cpu.js

const createMemory = require("./createMemory")
const instructions = require("./instructions")

class CPU {
  constructor(memory) {
    this.memory = memory
    // prettier-ignore
    this.registerNames = [
      'ip', 'acc',
      'r1', 'r2', 'r3', 'r4',
      'r5', 'r6', 'r7', 'r8'
    ]

    this.registers = createMemory(this.registerNames.length * 2)

    this.registerMap = this.registerNames.reduce((map, name, i) => {
      map[name] = i * 2
      return map
    }, {})
  }

  debug() {
    this.registerNames.forEach((name) => {
      console.log(
        `${name}: 0x${this.getRegister(name).toString(16).padStart(4, "0")}`
      )
    })
    console.log()
  }

  viewMemoryAt(address) {
    const nextEightBytes = Array.from({ length: 8 }, (_, i) =>
      this.memory.getUint8(address + i)
    ).map((v) => `0x${v.toString(16).padStart(2, "0")}`)

    console.log(
      `0x${address.toString(16).padStart(4, "0")}: ${nextEightBytes.join(" ")}`
    )
  }

  getRegister(name) {
    if (!(name in this.registerMap)) {
      throw new Error(`getRegister: No such register '${name}'`)
    }
    return this.registers.getUint16(this.registerMap[name])
  }

  setRegister(name, value) {
    if (!(name in this.registerMap)) {
      throw new Error(`getRegister: No such register '${name}'`)
    }
    return this.registers.setUint16(this.registerMap[name], value)
  }

  fetch() {
    const nextInstructionAddress = this.getRegister("ip")
    const instruction = this.memory.getUint8(nextInstructionAddress)
    this.setRegister("ip", nextInstructionAddress + 1)
    return instruction
  }

  fetch16() {
    const nextInstructionAddress = this.getRegister("ip")
    const instruction = this.memory.getUint16(nextInstructionAddress)
    this.setRegister("ip", nextInstructionAddress + 2)
    return instruction
  }

  execute(instruction) {
    switch (instruction) {
      // Move literal into register
      case instructions.MOV_LIT_REG: {
        const literal = this.fetch16()
        const register = (this.fetch() % this.registerNames.length) * 2
        this.registers.setUint16(register, literal)
        return
      }
      // Move register to register
      case instructions.MOV_REG_REG: {
        const registerFrom = (this.fetch() % this.registerNames.length) * 2
        const registerTo = (this.fetch() % this.registerNames.length) * 2
        const value = this.registers.getUint16(registerFrom)
        this.registers.setUint16(registerTo, value)
        return
      }
      case instructions.MOV_REG_MEM: {
        const registerFrom = (this.fetch() % this.registerNames.length) * 2
        const address = this.fetch16()
        const value = this.registers.getUint16(registerFrom)
        this.memory.setUint16(address, value)
        return
      }
      case instructions.MOV_MEM_REG: {
        const address = this.fetch16()
        const value = this.memory.getUint16(address)
        const registerTo = (this.fetch() % this.registerNames.length) * 2
        this.registers.setUint16(registerTo, value)
        return
      }
      // Add register to register
      case instructions.ADD_REG_REG: {
        const r1 = this.fetch()
        const r2 = this.fetch()
        const registerValue1 = this.registers.getUint16(r1 * 2)
        const registerValue2 = this.registers.getUint16(r2 * 2)
        this.setRegister("acc", registerValue1 + registerValue2)
        return
      }
      case instructions.JMP_NOT_EQ: {
        const value = this.fetch16()
        const address = this.fetch16()

        if (value != this.getRegister("acc")) {
          this.setRegister("ip", address)
        }
        return
      }
    }
  }

  step() {
    const instruction = this.fetch()
    return this.execute(instruction)
  }
}

module.exports = CPU