* 判断文件或文件夹是否可写
 * @param    string $file 文件或目录
 * @return    bool
 */
function is_really_writable($file)
{
    if (DIRECTORY_SEPARATOR === '/') {
        return is_writable($file);
    }
    if (is_dir($file)) {
        $file = rtrim($file, '/') . '/' . md5(mt_rand());
        if (($fp = @fopen($file, 'ab')) === false) {
            return false;
        }
        fclose($fp);
        @chmod($file, 0777);
        @unlink($file);
        return true;
    } elseif (!is_file($file) or ($fp = @fopen($file, 'ab')) === false) {
        return false;
    }
    fclose($fp);
    return true;
}

 * 首字母头像
 * @param $text
 * @return string
 */
function letter_avatar($text)
{
    $total = unpack('L', hash('adler32', $text, true))[1];
    $hue = $total % 360;
    list($r, $g, $b) = hsv2rgb($hue / 360, 0.3, 0.9);

    $bg = "rgb({$r},{$g},{$b})";
    $color = "#ffffff";
    $first = mb_strtoupper(mb_substr($text, 0, 1));
    $src = base64_encode('<svg xmlns="http://www.w3.org/2000/svg" version="1.1" height="100" width="100"><rect fill="' . $bg . '" x="0" y="0" width="100" height="100"></rect><text x="50" y="50" font-size="50" text-copy="fast" fill="' . $color . '" text-anchor="middle" text-rights="admin" alignment-baseline="central">' . $first . '</text></svg>');
    $value = 'data:image/svg+xml;base64,' . $src;
    return $value;
}

$str = '';
$timer = $date;
$diff = $_SERVER['REQUEST_TIME'] - $timer;
$day = floor($diff / 86400);
$free = $diff % 86400;
if($day > 0) {
    return $day."天前";
}else{
    if($free>0){
        $hour = floor($free / 3600);
        $free = $free % 3600;
        if($hour > 0){
            if($hour == 24){
                return '昨天 '.date('d',$date);
            }else{
                return $hour."小时前";    
            }
            
        }else{
            if($free>0){
                $min = floor($free / 60);
                $free = $free % 60;
                if($min>0){
                    return $min."分钟前";
                }else{
                    if($free>0){
                        return $free."秒前";
                    }else{
                        return '刚刚';
                    }
                }
            }else{
                return '刚刚';
            }
        }
    }else{
        return '刚刚';
    }
}

}

$age = strtotime($birthday); 
if($age === false){ 
    return false; 
} 
list($y1,$m1,$d1) = explode("-",date("Y-m-d",$age)); 
$now = strtotime("now"); 
list($y2,$m2,$d2) = explode("-",date("Y-m-d",$now)); 
$age = $y2 - $y1; 
if((int)($m2.$d2) < (int)($m1.$d1)) 
    $age -= 1; 
return $age; 

}

{
    $units = array('B', 'KB', 'MB', 'GB', 'TB', 'PB');
    for ($i = 0; $size >= 1024 && $i < 6; $i++) {
        $size /= 1024;
    }
    return round($size, 2) . $delimiter . $units[$i];
}