while i'm sure there's many other examples, in that particular case it's just the maximum value of an unsigned 8 bit integer, as defined above on line 1252. it

while i'm sure there's many other examples, in that particular case it's just the maximum value of an unsigned 8 bit integer, as defined above on line 1252. it would be a bit better if it explicitly had a nice #define but recognizing the values of common powers of two (minus one) is a useful code reading skill.