雪花算法简单描述：
最高位是符号位，始终为0，不可用。
41位的时间序列，精确到毫秒级，41位的长度可以使用69年。时间位还有一个很重要的作用是可以根据时间进行排序。 10位的机器标识，10位的长度最多支持部署1024个节点。 12位的计数序列号，序列号即一系列的自增id，可以支持同一节点同一毫秒生成多个ID序号，12位的计数序列号支持每个节点每毫秒产生4096个ID序号。 看的出来，这个算法很简洁也很简单，但依旧是一个很好的ID生成策略。其中，10位器标识符一般是5位IDC+5位machine编号，唯一确定一台机器。 $this->maxWorkerId || $workerId < 0) { throw new Exception("worker Id can't be greater than {$this->maxWorkerId} or less than 0"); } if ($datacenterId > $this->maxDatacenterId || $datacenterId < 0) { throw new Exception("datacenter Id can't be greater than {$this->maxDatacenterId} or less than 0"); } $this->workerId = $workerId; $this->datacenterId = $datacenterId; $this->sequence = $sequence; } public function nextId() { $timestamp = $this->timeGen(); if ($timestamp < $this->lastTimestamp) { $diffTimestamp = bcsub($this->lastTimestamp, $timestamp); throw new Exception("Clock moved backwards. Refusing to generate id for {$diffTimestamp} milliseconds"); } if ($this->lastTimestamp == $timestamp) { $this->sequence = ($this->sequence + 1) & $this->sequenceMask; if (0 == $this->sequence) { $timestamp = $this->tilNextMillis($this->lastTimestamp); } } else { $this->sequence = 0; } $this->lastTimestamp = $timestamp; $gmpTimestamp = gmp_init($this->leftShift(bcsub($timestamp, self::TWEPOCH), $this->timestampLeftShift)); $gmpDatacenterId = gmp_init($this->leftShift($this->datacenterId, $this->datacenterIdShift)); $gmpWorkerId = gmp_init($this->leftShift($this->workerId, $this->workerIdShift)); $gmpSequence = gmp_init($this->sequence); return gmp_strval(gmp_or(gmp_or(gmp_or($gmpTimestamp, $gmpDatacenterId), $gmpWorkerId), $gmpSequence)); } protected function tilNextMillis($lastTimestamp) { $timestamp = $this->timeGen(); while ($timestamp <= $lastTimestamp) { $timestamp = $this->timeGen(); } return $timestamp; } protected function timeGen() { return floor(microtime(true) * 1000); } // 左移 << protected function leftShift($a, $b) { return bcmul($a, bcpow(2, $b)); }}