What is the PHP equivalent of MySQL's UNHEX()?

What is the PHP equivalent of MySQL's UNHEX()?

What is the PHP equivalent of MySQL's UNHEX()?
For instance, the following query and PHP function should provide the same
value.
SELECT UNHEX(c1) AS unhexed_c1 FROM table;
$unhexed_c1=PHPs_UNHEX_Equivalent($c1);