Fibonacci in veeAsm

veeAsmFibonacci

//!ssvasm

$require_registers(4);

$define(R0, 		0);
$define(R1, 		1);
$define(R2, 		2);
$define(ROutput,	3); 




// _______________________________
// 	FN_MAIN function
//		* entrypoint
//		* returns in ROutput 
// _______________________________

$label(FN_MAIN);

	// Compute the 10th fibonacci number

	// Load constants
	loadIntCVToR(R0, 10);

	// Save registers
	pushRVToS(R0);	
	pushRVToS(R1);

	// Push args
	pushRVToS(R0);

	// Call func
	callPI(FN_FIB);

	// Get return value
	moveRVToR(ROutput, R0);

	// Pop args
	popSV();

	// Restore registers
	popSVToR(R1);
	popSVToR(R0);



	// Push output to stack
	pushRVToS(ROutput);

	halt();




// _______________________________
// 	FN_FIB function
//		* needs 1 int argument
//		* uses R0, R1
//		* returns in R0 
// _______________________________

$label(FN_FIB);

	// Get arg from stack
	moveSBOVToR(R0, 2);

	// Check if arg is < 2 (put compare result in R1)
	compareIntRVIntCVToR(R1, R0, 2);

	// Return arg if arg < 2
	goToPIIfCompareRVSmaller(FN_FIB_RET_ARG, R1);




	// Else return fib(arg - 1) + fib(arg - 2)

	// Calculate fib(arg - 1)

		// Save registers
		pushRVToS(R0);

		// Push args
		pushIntCVToS(1);
		pushRVToS(R0);
		subtractInt2SVs();		

		// Call func
		callPI(FN_FIB);

		// Get return value
		// Return value is in R0, move it to R2
		moveRVToR(R2, R0);

		// Pop args
		popSV();

		// Restore registers
		popSVToR(R0);		

		// Push fib(arg - 1) on stack
		pushRVToS(R2);
		
	// Calculate fib(arg - 2)
		// Save registers
		pushRVToS(R0);

		// Push args
		pushIntCVToS(2);
		pushRVToS(R0);
		subtractInt2SVs();		

		// Call func
		callPI(FN_FIB);

		// Get return value
		// Return value is in R0, move it to R2
		moveRVToR(R2, R0);

		// Pop args
		popSV();

		// Restore registers
		popSVToR(R0);		

		// Push fib(arg - 2) on stack
		pushRVToS(R2);

	// Return fib(arg - 1) + fib(arg + 1)
		addInt2SVs();
		popSVToR(R0);
		returnPI();



	$label(FN_FIB_RET_ARG);
		returnPI();