nes-emu/memory/RewiredMemoryChunk.js

A NES emulator

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = void 0;
var _MemoryChunk = _interopRequireDefault(require("./MemoryChunk"));
function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; }
/**
 * A memory segment that accepts a `mapping` object which translates internal addresses.
 * For example, in PPU's Palette RAM, $10/$14/$18/$1C are mirrors of $00/$04/$08/$0C, so:
 * mapping = { 0x10: 0x00, 0x14: 0x04, 0x18: 0x08, 0x1c: 0x0c }
 */
class RewiredMemoryChunk extends _MemoryChunk.default {
  constructor(bytes, mapping) {
    super(bytes);
    this.mapping = mapping;
  }

  /**
   * Creates a mapping object from a `ranges` array.
   * For example:
   * The list [{ from: 10, size: 5, to: 1 }]...
   * ...creates the mapping { 10: 1, 11: 2, 12: 3, 13: 4, 14: 5 }
   */
  static createMapping(ranges) {
    const mapping = {};
    for (let range of ranges) {
      for (let i = 0; i < range.size; i++) {
        mapping[range.from + i] = range.to + i;
      }
    }
    return mapping;
  }

  /** Reads a byte from `address`, following mirroring rules. */
  readAt(address) {
    if (this.mapping[address] != null) address = this.mapping[address];
    this._assertValidAddress(address);
    return this.bytes[address];
  }

  /** Writes a `byte` to `address`, following mirroring rules. */
  writeAt(address, byte) {
    if (this.mapping[address] != null) address = this.mapping[address];
    this._assertValidAddress(address);
    this.bytes[address] = byte;
  }
}
exports.default = RewiredMemoryChunk;