int
	
	# store user input as first operand
	move $a0, $v0     # store read int as argument
	
	# calculate result
	jal f1     # function call
	
	j display

	j exit
	
f1:
        # make room on stack for $ra and $a0
	move $fp, $sp     	# new fp is sp
	addi $sp, $sp, -8     # sp gets bigger
	
        # store both those registers on the stack
	sw $a0, 0($fp)     # store function argument
	sw $ra, -4($fp)     # store return address
	
        # recursive condition
	slti $t0, $a0, 3    # if a < 3, t0 = 1
	li $t1, 1			# Load int into t1 for comparison
	bne $t0, $t1, f1_L1 # Branch if a >= 3	
	move $v0, $a0    # set a0 as result
	j f1_return     # go to return code

        # recursive calls
	f1_L1:
		addi $a1, $a0, -1 # Prepare first argument
		addi $a2, $a0, -2 # Prepare second argument
		jal f2_L1 # Function call
		add $v0, $v0, $v1
		addi $a1, $a0, -2
		addi $a2, $a0, -1
		jal f2_L1
		add $v0, $v0, $v1
		
        # return sequence f1
	f1_return:
                # restore $ra and $a0 registers
		lw $ra, -4($fp)     # restore previous return address
		lw $a0, 0($fp)     # restore previous function argument

		move $sp, $fp     # sp gets smaller (remove frame)
		
		jr $ra     # continue at return address

		# f2
	f2_L1:
		
		# make room on stack for $ra, $a1, $a2
		move $fp, $sp     	# new fp is sp
		addi $sp, $sp, -12     # sp gets bigger
	
        # store all three registers on the stack
		sw $a2, 0($fp)     # store function argument 2
		sw $a1, -4($fp)     # store function argument 1
		sw $ra, -8($sp)		# store return adress
		
		move $a0, $a1 
		jal f1
		li $t0, 2
		mult $v0, $t0
		mflo $v1
		add $v1, $v1, $a2
		
	
        # return sequence f2
	f2_return:
		 # restore $ra, $a1, $a2
		lw $ra, -8($fp)     # restore previous return address
		lw $a1, -4($fp)     # restore previous function argument
		lw $a2, 0($fp)		

		move $sp, $fp     # sp gets smaller (remove frame)
		
		jr $ra     # continue at return address
		
		# display result
	display:
		move $a0, $v0     # store arg for syscall
		li $v0, 1     # load code for display int
		syscall     # syscall for display int
	
		# exit program
	exit:
		li $v0, 10     # load code for exit
		syscall     # syscall for exit

When I run this code, I get an error:

Error in cs06.asm line 42: Runtime exception at 0x00400058: arithmetic overflow

I have highlighted this line in the code.

Anyone sees anything to help me ? Thanks.

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Last Post by PieterA
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Is my explanation of the problem confusing? Or is MIPS not as widespread as I think?

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