index.js

const {
  BN,
  keccak,
  keccak256,
  rlphash,
  zeros,
  bufferToInt,
  TWO_POW256
} = require('ethereumjs-util')
const ethHashUtil = require('./util.js')
const xor = require('buffer-xor')
const async = require('async')

var Ethash = (module.exports = function (cacheDB) {
  this.dbOpts = {
    valueEncoding: 'json'
  }
  this.cacheDB = cacheDB
  this.cache = false
})

Ethash.prototype.mkcache = function (cacheSize, seed) {
  // console.log('generating cache')
  // console.log('size: ' + cacheSize)
  // console.log('seed: ' + seed.toString('hex'))
  const n = Math.floor(cacheSize / ethHashUtil.params.HASH_BYTES)
  var o = [keccak(seed, 512)]

  var i
  for (i = 1; i < n; i++) {
    o.push(keccak(o[o.length - 1], 512))
  }

  for (var _ = 0; _ < ethHashUtil.params.CACHE_ROUNDS; _++) {
    for (i = 0; i < n; i++) {
      var v = o[i].readUInt32LE(0) % n
      o[i] = keccak(xor(o[(i - 1 + n) % n], o[v]), 512)
    }
  }

  this.cache = o
  return this.cache
}

Ethash.prototype.calcDatasetItem = function (i) {
  const n = this.cache.length
  const r = Math.floor(
    ethHashUtil.params.HASH_BYTES / ethHashUtil.params.WORD_BYTES
  )
  var mix = Buffer.from(this.cache[i % n])
  mix.writeInt32LE(mix.readUInt32LE(0) ^ i, 0)
  mix = keccak(mix, 512)
  for (var j = 0; j < ethHashUtil.params.DATASET_PARENTS; j++) {
    var cacheIndex = ethHashUtil.fnv(i ^ j, mix.readUInt32LE((j % r) * 4))
    mix = ethHashUtil.fnvBuffer(mix, this.cache[cacheIndex % n])
  }
  return keccak(mix, 512)
}

Ethash.prototype.run = function (val, nonce, fullSize) {
  fullSize = fullSize || this.fullSize
  const n = Math.floor(fullSize / ethHashUtil.params.HASH_BYTES)
  const w = Math.floor(
    ethHashUtil.params.MIX_BYTES / ethHashUtil.params.WORD_BYTES
  )
  const s = keccak(Buffer.concat([val, ethHashUtil.bufReverse(nonce)]), 512)
  const mixhashes = Math.floor(
    ethHashUtil.params.MIX_BYTES / ethHashUtil.params.HASH_BYTES
  )
  var mix = Buffer.concat(Array(mixhashes).fill(s))

  var i
  for (i = 0; i < ethHashUtil.params.ACCESSES; i++) {
    var p =
      (ethHashUtil.fnv(i ^ s.readUInt32LE(0), mix.readUInt32LE((i % w) * 4)) %
        Math.floor(n / mixhashes)) *
      mixhashes
    var newdata = []
    for (var j = 0; j < mixhashes; j++) {
      newdata.push(this.calcDatasetItem(p + j))
    }

    newdata = Buffer.concat(newdata)
    mix = ethHashUtil.fnvBuffer(mix, newdata)
  }

  var cmix = Buffer.alloc(mix.length / 4)
  for (i = 0; i < mix.length / 4; i = i + 4) {
    var a = ethHashUtil.fnv(
      mix.readUInt32LE(i * 4),
      mix.readUInt32LE((i + 1) * 4)
    )
    var b = ethHashUtil.fnv(a, mix.readUInt32LE((i + 2) * 4))
    var c = ethHashUtil.fnv(b, mix.readUInt32LE((i + 3) * 4))
    cmix.writeUInt32LE(c, i)
  }

  return {
    mix: cmix,
    hash: keccak256(Buffer.concat([s, cmix]))
  }
}

Ethash.prototype.cacheHash = function () {
  return keccak256(Buffer.concat(this.cache))
}

Ethash.prototype.headerHash = function (header) {
  return rlphash(header.slice(0, -2))
}

/**
 * Loads the seed and the cache given a block nnumber
 * @method loadEpoc
 * @param number Number
 * @param cm function
 */
Ethash.prototype.loadEpoc = function (number, cb) {
  var self = this
  const epoc = ethHashUtil.getEpoc(number)

  if (this.epoc === epoc) {
    return cb()
  }

  this.epoc = epoc

  // gives the seed the first epoc found
  function findLastSeed (epoc, cb2) {
    if (epoc === 0) {
      return cb2(zeros(32), 0)
    }

    self.cacheDB.get(epoc, self.dbOpts, function (err, data) {
      if (!err) {
        cb2(data.seed, epoc)
      } else {
        findLastSeed(epoc - 1, cb2)
      }
    })
  }

  /* eslint-disable handle-callback-err */
  self.cacheDB.get(epoc, self.dbOpts, function (err, data) {
    if (!data) {
      self.cacheSize = ethHashUtil.getCacheSize(epoc)
      self.fullSize = ethHashUtil.getFullSize(epoc)

      findLastSeed(epoc, function (seed, foundEpoc) {
        self.seed = ethHashUtil.getSeed(seed, foundEpoc, epoc)
        var cache = self.mkcache(self.cacheSize, self.seed)
        // store the generated cache
        self.cacheDB.put(
          epoc,
          {
            cacheSize: self.cacheSize,
            fullSize: self.fullSize,
            seed: self.seed,
            cache: cache
          },
          self.dbOpts,
          cb
        )
      })
    } else {
      // Object.assign(self, data)
      self.cache = data.cache.map(function (a) {
        return Buffer.from(a)
      })
      self.cacheSize = data.cacheSize
      self.fullSize = data.fullSize
      self.seed = Buffer.from(data.seed)
      cb()
    }
  })
  /* eslint-enable handle-callback-err */
}

Ethash.prototype._verifyPOW = function (header, cb) {
  var self = this
  var headerHash = this.headerHash(header.raw)
  var number = bufferToInt(header.number)

  this.loadEpoc(number, function () {
    var a = self.run(headerHash, Buffer.from(header.nonce, 'hex'))
    var result = new BN(a.hash)
    /* eslint-disable standard/no-callback-literal */
    cb(
      a.mix.toString('hex') === header.mixHash.toString('hex') &&
        TWO_POW256.div(new BN(header.difficulty)).cmp(result) === 1
    )
    /* eslint-enable standard/no-callback-literal */
  })
}

Ethash.prototype.verifyPOW = function (block, cb) {
  var self = this
  var valid = true

  // don't validate genesis blocks
  if (block.header.isGenesis()) {
    cb(true) // eslint-disable-line standard/no-callback-literal
    return
  }

  this._verifyPOW(block.header, function (valid2) {
    valid &= valid2

    if (!valid) {
      return cb(valid)
    }

    async.eachSeries(
      block.uncleHeaders,
      function (uheader, cb2) {
        self._verifyPOW(uheader, function (valid3) {
          valid &= valid3
          if (!valid) {
            cb2(Boolean(valid))
          } else {
            cb2()
          }
        })
      },
      function () {
        cb(Boolean(valid))
      }
    )
  })
}