FWHT - Fast Walsh Hadamard Transform in C
 BSD license.
 by Sven Nilsen, 2012
 http://www.cutoutpro.com
 
 Version: 0.000 in angular degrees version notation
 http://isprogrammingeasy.blogspot.no/2012/08/angular-degrees-versioning-notation.html

This implementation was made without looking at other FWHT algorithms,
so I release under its own license.

	// Compile unit tests with GCC.
	gcc -o fwht-test fwht-test.c -Wall

	// Run code.
	./fwht-test
 
Fast Walsh Hadamard Transform
 
The input souce has to be in size 2^n.

Example use: You have two similar images where the camera
is moved or rotated slightly and you want to find the
transformation of the camera movement. You then take
two 4x4 pieces of each image and transform each color channel
with FWHT and then take the differences, sum them
and you will have a number that tells you how similar the
two pieces are.
 
When you apply a FWHT twice, you get the same as before,
only multiplied with a factor of the size of the data.