To convert the descriptive entity to the ASCII entity would require a translation from one to the other. You could do this by building an array of all characters with descriptive entities and their corresponding ASCII entity, and then make use of the
strtr function.
You could build the array dynamically by checking all characters whose
htmlentities value is not the same as their character value from the
chr function.
However, HTML makes use of a much larger character set than ASCII for descriptive entities. If you do make it dynamically, consider outputting it in the same syntax as a PHP array and then saving that statically, as to avoid re-processing every time that you want to use these entities.