Bits and bit vectors in Perl haven’t changed since the first edition, so there’s not much to update in this chapter. I thought that Abigail’s prime number regex might deserve some space, but it turns out that it didn’t.
I also thought that the octal prefix
0o had made it in since it’s proposal back in the v5.15 days. It had some interesting parsing problems, and eventually the proposal was dropped.
When I last worked on this book, I was running a 32-bit
perl with v5.8. Now I have a 64-bit v5.18. The output of some of the Devel::Peek examples changed a little, so I updated those.
I added an example of using a bit vector to cache the positions of prime numbers. I can create a big string where each bit represents one number. When it’s time to check if a number is prime, I simply check the right bit.
Finally, at the end of the chapter, I updated the URLs for “Further Reading”. In eight years the URLs have moved around a bit.