I looked for a Perl module that would do this with 'C' XS code and couldn't find one. I found one module with the right functionality, but alas it was pure Perl and not very fast. That surprised me because I've seen similar buffer comparison questions before.
in reply to Fast Identification Of String Difference
The 'C' code in a C program for something like this would be very fast. I haven't written an XS module myself yet and I don't know how efficient the transfer of information is between Perl and C. The hard part isn't the C code, it is how to interface it with Perl.
As far as assembly language goes, for comparing byte buffers together, in Intel x86 assembly, there is a single machine instruction that can do this. That would be as fast as it could be done.
If anybody writes an XS module to do this, I would like to see it and would like to help with it if desired.