On the "other" test set, my approach fares far more within my expectations, but here the number of elements returned seems to become significant over the number of string joins:

                           Rate split1 substr1 map_split subst map_spl
+it_join using_str_bit_ops_and_tr
split1                   1.74/s     --    -94%     -100% -100%        
+  -100%                 -100%
substr1                  30.5/s  1650%      --      -93%  -94%        
+   -94%                  -96%
map_split                 455/s 26002%   1392%        --  -13%        
+   -15%                  -34%
subst                     520/s 29765%   1607%       14%    --        
+    -3%                  -25%
map_split_join            534/s 30577%   1653%       18%    3%        
+     --                  -23%
using_str_bit_ops_and_tr  692/s 39604%   2169%       52%   33%        
+    29%                    --

[download]

So, you will need to always benchmark with real data! ;)

In reply to Re^3: Challenge: CPU-optimized byte-wise or-equals (for a meter of beer) by Corion
in thread Challenge: CPU-optimized byte-wise or-equals (for a meter of beer) by dragonchild

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