区块链挖矿算法优化：从尾部到头部校验零值

本文介绍了一种优化区块链挖矿算法的方法，将难度校验从哈希值的尾部改为头部，并增加了最大尝试次数的限制，以提高挖矿效率并避免无限循环。

设计需求

将挖矿难度从尾部改为前面，即要求哈希值前面有指定个数的零。
增加一个计数器 maximumNonce，限制挖矿的次数，避免挖矿时间过长。

计算过程

在原有代码基础上，只需要修改 pattern 的生成方式，将其从尾部零改为前面零。同时，在 mine 函数中增加一个循环，限制挖矿的次数不超过 maximumNonce。

完整代码

var difficulty = 4;        // number of zeros required at front of hash
var maximumNonce = 500000; // limit the nonce to this so we don't mine too long

// NOTE: Because there are 16 possible characters in a hex value, each time you increment
// the difficulty by one you make the puzzle 16 times harder. In my testing, a difficulty
// of 6 requires a maximumNonce well over 500,000,000.

/////////////////////////
// global variable setup
/////////////////////////
var pattern = '';
for (var x = 0; x < difficulty; x++) {
  pattern += '0';
}

/////////////////////////
// functions
/////////////////////////
function sha256(block, chain) {
  // calculate a SHA256 hash of the contents of the block
  return CryptoJS.SHA256(getText(block, chain));
}

function updateState(block, chain) {
  // set the well background red or green for this block
  if ($('#block' + block + 'chain' + chain + 'hash').val().substr(0, difficulty) === pattern) {
    $('#block' + block + 'chain' + chain + 'well').removeClass('well-error').addClass('well-success');
  }
  else {
    $('#block' + block + 'chain' + chain + 'well').removeClass('well-success').addClass('well-error');
  }
}

function updateHash(block, chain) {
  // update the SHA256 hash value for this block
  $('#block' + block + 'chain' + chain + 'hash').val(sha256(block, chain));
  updateState(block, chain);
}

function updateChain(block, chain) {
  // update all blocks walking the chain from this block to the end
  for (var x = block; x <= 5; x++) {
    if (x > 1) {
      $('#block' + x + 'chain' + chain + 'previous').val($('#block' + (x - 1).toString() + 'chain' + chain + 'hash').val());
    }
    updateHash(x, chain);
  }
}

function mine(block, chain, isChain) {
  for (var x = 0; x <= maximumNonce; x++) {
    $('#block' + block + 'chain' + chain + 'nonce').val(x);
    $('#block' + block + 'chain' + chain + 'hash').val(sha256(block, chain));
    if ($('#block' + block + 'chain' + chain + 'hash').val().substr(0, difficulty) === pattern) {
      if (isChain) {
        updateChain(block, chain);
      }
      else {
        updateState(block, chain);
      }
      break;
    }
    if (x === maximumNonce) {
      console.log('Maximum nonce reached, mining stopped.');
    }
  }
}

通过以上优化，可以有效提高挖矿效率，并避免因难度过高而导致的长时间挖矿。