nes-emu/registers/InMemoryRegister.js

A NES emulator

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = void 0;
var _helpers = require("../helpers");
/** An 8-bit register with multiple status flags and values that live in RAM. */
class InMemoryRegister {
  constructor() {
    _helpers.WithContext.apply(this);
    this.memorySize = 1;
    this.value = 0;
    this._readOnlyFields = [];
  }

  /** Adds a field of `size` bits named `name`, starting at `startPosition`. */
  addField(name, startPosition) {
    let size = arguments.length > 2 && arguments[2] !== undefined ? arguments[2] : 1;
    Object.defineProperty(this, name, {
      get() {
        return _helpers.Byte.getBits(this.value, startPosition, size);
      },
      set(value) {
        this.value = _helpers.Byte.force8Bit(_helpers.Byte.setBits(this.value, startPosition, size, value));
      }
    });
    return this;
  }

  /** Adds a read-only field of `size` bits named `name`, starting at `startPosition`. */
  addReadOnlyField(name, startPosition) {
    let size = arguments.length > 2 && arguments[2] !== undefined ? arguments[2] : 1;
    // (this performs better than `addField`)
    this._readOnlyFields.push({
      name,
      startPosition,
      size
    });
    this[name] = 0;
    return this;
  }

  /** Sets the value manually (updating internal accessors). */
  setValue(value) {
    this.value = _helpers.Byte.force8Bit(value);
    this._writeReadOnlyFields();
  }

  /** Returns the actual value. */
  readAt() {
    return this.value;
  }

  /** Sets the actual value. */
  writeAt(__, byte) {
    this.setValue(byte);
  }
  _writeReadOnlyFields() {
    for (let {
      name,
      startPosition,
      size
    } of this._readOnlyFields) this[name] = _helpers.Byte.getBits(this.value, startPosition, size);
  }
}
exports.default = InMemoryRegister;