Add comment describing the origin of mix64_policy::apply_hash

2021-11-29 06:14:20 +02:00
parent bbd0eedb5f
commit 5e8b6a9e55
1 changed files with 5 additions and 0 deletions
--- a/include/boost/unordered/detail/implementation.hpp
+++ b/include/boost/unordered/detail/implementation.hpp
@ -2632,6 +2632,11 @@ namespace boost {
        static inline SizeT apply_hash(Hash const& hf, T const& x)
        {
          SizeT key = hf(x);
+
+          // "Integer Hash Function", Thomas Wang, 1997
+          // https://gist.github.com/badboy/6267743
+          // http://web.archive.org/web/20071223173210/http://www.concentric.net/~Ttwang/tech/inthash.htm
+
          key = (~key) + (key << 21); // key = (key << 21) - key - 1;
          key = key ^ (key >> 24);
          key = (key + (key << 3)) + (key << 8); // key * 265