64-bit speedups

I tried to find out how much performance increase a 64-bit compile will give compared to the 32-bit compile. I tested three different programs: my Connect 4, Cake and KingsRow. I also have a speedup reported by Ed Gilbert for his international checkers program, KingsRow-10. Here are the numbers:

• KingsRow: 5.8%
  
• Cake: 6.4%
  
• Connect 4: 11.6%
  
• KingsRow-10: 42.9%
  

This list shows that all programs are able to benefit from the 64-bit compile, although the gain is rather moderate for all programs except KingsRow-10. Why can some programs benefit more than others? Probably this has to do with how much they make use of 64-bit operations. For example, my Connect 4 program uses a 64-bit representation of the board. KingsRow and Cake use 32-bit representations and don't really have any use for the larger word size on the 64-bit machine. KingsRow-10 on the other hand also uses 64-bit numbers for its board representation and benefits much more than any other program on the list.

With all these numbers I have to add that there are some points to be considered: The KingsRow 32/64-bit versions don't seem to search the exact same tree - in kN/s searched, KR-64 was 5.8% faster, but its search time was only 2.6% lower. Additionally, KR wasn't using the endgame database during this test, since it doesn't recognize it for some reason on my system. Cake 32/64 searches exactly the same number of nodes on the one-minute search I used for this test. Cake32 makes use of some assembler instructions which Cake64 does not, so probably the speed difference would be a bit larger if I found out how to program these functions in 64-bit assembler. The same is true for Connect 4 (For the experts: I don't have a LSB function in assembler for the 64-bit versions).