snowflake自增ID算法 （PHP版）

/**
* SnowFlake ID Generator
* Based on Twitter Snowflake to generate unique ID across multiple
* datacenters and databases without having duplicates.
*
*
* SnowFlake Layout
*
* 1 sign bit -- 0 is positive, 1 is negative
* 41 bits -- milliseconds since epoch
* 5 bits -- dataCenter ID
* 5 bits -- machine ID
* 12 bits -- sequence number
*
* Total 64 bit integer/string
*/

class SnowFlake
{
/**
* Offset from Unix Epoch
* Unix Epoch : January 1 1970 00:00:00 GMT
* Epoch Offset : January 1 2000 00:00:00 GMT
*/
const EPOCH_OFFSET = 1483200000000;
const SIGN_BITS = 1;
const TIMESTAMP_BITS = 41;
const DATACENTER_BITS = 5;
const MACHINE_ID_BITS = 5;
const SEQUENCE_BITS = 12;

/**
* @var mixed
*/
protected $datacenter_id;

/**
* @var mixed
*/
protected $machine_id;

/**
* @var null|int
*/
protected $lastTimestamp = null;

/**
* @var int
*/
protected $sequence = 1;
protected $signLeftShift = self::TIMESTAMP_BITS + self::DATACENTER_BITS + self::MACHINE_ID_BITS + self::SEQUENCE_BITS;
protected $timestampLeftShift = self::DATACENTER_BITS + self::MACHINE_ID_BITS + self::SEQUENCE_BITS;
protected $dataCenterLeftShift = self::MACHINE_ID_BITS + self::SEQUENCE_BITS;
protected $machineLeftShift = self::SEQUENCE_BITS;
protected $maxSequenceId = -1 ^ (-1 << self::SEQUENCE_BITS);
protected $maxMachineId = -1 ^ (-1 << self::MACHINE_ID_BITS);
protected $maxDataCenterId = -1 ^ (-1 << self::DATACENTER_BITS);

/**
* Constructor to set required paremeters
*
* @param mixed $dataCenter_id Unique ID for datacenter (if multiple locations are used)
* @param mixed $machine_id Unique ID for machine (if multiple machines are used)
* @throws \Exception
*/
public function __construct($dataCenter_id, $machine_id)
{
if ($dataCenter_id > $this->maxDataCenterId) {
throw new \Exception('dataCenter id should between 0 and ' . $this->maxDataCenterId);
}
if ($machine_id > $this->maxMachineId) {
throw new \Exception('machine id should between 0 and ' . $this->maxMachineId);
}
$this->datacenter_id = $dataCenter_id;
$this->machine_id = $machine_id;
}

/**
* Generate an unique ID based on SnowFlake
* @return string
* @throws \Exception
*/
public function generateID()
{
$sign = 0; // default 0
$timestamp = $this->getUnixTimestamp();
if ($timestamp < $this->lastTimestamp) {
throw new \Exception('"Clock moved backwards!');
}
if ($timestamp == $this->lastTimestamp) { //与上次时间戳相等，需要生成序列号
$sequence = ++$this->sequence;
if ($sequence == $this->maxSequenceId) { //如果序列号超限，则需要重新获取时间
$timestamp = $this->getUnixTimestamp();
while ($timestamp <= $this->lastTimestamp) {
$timestamp = $this->getUnixTimestamp();
}
$this->sequence = 0;
$sequence = ++$this->sequence;
}
} else {
$this->sequence = 0;
$sequence = ++$this->sequence;
}
$this->lastTimestamp = $timestamp;
$time = (int)($timestamp - self::EPOCH_OFFSET);
$id = ($sign << $this->signLeftShift) | ($time << $this->timestampLeftShift) | ($this->datacenter_id << $this->dataCenterLeftShift) | ($this->machine_id << $this->machineLeftShift) | $sequence;
return (string)$id;
}

/**
* Get UNIX timestamp in microseconds
*
* @return int  Timestamp in microseconds
*/
private function getUnixTimestamp()
{
return floor(microtime(true) * 1000);
}
}