OT: one's compliment 8 bit checksum

[geoffrey mendelson]

I need to calculate a one's compliment 8 bit (not 16 bit, not 2's  
compliment) checksum.

What would be really nice is a C subroutine I can call passing the  
number of bytes and a pointer to the data.

Any license I can use will be ok, I don't plan on distributing it, but  
if I do, source code will be included.

It's for use in a program that changes one field in a control file  
that is loaded into the ROM of a 1980's vintage embedded system.

Thanks in advance,

Geoff.
-- 
Geoffrey S. Mendelson,  N3OWJ/4X1GM
My high blood pressure medicine reduces my midichlorian count. :-(