I added the hash function from hashmap and changed mapping.c to use power of two hash tables. you can get the patch from http://laramies.com/hash.patch
I benchmarked this against pike 7.9 using pike -x benchmark and a couple of benchmarks we wrote to test our critbit trees. In some benchmarks (like Mapping insert) it leads to about 10% performance increase. Others dont profit that much. I ran the benchmarks on my atom and a core i7.
