php绝对路径转相对路径

/**
 * 绝对路径转成相对 路径
 * $path相对于$base的相对路径
 * @param string $base
 * @param string $path
 * 思路：去除共同部分
 */

function rela_pos($base, $path)
{
    $base = explode('/', trim($base,'/'));
    $path = explode('/', trim($path,'/'));
    $ln1 = count($base);
    $ln2 = count($path);
    if ($ln1 > $ln2) {
        $i = 0;
        foreach ($path as $k => $v) {
            if ($v == $base[$k]) {
                $i++;
            }else{
                break;
            }
        }
    } else {
        $i = 0;
        foreach ($base as $k1 => $v1) {
            if ($v1 == $path[$k1]) {
                $i++;
            }else{
                break;
            }
        }
    }
    array_splice($base, 0, $i);
    array_splice($path, 0, $i);
    //当前两个路径有相同的根目录
    $b_len=count($base)-1;
    $st='';
   for($j=0;$j<$b_len;$j++){
    $st.='../';
   }
    return $st.implode('/',$path);
}

$a = '/c/a/b/c/d/t/w/e.php';
$b = '/a/b/12/34/c.php';
$res=rela_pos($a,$b);

var_dump($res);