Can't understand the opeartion orig ^ (orig + j) in arith stage

[leetking]

I am sorry for asking the question here.

I'm a beginner in fuzzing, thanks for the awesome AFL to guide me into fuzzing. but, when I read the source of AFL, I can't understand the operation described as the issue title (the source is https://github.com/google/AFL/blob/master/afl-fuzz.c#L5523). According to my understanding, if it is to perform arithmetic addition and subtraction, then directly reduce the price, why still do xor operation?