[logicallee]

Thank you. This is very good and thank you for sharing. You should probably copy the usage information from your comment here to the top of the file, so they're not separated.

I tried it and got the same result you suggested (I used a code running site but it shouldn't matter, the VM it runs in should have virtualized operations that shouldn't slow it down by a complete order of magnitude so I roughly trust the results I'm seeing.)

FYI, here is the output with 10m items. (It times out if I try to increase it further, but that is just because the code-running site kills programs that run longer than a set time)

  ht_size: 10000000
  sizeof(int): 4
  seed: 256
  start run
  roll 64: -2004260032
  time (seconds:+nanoseconds) 1s:270464 ns
  sequential run: roll 64: -2004260032
  time (seconds:+nanoseconds) 0s:281244 ns

so if that is 1.27 sec for 10mill it should obviously be around 12 seconds for 100 million. Just brutal. I had no idea things could be so bad.

Thanks so much for sharing your program with us!