sub2ind_mex

A very fast sub2ind routine in mex ( C )

This function operates in the same manner as the 'sub2ind' method. However, this method is quite faster. It is very similar to the sub2ind.m code.
Example :
>> a = [ 50 50 50 ];
>> b = [ 1 30 49 ];
>> x = sub2ind(a,b,b,b)
x =

1 73980 122449

>> xx = sub2ind_mex(a,b,b,b)

xx =

1 73980 122449

I would like to acknowledge "Marco" from the following thread. He began this bit of code a while ago and posted it here. I have simply taken it and improved its performance a bit. Thank you Marco, I do hope you don't mind what I have done here.
http://www.mathworks.com/matlabcentral/newsreader/view_thread/262036

Update :::
I had unfortunately made a pretty big error in the code. The first while loop did not have sound logic as it was counting backwards. This would work for symmetric arrays only.
My apologies everyone!