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index.js
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index.js
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const instructions = [
// mov eax, 0
{ code: 0xb8, operands: [0x00, 0x00, 0x00, 0x00], mnemonic: "mov" },
{ code: 0xc7, operands: [0xc0, 0x00, 0x00, 0x00, 0x00], mnemonic: "" },
// mov ebx, 10
{ code: 0xbb, operands: [0x0a, 0x00, 0x00, 0x00], mnemonic: "mov" },
// add eax, ebx
{ code: 0x03, operands: [0xc3], mnemonic: "add" },
// cmp eax, 50
{ code: 0x3d, operands: [0x32, 0x00, 0x00, 0x00], mnemonic: "cmp" },
// je done
{ code: 0x74, operands: [0x07], mnemonic: "je" },
// jmp loop
{ code: 0xeb, operands: [0xf4], mnemonic: "jmp" },
// done:
{ code: 0xc3, mnemonic: "" }
];
class CPU {
constructor() {
this.registers = new Uint32Array(8);
this.memory = new Uint8Array(1024);
this.flags = {
zero: false,
carry: false,
overflow: false,
negative: false
};
this.eip = 0;
}
run() {
while (this.eip < instructions.length) {
const instruction = instructions[this.eip];
const [operands, operandSize] = this.parseOperands(instruction.operands);
switch (instruction.mnemonic) {
case "mov":
this.mov(operands);
break;
case "add":
this.add(operands);
break;
case "sub":
this.sub(operands);
break;
case "jmp":
this.jmp(operands);
break;
case "cmp":
this.cmp(operands);
break;
case "je":
this.je(operands);
break;
default:
console.error(`Unknown instruction: ${instruction.mnemonic}`);
return;
}
this.eip += instruction.length || 1;
}
}
parseOperands(operands) {
const operandSize = operands.shift();
const operandValues = operands.map((operand) => {
if (typeof operand === "number") {
return operand;
}
if (operand.startsWith("r")) {
return this.registers[parseInt(operand.slice(1))];
}
if (operand.startsWith("0x")) {
return parseInt(operand.slice(2), 16);
}
return parseInt(operand);
});
return [operandValues, operandSize];
}
mov([src, dest]) {
dest = this.resolveRegister(dest);
this.writeOperand(dest, src);
}
add([a, b]) {
const result = a + b;
this.flags.carry = result > 0xffffffff;
this.flags.overflow = (a > 0 && b > 0 && result < 0) || (a < 0 && b < 0 && result >= 0);
this.flags.zero = result === 0;
this.flags.negative = result < 0;
b = this.resolveRegister(b);
this.writeOperand(b, result);
}
sub([a, b]) {
const result = a - b;
this.flags.carry = result < 0;
this.flags.overflow = (a > 0 && b < 0 && result < 0) || (a < 0 && b > 0 && result >= 0);
this.flags.zero = result === 0;
this.flags.negative = result < 0;
b = this.resolveRegister(b);
this.writeOperand(b, result);
}
jmp([address]) {
this.eip = address;
}
cmp([a, b]) {
const result = a - b;
this.flags.carry = result < 0;
this.flags.zero = result === 0;
this.flags.negative = result < 0;
}
je([address]) {
if (this.flags.zero) {
this.eip = address;
}
}
resolveRegister(register) {
if (typeof register === "string" && register.startsWith("r")) {
register = parseInt(register.slice(1));
}
return this.registers[register];
}
writeOperand(dest, value) {
if (typeof dest === "string" && dest.startsWith("r")) {
dest = parseInt(dest.slice(1));
}
if (dest < 8) {
this.registers[dest] = value;
} else {
this.memory[dest - 8] = value;
}
}
}
const cpu = new CPU();
cpu.registers[0] = 0; // eax
cpu.registers[3] = 50; // esi
cpu.memory[0] = 0xeb; // jmp loop
cpu.memory[1] = 0xf9; // offset from current address (-7)
cpu.run();
console.log(cpu.registers[0]); // should output 55