Pokemon Gen 4 PCD -> WC in JS

PCDWC4.js

const fs = require('fs');
const path = require('path');

function mu32(a, b) {
  var ah = (a >> 16) & 0xffff, al = a & 0xffff;
  var bh = (b >> 16) & 0xffff, bl = b & 0xffff;
  var high = ((ah * bl) + (al * bh)) & 0xffff;
  return (((high << 16)>>>0) + (al * bl)) & 0xffffffff;
}

function LCRNG(seed) {
  return (mu32(seed, 0x41C64E6D) + 0x00006073) >>> 0;
}

function ShuffleArray(pkmBuffer, shiftValue) {
  const blockPositions = [
    [0, 0, 0, 0, 0, 0, 1, 1, 2, 3, 2, 3, 1, 1, 2, 3, 2, 3, 1, 1, 2, 3, 2, 3],
    [1, 1, 2, 3, 2, 3, 0, 0, 0, 0, 0, 0, 2, 3, 1, 1, 3, 2, 2, 3, 1, 1, 3, 2],
    [2, 3, 1, 1, 3, 2, 2, 3, 1, 1, 3, 2, 0, 0, 0, 0, 0, 0, 3, 2, 3, 2, 1, 1],
    [3, 2, 3, 2, 1, 1, 3, 2, 3, 2, 1, 1, 3, 2, 3, 2, 1, 1, 0, 0, 0, 0, 0, 0],
  ];

  const newBlocks = [pkmBuffer.slice(0, 8)];

  for (let block = 0; block < 4; block += 1) {
    const position = 32 * blockPositions[block][shiftValue];
    newBlocks.push(pkmBuffer.slice(8 + position, 8 + (position + 32)));
  }

  newBlocks.push(pkmBuffer.slice(136, 236));

  return Buffer.concat(newBlocks);
}

function getPKM(pcdBuffer) {
  if (pcdBuffer.readUInt8(0) !== 1) {
    return pcdBuffer;
  }

  const pkmBuffer = pcdBuffer.slice(8, 244);

  const pv = pkmBuffer.readUInt32LE(0);
  const chk = pkmBuffer.readUInt16LE(6);

  const shiftvalue = ((pv & 0x3E000) >> 0xD) % 24;

  let seed = chk;

  const decrypted = Buffer.alloc(236);

  decrypted.writeUInt32LE(pv, 0);
  decrypted.writeUInt32LE(pkmBuffer.readUInt32LE(4), 4);

  // Decrypt
  for (let i = 8; i < 236; i += 2) {
    if (i === 136) {
      seed = pv;
    }
    seed = LCRNG(seed);
    decrypted.writeUInt16LE((pkmBuffer.readUInt16LE(i)) ^ (seed >>> 0x10), i);
  }

  return Buffer.concat([pcdBuffer.slice(0, 8), ShuffleArray(decrypted, shiftvalue), pcdBuffer.slice(244, pcdBuffer.length)]);
}

function getPKMFromPCD(dir) {
  const paths = fs.readdirSync(dir);
  fs.mkdirSync(path.join(dir, '/wcs/'));

  for (let i = 0; i < paths.length; i++) {
    if (paths[i].endsWith('.pcd')) {
      const pcdBuffer = fs.readFileSync(paths[i]);
      const pkmBuffer = getPKM(pcdBuffer);

      fs.writeFileSync(path.join(dir, '/wcs/', paths[i].substring(0, paths[i].length - 4) + '.wc4'), pkmBuffer);
    }
  }
}

getPKMFromPCD('./');