PHP 最小化一个计算中的操作数不一定会提高它的性能?? 和 本身操作最好用+= 或者 *= /=

 

 

 

set_time_limit(1200);
class PerformanceTest
{
    private $time;
    private $memory;

    public function begin()
    {
        $this->time = $this->getTime();
        $this->memory = $this->getMemory();
    }

    public function end()
    {

        $this->time   = $this->getTime()   - $this->time;
        $this->time   = round($this->time,23);//在这里才能格式化时间
        $this->memory = $this->getMemory() - $this->memory;
        $this->memory = $this->convert($this->memory);
        echo "time:{$this->time}秒<br />";
        echo "memory:{$this->memory}<br />";
        return $this->time;
    }

    public function getSpentTime()
    {
        return $this->time;
    }    
    public function getTime() 
    {  
        list($usec, $sec) = explode(" ", microtime());
        return ((float)$usec + (float)$sec);
    }

    public function getMemory()
    {
        return memory_get_usage();
    }

    public function convert(int $size)
    { 
        if(!$size)
        {
            return '0 b';
        }
        $size = abs($size);
        $unit=array('b','kb','mb','gb','tb','pb');
        return @round($size/pow(1024,($i=floor(log($size,1024)))),2).' '.$unit[$i]; 
    } 

}

function poly(array $a,float $x,int $degree)
{
    $result = $a[0];
    $xpwr = $x;
    for($i=1;$i<=$degree;$i++)
    {
        $result += $a[$i] * $xpwr;
        $xpwr = $x * $xpwr;
    }
    return $result;
}

function poly2(array $a,float $x,int $degree)
{
    $result = $a[0];
    $xpwr = $x;
    for($i=1;$i<=$degree;$i++)
    {
        $result = $result + $a[$i] * $xpwr;//效率低于+=
        $xpwr = $x * $xpwr;
    }
    return $result;
}

function polyh(array $a,float $x,int $degree)
{
    $result = $a[$degree];
    for($i=$degree-1;$i>=0;$i--)
    {
        $result = $a[$i] + $x*$result;
    }
    return $result;
}

function buildData(int $len)
{
    $ret = [];
    if($len>0)
    {
        for($i=0;$i<$len;$i++)
        {
            $ret[] = randomFloat(0,100); 
        }
    }
    return $ret;
}
function randomFloat($min = 0, $max = 1) 
{  
    return $min + mt_rand() / mt_getrandmax() * ($max - $min);  
}  
$a = new PerformanceTest();
$count = 10000;
$x = (double)randomFloat(0,100); 
$v= buildData($count+1);
$cmp = 0;
$cmp2 = 0;
$loop=0;
Loop:
$a->begin();
poly($v,$x,$count);
$a->end();
$poly = $a->getSpentTime();
$a->begin();
polyh($v,$x,$count);
$a->end();
$polyh = $a->getSpentTime();
$a->begin();
poly2($v,$x,$count);
$a->end();
$poly2 = $a->getSpentTime();

if($polyh - $poly<0)
{
    $cmp++;
}
if($poly2 - $poly <0)
{
    $cmp2++;
}
$loop++;
if($loop < 1000)
{
    goto Loop;
}
var_dump($cmp);
var_dump($cmp2);
/**

time:0秒
memory:0 b
time:0.0010001659393311秒
memory:0 b
time:0.00099992752075195秒
memory:0 b
time:0秒
memory:0 b
time:0.00099992752075195秒
memory:0 b
int(554) int(238)

**/
exit;