Description:
------------
please see file  "ext/standard/math.c" and function "PHPAPI int _php_math_basetozval(zval *arg, int base, zval *ret)", It's obvious that it does not consider the "NAN" and "INF" problem

Reproduce code:
---------------
<?php
hexdec(INF);
hexdec(NAN);
?>

Expected result:
----------------
to be decided
to be decided

Actual result:
--------------
15  (actually It just convert "f" to decimal)
10  (covert "A" to decimal)