Simple CPU Emulator

simple_cpu_emu.cpp

#include <iostream>

// Instruction
/*
	NOP							: No Operation
	LOADI	dest, imm			: Load immidiate to 'dest' register
	LOADA	dest, addr			: Load address to 'dest' register
	ADD		dest, op1, op2		: Add 'op1' and 'op2' and save to 'dest' register
	SUB		dest, op1, op2		: Subtract 'op1' and 'op2' and save to 'dest' register
	PRINT	registers			: Print registers
*/

// Sample program, add two numbers
int program[] = {
	// Data
	12,
	13,
	// Main program
	0x00000000, // NOP
	0x00000002, // LOADA	R0, 0x00
	0x00040102, // LOADA	R1, 0x04
	0x01000203, // ADD		R2, R0, R1
	0x00000205, // PRINT	R2
};

// ------------ Registers ------------
int registers[32] = {0};

// ------------ Instruction implementation ------------
void nop(int code)
{
	// No operation
	return;
}

void loadi(int code)
{
	int dest = (code & 0x0000FF00) >> 8;
	int imm = (code & 0xFFFF0000) >> 16;
	registers[dest] = imm;
	return;
}

void loada(int code)
{
	int dest = (code & 0x0000FF00) >> 8;
	int addr = (code & 0xFFFF0000) >> 16;
	void* memAddr = (void*)&program[0] + addr;
	registers[dest] = *(int*)memAddr;
	return;
}

void add(int code)
{
	int dest = (code & 0x0000FF00) >> 8;
	int op1 = (code & 0x00FF0000) >> 16;
	int op2 = (code & 0xFF000000) >> 24;
	registers[dest] = registers[op1] + registers[op2];
	return;
}

void sub(int code)
{
	int dest = (code & 0x0000FF00) >> 8;
	int op1 = (code & 0x00FF0000) >> 16;
	int op2 = (code & 0xFF000000) >> 24;
	registers[dest] = registers[op1] + registers[op2];
	return;
}

void print(int code)
{
	int reg = (code & 0x0000FF00) >> 8;
	std::cout << registers[reg] << std::endl;
	return;
}

typedef void (*instr)(int);

int main()
{
	instr instrFun[6] = {
		&nop,
		&loadi,
		&loada,
		&add,
		&sub,
		&print
	};
	
	int instrCount = (sizeof(program) / sizeof(int));
	int startPoint = 2; // Start at index 2 of the program array (as seen in the program above)
	
	// Execute all instructions in the program
	for(int pc = startPoint; pc < instrCount; pc++)
	{
		// Decode the opcode
		int code = program[pc] & 0x000000FF;
		// Call the opcode
		(*instrFun[code])(program[pc]);
	}
	
}