[GENERAL] Equivalent of PHP "hex2bin()"

[Stephen Cook]

PHP has functions "bin2hex()" and "hex2bin()", and I have to deal with 
the results in PostgreSQL.

These functions "Returns an ASCII string containing the hexadecimal 
representation of |str|. The conversion is done byte-wise with the 
high-nibble first" and "Decodes a hexadecimally encoded binary string". 
Basically you can take binary data and each byte becomes two hexadecimal 
characters.

Is there anything in PostgreSQL that can do this already? I'm sure I can 
work it out but it can't hurt to ask first.

-- Stephen