Commits on Feb 26, 2022

1. robin_hood.h: Change hash val shifts for info and idx generation …

   Instead of generating the `info` hash bits with a mask + shift, we can
   just use an unsigned shift from the end as that will bring in zeros.
   
   With that change the `idx` hash bits can start from the begining so we
   no longer need to shift out the `info` hash bits.
   
   Saves 2x instructions. Only ALU but this function is in the critical
   path.
   
   There does not appear to be any issue with false hits changing the tag
   bits used.
   
   False Tag Match Rates:
   
                         :   New,   Cur
   
   Insert Seq Ints:
   2^10                  : 2.539, 2.832
   2^12                  : 3.076, 3.003
   2^14                  : 2.960, 3.497
   2^16                  : 4.048, 4.306
   2^18                  : 4.543, 4.732
   2^20                  : 5.182, 5.553
   2^22                  : 5.579, 5.557
   2^24                  : 6.237, 6.017
   2^26                  : 6.599, 6.432
   
   Insert Rand Ints (seed = 0):
   2^10                  : 2.637, 4.199
   2^12                  : 2.979, 3.613
   2^14                  : 3.662, 3.955
   2^16                  : 4.309, 4.849
   2^18                  : 4.626, 4.564
   2^20                  : 4.849, 5.044
   2^22                  : 6.050, 5.279
   2^24                  : 5.664, 6.350
   2^26                  : 6.640, 6.771
   
   Insert Strings:
   All Words(0)          : 4.974, 5.231
   10k Words(1)          : 3.550, 4.000
   URLS(2)               : 5.548, 5.683
   URLS(2) w/ "http://"  : 5.466, 5.831
   URLS(2) w/ "https://" : 5.569, 5.761
   
   [0]: https://github.com/dwyl/english-words
   [1]: https://github.com/first20hours/google-10000-english
   [2]: https://www.domcop.com/top-10-million-websites

   

   goldsteinn committed Feb 26, 2022
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