PIC C walsh transform issue

hi

i had an idea of making a Musical Water Fountain which is already done before and i googled for it and found a good project on this link

unfortunately i found that they used the "walsh transform" or "Hadamard transform" to identify different frequency levels of sound and that is the issue i face that i can't find a good reference to implement that transform in simple c or for PIC microcontroller so i hope if there any one can help me to find a good source talking about implementation of this transform

regards