Fastest Way To Find Mismatch Positions Between Two Strings of the Same Length

Question

I have a millions of pairs of string of same length which I want to compare and find the position where it has mismatches.

For example for each $str1 a

Answer 1

The fastest way to compare the strings to find differences would be to XOR each byte of them together then test for zero. If I had to do this I would just write a program in C to do the difference job rather than writing a C extension to Perl, then I would run my C program as a subprocess of Perl. The exact algorithm would depend on the length of the strings and the amount of data. However this would not take more than 100 lines of C. In fact, if you want to maximize speed, a program to XOR bytes of fixed-length strings and test for zero could be written in assembly language.