strings, bytes: improve IndexAny and LastIndexAny performance

For the case of a pattern containing multi-byte rune, the time complexity of the
previous algorithm is O(nm), and if both input arguments are long, the search
performance will be poor. This CL improves the searching performance for these
cases by using IndexRune, which is mainly implemented with IndexByte and Index.
As IndexByte and Index are specially optimized with some powerful instructions
for short patterns (an UTF8 rune is 1 to 4 bytes), so they can help to reduce the
runtime complexity of IndexAny and LastIndexAny.

Another optimization method is using hash table, however, the actual test results
show that using indexrune is better, and the space complexity is lower.

There are two fast paths in IndexAny and LastIndexAny for cases where the length
of the input arguements are 1, and their locations are not exactly the same, which
is determined based on the actual test results.

Benchmarks on arm64 and amd64:

name                        old time/op  new time/op  delta
pkg:strings goos:linux goarch:arm64
IndexAnyASCII/1:1-8         23.7ns ± 3%  28.5ns ± 0%  +20.15%  (p=0.008 n=5+5)
IndexAnyASCII/1:2-8         18.0ns ± 0%  33.1ns ± 0%  +83.67%  (p=0.008 n=5+5)
IndexAnyASCII/1:4-8         20.0ns ± 0%  36.0ns ± 0%  +80.00%  (p=0.029 n=4+4)
IndexAnyASCII/1:8-8         36.1ns ± 0%  36.0ns ± 0%     ~     (p=0.095 n=5+4)
IndexAnyASCII/1:16-8        48.1ns ± 0%  36.0ns ± 0%  -25.19%  (p=0.029 n=4+4)
IndexAnyASCII/1:32-8        72.1ns ± 0%  36.0ns ± 0%  -50.01%  (p=0.008 n=5+5)
IndexAnyASCII/1:64-8         120ns ± 0%    39ns ± 0%  -67.83%  (p=0.008 n=5+5)
IndexAnyASCII/16:1-8        73.0ns ± 0%  28.5ns ± 0%  -60.95%  (p=0.008 n=5+5)
IndexAnyASCII/16:2-8        76.8ns ± 0%  77.0ns ± 0%     ~     (p=1.000 n=5+5)
IndexAnyASCII/16:4-8        83.2ns ± 1%  83.0ns ± 0%     ~     (p=0.770 n=5+5)
IndexAnyASCII/16:8-8         111ns ± 1%   107ns ± 0%   -3.25%  (p=0.008 n=5+5)
IndexAnyASCII/16:16-8        139ns ± 1%   137ns ± 0%   -1.58%  (p=0.008 n=5+5)
IndexAnyASCII/16:32-8        199ns ± 1%   197ns ± 0%   -1.20%  (p=0.008 n=5+5)
IndexAnyASCII/16:64-8        307ns ± 0%   313ns ± 0%   +1.82%  (p=0.016 n=5+4)
IndexAnyASCII/256:1-8        674ns ± 0%    65ns ± 0%  -90.31%  (p=0.008 n=5+5)
IndexAnyASCII/256:2-8        678ns ± 0%   683ns ± 0%   +0.68%  (p=0.008 n=5+5)
IndexAnyASCII/256:4-8        685ns ± 0%   683ns ± 0%   -0.29%  (p=0.000 n=5+4)
IndexAnyASCII/256:8-8        711ns ± 0%   708ns ± 0%   -0.48%  (p=0.008 n=5+5)
IndexAnyASCII/256:16-8       740ns ± 0%   740ns ± 0%     ~     (p=0.444 n=5+5)
IndexAnyASCII/256:32-8       799ns ± 0%   798ns ± 0%   -0.18%  (p=0.008 n=5+5)
IndexAnyASCII/256:64-8       910ns ± 0%   914ns ± 0%   +0.44%  (p=0.016 n=4+5)
IndexAnyUTF8/1:1-8          27.1ns ± 0%  19.0ns ± 0%  -29.79%  (p=0.008 n=5+5)
IndexAnyUTF8/1:2-8          44.1ns ± 0%  33.0ns ± 0%  -25.17%  (p=0.008 n=5+5)
IndexAnyUTF8/1:4-8          46.1ns ± 0%  33.1ns ± 0%  -28.29%  (p=0.016 n=4+5)
IndexAnyUTF8/1:8-8          85.1ns ± 0%  33.0ns ± 0%  -61.18%  (p=0.008 n=5+5)
IndexAnyUTF8/1:16-8          110ns ± 1%    36ns ± 0%  -67.27%  (p=0.008 n=5+5)
IndexAnyUTF8/1:32-8          188ns ± 0%    36ns ± 0%  -80.85%  (p=0.008 n=5+5)
IndexAnyUTF8/1:64-8          332ns ± 0%    39ns ± 0%     ~     (p=0.079 n=4+5)
IndexAnyUTF8/16:1-8          293ns ± 0%    54ns ± 0%  -81.56%  (p=0.008 n=5+5)
IndexAnyUTF8/16:2-8          563ns ± 0%   349ns ± 0%  -37.98%  (p=0.008 n=5+5)
IndexAnyUTF8/16:4-8          546ns ± 1%   349ns ± 0%  -36.10%  (p=0.000 n=5+4)
IndexAnyUTF8/16:8-8         1.22µs ± 0%  0.35µs ± 0%  -71.39%  (p=0.008 n=5+5)
IndexAnyUTF8/16:16-8        1.63µs ± 1%  0.42µs ± 0%  -73.98%  (p=0.008 n=5+5)
IndexAnyUTF8/16:32-8        2.87µs ± 0%  0.42µs ± 0%  -85.22%  (p=0.008 n=5+5)
IndexAnyUTF8/16:64-8        5.18µs ± 0%  0.47µs ± 0%  -90.98%  (p=0.008 n=5+5)
IndexAnyUTF8/256:1-8        4.26µs ± 0%  0.47µs ± 0%  -88.85%  (p=0.000 n=4+5)
IndexAnyUTF8/256:2-8        8.62µs ± 0%  5.15µs ± 0%  -40.21%  (p=0.008 n=5+5)
IndexAnyUTF8/256:4-8        8.25µs ± 0%  5.15µs ± 0%  -37.50%  (p=0.016 n=5+4)
IndexAnyUTF8/256:8-8        19.2µs ± 1%   5.2µs ± 0%  -73.08%  (p=0.016 n=5+4)
IndexAnyUTF8/256:16-8       25.6µs ± 1%   6.3µs ± 0%  -75.32%  (p=0.008 n=5+5)
IndexAnyUTF8/256:32-8       45.6µs ± 0%   6.3µs ± 0%  -86.15%  (p=0.008 n=5+5)
IndexAnyUTF8/256:64-8       82.4µs ± 0%   7.0µs ± 0%  -91.53%  (p=0.016 n=5+4)
LastIndexAnyASCII/1:1-8     23.0ns ± 0%  33.5ns ± 0%  +45.65%  (p=0.008 n=5+5)
LastIndexAnyASCII/1:2-8     24.5ns ± 0%  33.5ns ± 0%  +36.73%  (p=0.016 n=4+5)
LastIndexAnyASCII/1:4-8     27.5ns ± 0%  35.5ns ± 0%  +29.09%  (p=0.008 n=5+5)
LastIndexAnyASCII/1:8-8     44.5ns ± 0%  35.5ns ± 0%  -20.13%  (p=0.008 n=5+5)
LastIndexAnyASCII/1:16-8    56.5ns ± 0%  35.5ns ± 0%  -37.15%  (p=0.008 n=5+5)
LastIndexAnyASCII/1:32-8    80.3ns ± 0%  35.5ns ± 0%  -55.79%  (p=0.000 n=5+4)
LastIndexAnyASCII/1:64-8     129ns ± 0%    40ns ± 0%  -68.85%  (p=0.008 n=5+5)
LastIndexAnyASCII/16:1-8    72.8ns ± 0%  72.7ns ± 0%   -0.19%  (p=0.016 n=4+5)
LastIndexAnyASCII/16:2-8    75.4ns ± 0%  75.1ns ± 0%     ~     (p=0.127 n=5+5)
LastIndexAnyASCII/16:4-8    81.9ns ± 1%  80.2ns ± 0%   -2.00%  (p=0.008 n=5+5)
LastIndexAnyASCII/16:8-8     110ns ± 1%   108ns ± 0%   -1.46%  (p=0.008 n=5+5)
LastIndexAnyASCII/16:16-8    138ns ± 1%   134ns ± 0%   -3.18%  (p=0.008 n=5+5)
LastIndexAnyASCII/16:32-8    198ns ± 0%   197ns ± 0%   -0.51%  (p=0.008 n=5+5)
LastIndexAnyASCII/16:64-8    309ns ± 0%   313ns ± 0%   +1.30%  (p=0.008 n=5+5)
LastIndexAnyASCII/256:1-8    652ns ± 0%   653ns ± 0%   +0.21%  (p=0.008 n=5+5)
LastIndexAnyASCII/256:2-8    656ns ± 0%   656ns ± 0%     ~     (all equal)
LastIndexAnyASCII/256:4-8    663ns ± 0%   663ns ± 0%     ~     (p=0.444 n=5+5)
LastIndexAnyASCII/256:8-8    691ns ± 0%   690ns ± 0%     ~     (p=0.079 n=4+5)
LastIndexAnyASCII/256:16-8   719ns ± 0%   715ns ± 0%   -0.53%  (p=0.000 n=5+4)
LastIndexAnyASCII/256:32-8   779ns ± 0%   780ns ± 0%   +0.13%  (p=0.029 n=4+4)
LastIndexAnyASCII/256:64-8   890ns ± 0%   894ns ± 0%   +0.45%  (p=0.008 n=5+5)
LastIndexAnyUTF8/1:1-8      31.6ns ± 0%  33.5ns ± 0%   +6.01%  (p=0.008 n=5+5)
LastIndexAnyUTF8/1:2-8      48.6ns ± 0%  33.5ns ± 0%  -30.99%  (p=0.008 n=5+5)
LastIndexAnyUTF8/1:4-8      48.6ns ± 0%  33.5ns ± 0%  -31.13%  (p=0.000 n=5+4)
LastIndexAnyUTF8/1:8-8      89.6ns ± 0%  33.5ns ± 0%  -62.56%  (p=0.008 n=5+5)
LastIndexAnyUTF8/1:16-8      113ns ± 1%    36ns ± 0%  -68.47%  (p=0.000 n=5+4)
LastIndexAnyUTF8/1:32-8      190ns ± 0%    36ns ± 0%  -81.26%  (p=0.029 n=4+4)
LastIndexAnyUTF8/1:64-8      327ns ± 0%    40ns ± 0%  -87.77%  (p=0.008 n=5+5)
LastIndexAnyUTF8/16:1-8      364ns ± 0%   158ns ± 0%     ~     (p=0.079 n=4+5)
LastIndexAnyUTF8/16:2-8      636ns ± 0%   472ns ± 0%  -25.79%  (p=0.000 n=5+4)
LastIndexAnyUTF8/16:4-8      630ns ± 0%   472ns ± 0%  -25.03%  (p=0.008 n=5+5)
LastIndexAnyUTF8/16:8-8     1.28µs ± 0%  0.47µs ± 0%  -63.09%  (p=0.016 n=5+4)
LastIndexAnyUTF8/16:16-8    1.66µs ± 0%  0.53µs ± 0%  -68.39%  (p=0.016 n=5+4)
LastIndexAnyUTF8/16:32-8    2.88µs ± 0%  0.53µs ± 0%  -81.72%  (p=0.008 n=5+5)
LastIndexAnyUTF8/16:64-8    5.08µs ± 0%  0.57µs ± 0%  -88.79%  (p=0.008 n=5+5)
LastIndexAnyUTF8/256:1-8    5.41µs ± 0%  2.03µs ± 0%  -62.46%  (p=0.016 n=4+5)
LastIndexAnyUTF8/256:2-8    9.77µs ± 0%  7.14µs ± 0%  -26.97%  (p=0.008 n=5+5)
LastIndexAnyUTF8/256:4-8    9.63µs ± 0%  7.14µs ± 0%  -25.86%  (p=0.008 n=5+5)
LastIndexAnyUTF8/256:8-8    20.0µs ± 0%   7.1µs ± 0%  -64.30%  (p=0.008 n=5+5)
LastIndexAnyUTF8/256:16-8   26.1µs ± 1%   8.0µs ± 0%  -69.40%  (p=0.008 n=5+5)
LastIndexAnyUTF8/256:32-8   45.6µs ± 1%   8.0µs ± 0%  -82.51%  (p=0.008 n=5+5)
LastIndexAnyUTF8/256:64-8   80.8µs ± 0%   8.6µs ± 0%  -89.33%  (p=0.016 n=5+4)
pkg:bytes goos:linux goarch:arm64
IndexAnyASCII/1:1-8         26.2ns ± 1%  26.5ns ± 0%   +1.30%  (p=0.016 n=5+4)
IndexAnyASCII/1:2-8         18.5ns ± 0%  26.5ns ± 0%  +43.24%  (p=0.008 n=5+5)
IndexAnyASCII/1:4-8         21.0ns ± 0%  26.5ns ± 0%  +26.38%  (p=0.008 n=5+5)
IndexAnyASCII/1:8-8         37.5ns ± 0%  26.5ns ± 0%  -29.33%  (p=0.000 n=5+4)
IndexAnyASCII/1:16-8        49.6ns ± 0%  26.5ns ± 0%  -46.49%  (p=0.008 n=5+5)
IndexAnyASCII/1:32-8        73.6ns ± 0%  30.1ns ± 0%  -59.16%  (p=0.008 n=5+5)
IndexAnyASCII/1:64-8         122ns ± 0%    33ns ± 0%  -73.23%  (p=0.008 n=5+5)
IndexAnyASCII/16:1-8        73.7ns ± 0%  33.4ns ± 0%  -54.71%  (p=0.008 n=5+5)
IndexAnyASCII/16:2-8        79.1ns ± 0%  78.9ns ± 0%   -0.30%  (p=0.016 n=4+5)
IndexAnyASCII/16:4-8        84.8ns ± 0%  86.1ns ± 0%   +1.58%  (p=0.016 n=5+4)
IndexAnyASCII/16:8-8         111ns ± 0%   111ns ± 0%     ~     (all equal)
IndexAnyASCII/16:16-8        139ns ± 0%   144ns ± 0%   +3.60%  (p=0.016 n=4+5)
IndexAnyASCII/16:32-8        196ns ± 0%   207ns ± 0%   +5.61%  (p=0.016 n=5+4)
IndexAnyASCII/16:64-8        311ns ± 0%   320ns ± 0%   +2.89%  (p=0.016 n=4+5)
IndexAnyASCII/256:1-8        674ns ± 0%    65ns ± 1%  -90.35%  (p=0.008 n=5+5)
IndexAnyASCII/256:2-8        680ns ± 0%   680ns ± 0%     ~     (p=0.444 n=5+5)
IndexAnyASCII/256:4-8        686ns ± 0%   687ns ± 0%     ~     (p=0.167 n=5+5)
IndexAnyASCII/256:8-8        713ns ± 0%   712ns ± 0%   -0.14%  (p=0.008 n=5+5)
IndexAnyASCII/256:16-8       740ns ± 0%   744ns ± 0%   +0.54%  (p=0.016 n=5+4)
IndexAnyASCII/256:32-8       797ns ± 0%   808ns ± 0%   +1.43%  (p=0.008 n=5+5)
IndexAnyASCII/256:64-8       912ns ± 0%   921ns ± 0%   +0.99%  (p=0.016 n=4+5)
IndexAnyUTF8/1:1-8          27.5ns ± 0%  26.5ns ± 0%   -3.64%  (p=0.008 n=5+5)
IndexAnyUTF8/1:2-8          44.5ns ± 0%  26.5ns ± 0%  -40.50%  (p=0.008 n=5+5)
IndexAnyUTF8/1:4-8          45.6ns ± 0%  26.5ns ± 0%  -41.89%  (p=0.000 n=5+4)
IndexAnyUTF8/1:8-8          85.8ns ± 1%  26.5ns ± 0%  -69.11%  (p=0.008 n=5+5)
IndexAnyUTF8/1:16-8          110ns ± 1%    26ns ± 0%  -76.00%  (p=0.016 n=5+4)
IndexAnyUTF8/1:32-8          188ns ± 0%    30ns ± 0%  -84.04%  (p=0.008 n=5+5)
IndexAnyUTF8/1:64-8          333ns ± 0%    33ns ± 0%  -90.20%  (p=0.008 n=5+5)
IndexAnyUTF8/16:1-8          294ns ± 0%   235ns ± 0%  -20.07%  (p=0.008 n=5+5)
IndexAnyUTF8/16:2-8          563ns ± 0%   309ns ± 0%  -45.12%  (p=0.008 n=5+5)
IndexAnyUTF8/16:4-8          558ns ± 1%   309ns ± 0%  -44.60%  (p=0.000 n=5+4)
IndexAnyUTF8/16:8-8         1.23µs ± 0%  0.31µs ± 0%  -74.79%  (p=0.008 n=5+5)
IndexAnyUTF8/16:16-8        1.62µs ± 2%  0.31µs ± 0%  -80.93%  (p=0.008 n=5+5)
IndexAnyUTF8/16:32-8        2.86µs ± 0%  0.38µs ± 0%  -86.87%  (p=0.008 n=5+5)
IndexAnyUTF8/16:64-8        5.18µs ± 0%  0.42µs ± 0%  -91.86%  (p=0.008 n=5+5)
IndexAnyUTF8/256:1-8        4.27µs ± 1%  3.30µs ± 1%  -22.75%  (p=0.008 n=5+5)
IndexAnyUTF8/256:2-8        8.61µs ± 0%  4.45µs ± 0%  -48.31%  (p=0.016 n=4+5)
IndexAnyUTF8/256:4-8        8.44µs ± 0%  4.45µs ± 0%  -47.23%  (p=0.008 n=5+5)
IndexAnyUTF8/256:8-8        19.2µs ± 0%   4.5µs ± 0%  -76.78%  (p=0.008 n=5+5)
IndexAnyUTF8/256:16-8       25.6µs ± 0%   4.5µs ± 0%  -82.63%  (p=0.008 n=5+5)
IndexAnyUTF8/256:32-8       45.4µs ± 0%   5.5µs ± 0%  -87.85%  (p=0.016 n=4+5)
IndexAnyUTF8/256:64-8       82.5µs ± 0%   6.2µs ± 0%  -92.49%  (p=0.008 n=5+5)
LastIndexAnyASCII/1:1-8     23.0ns ± 0%  26.5ns ± 0%  +15.02%  (p=0.008 n=5+5)
LastIndexAnyASCII/1:2-8     24.5ns ± 0%  26.5ns ± 0%   +8.16%  (p=0.008 n=5+5)
LastIndexAnyASCII/1:4-8     27.8ns ± 0%  26.5ns ± 0%   -4.68%  (p=0.029 n=4+4)
LastIndexAnyASCII/1:8-8     45.1ns ± 1%  26.5ns ± 0%  -41.29%  (p=0.000 n=5+4)
LastIndexAnyASCII/1:16-8    57.1ns ± 0%  26.5ns ± 0%  -53.61%  (p=0.008 n=5+5)
LastIndexAnyASCII/1:32-8    81.5ns ± 0%  30.0ns ± 0%     ~     (p=0.079 n=4+5)
LastIndexAnyASCII/1:64-8     129ns ± 0%    32ns ± 0%  -74.81%  (p=0.008 n=5+5)
LastIndexAnyASCII/16:1-8    72.6ns ± 0%  72.1ns ± 0%   -0.63%  (p=0.000 n=4+5)
LastIndexAnyASCII/16:2-8    77.2ns ± 0%  77.2ns ± 0%     ~     (p=0.167 n=5+5)
LastIndexAnyASCII/16:4-8    83.1ns ± 0%  83.2ns ± 0%     ~     (p=0.444 n=5+5)
LastIndexAnyASCII/16:8-8     109ns ± 1%   108ns ± 0%     ~     (p=0.167 n=5+5)
LastIndexAnyASCII/16:16-8    136ns ± 0%   136ns ± 0%     ~     (all equal)
LastIndexAnyASCII/16:32-8    195ns ± 0%   197ns ± 0%   +0.82%  (p=0.008 n=5+5)
LastIndexAnyASCII/16:64-8    309ns ± 0%   309ns ± 0%     ~     (all equal)
LastIndexAnyASCII/256:1-8    653ns ± 0%   657ns ± 0%   +0.61%  (p=0.008 n=5+5)
LastIndexAnyASCII/256:2-8    659ns ± 0%   658ns ± 0%     ~     (p=0.167 n=5+5)
LastIndexAnyASCII/256:4-8    664ns ± 0%   663ns ± 0%     ~     (p=0.095 n=5+4)
LastIndexAnyASCII/256:8-8    698ns ± 0%   689ns ± 0%   -1.29%  (p=0.008 n=5+5)
LastIndexAnyASCII/256:16-8   726ns ± 0%   717ns ± 0%   -1.24%  (p=0.008 n=5+5)
LastIndexAnyASCII/256:32-8   777ns ± 0%   779ns ± 0%     ~     (p=0.079 n=5+4)
LastIndexAnyASCII/256:64-8   889ns ± 0%   890ns ± 0%     ~     (p=0.444 n=5+5)
LastIndexAnyUTF8/1:1-8      32.1ns ± 0%  26.5ns ± 0%  -17.45%  (p=0.000 n=5+4)
LastIndexAnyUTF8/1:2-8      48.6ns ± 0%  26.5ns ± 0%  -45.52%  (p=0.000 n=5+4)
LastIndexAnyUTF8/1:4-8      49.6ns ± 0%  26.5ns ± 0%  -46.62%  (p=0.008 n=5+5)
LastIndexAnyUTF8/1:8-8      91.9ns ± 0%  26.5ns ± 0%  -71.18%  (p=0.008 n=5+5)
LastIndexAnyUTF8/1:16-8      114ns ± 1%    26ns ± 0%  -76.84%  (p=0.000 n=5+4)
LastIndexAnyUTF8/1:32-8      203ns ± 6%    30ns ± 0%  -85.25%  (p=0.008 n=5+5)
LastIndexAnyUTF8/1:64-8      330ns ± 0%    33ns ± 0%  -90.14%  (p=0.000 n=4+5)
LastIndexAnyUTF8/16:1-8      365ns ± 0%   164ns ± 0%  -55.04%  (p=0.008 n=5+5)
LastIndexAnyUTF8/16:2-8      638ns ± 0%   296ns ± 0%  -53.58%  (p=0.008 n=5+5)
LastIndexAnyUTF8/16:4-8      634ns ± 0%   296ns ± 0%  -53.31%  (p=0.008 n=5+5)
LastIndexAnyUTF8/16:8-8     1.30µs ± 0%  0.30µs ± 0%  -77.18%  (p=0.000 n=4+5)
LastIndexAnyUTF8/16:16-8    1.66µs ± 0%  0.30µs ± 0%  -82.19%  (p=0.008 n=5+5)
LastIndexAnyUTF8/16:32-8    2.90µs ± 0%  0.38µs ± 0%  -87.00%  (p=0.029 n=4+4)
LastIndexAnyUTF8/16:64-8    5.10µs ± 0%  0.42µs ± 0%  -91.78%  (p=0.008 n=5+5)
LastIndexAnyUTF8/256:1-8    5.42µs ± 0%  2.12µs ± 0%  -60.92%  (p=0.008 n=5+5)
LastIndexAnyUTF8/256:2-8    9.79µs ± 0%  4.26µs ± 0%  -56.47%  (p=0.008 n=5+5)
LastIndexAnyUTF8/256:4-8    9.66µs ± 0%  4.26µs ± 0%  -55.87%  (p=0.008 n=5+5)
LastIndexAnyUTF8/256:8-8    20.4µs ± 0%   4.3µs ± 0%  -79.10%  (p=0.008 n=5+5)
LastIndexAnyUTF8/256:16-8   26.0µs ± 1%   4.3µs ± 0%  -83.62%  (p=0.008 n=5+5)
LastIndexAnyUTF8/256:32-8   46.0µs ± 0%   5.5µs ± 0%  -88.09%  (p=0.008 n=5+5)
LastIndexAnyUTF8/256:64-8   81.1µs ± 0%   6.2µs ± 0%  -92.38%  (p=0.008 n=5+5)

name                         old time/op  new time/op   delta
pkg:strings goos:linux goarch:amd64
IndexAnyASCII/1:1-48         10.0ns ± 0%   13.3ns ± 0%  +33.00%  (p=0.008 n=5+5)
IndexAnyASCII/1:2-48         11.0ns ± 0%   15.5ns ± 0%  +40.55%  (p=0.016 n=4+5)
IndexAnyASCII/1:4-48         12.9ns ± 0%   15.4ns ± 0%  +19.69%  (p=0.008 n=5+5)
IndexAnyASCII/1:8-48         18.6ns ± 0%   15.5ns ± 0%  -16.45%  (p=0.000 n=4+5)
IndexAnyASCII/1:16-48        30.1ns ± 0%   16.9ns ± 0%     ~     (p=0.079 n=4+5)
IndexAnyASCII/1:32-48        53.1ns ± 0%   18.6ns ± 0%  -64.95%  (p=0.000 n=5+4)
IndexAnyASCII/1:64-48        98.9ns ± 0%   17.4ns ± 0%  -82.41%  (p=0.000 n=5+4)
IndexAnyASCII/16:1-48        35.0ns ± 0%   14.2ns ± 0%  -59.47%  (p=0.000 n=5+4)
IndexAnyASCII/16:2-48        35.5ns ± 0%   35.6ns ± 0%     ~     (p=0.238 n=5+4)
IndexAnyASCII/16:4-48        40.8ns ± 0%   40.7ns ± 1%     ~     (p=0.643 n=5+5)
IndexAnyASCII/16:8-48        50.8ns ± 0%   50.9ns ± 1%     ~     (p=1.000 n=4+5)
IndexAnyASCII/16:16-48       64.0ns ± 1%   64.5ns ± 1%     ~     (p=0.071 n=5+5)
IndexAnyASCII/16:32-48       98.3ns ± 0%  100.8ns ± 1%   +2.52%  (p=0.008 n=5+5)
IndexAnyASCII/16:64-48        156ns ± 0%    157ns ± 0%     ~     (p=0.238 n=4+5)
IndexAnyASCII/256:1-48        299ns ± 0%     24ns ± 3%  -92.12%  (p=0.008 n=5+5)
IndexAnyASCII/256:2-48        303ns ± 0%    304ns ± 0%     ~     (p=0.762 n=5+5)
IndexAnyASCII/256:4-48        311ns ± 0%    311ns ± 0%     ~     (p=0.476 n=5+5)
IndexAnyASCII/256:8-48        321ns ± 0%    321ns ± 0%     ~     (p=0.429 n=4+5)
IndexAnyASCII/256:16-48       334ns ± 0%    335ns ± 0%     ~     (p=0.079 n=5+4)
IndexAnyASCII/256:32-48       367ns ± 0%    365ns ± 0%     ~     (p=0.079 n=4+5)
IndexAnyASCII/256:64-48       431ns ± 1%    421ns ± 0%   -2.27%  (p=0.008 n=5+5)
IndexAnyUTF8/1:1-48          17.2ns ± 0%   10.8ns ± 0%  -37.21%  (p=0.029 n=4+4)
IndexAnyUTF8/1:2-48          26.7ns ± 0%   15.6ns ± 0%     ~     (p=0.079 n=4+5)
IndexAnyUTF8/1:4-48          28.2ns ± 0%   15.6ns ± 0%  -44.68%  (p=0.000 n=5+4)
IndexAnyUTF8/1:8-48          48.8ns ± 0%   15.6ns ± 0%  -68.03%  (p=0.029 n=4+4)
IndexAnyUTF8/1:16-48         58.3ns ± 0%   16.2ns ± 0%     ~     (p=0.079 n=4+5)
IndexAnyUTF8/1:32-48          103ns ± 0%     18ns ± 0%  -82.27%  (p=0.008 n=5+5)
IndexAnyUTF8/1:64-48          182ns ± 0%     17ns ± 0%  -90.53%  (p=0.008 n=5+5)
IndexAnyUTF8/16:1-48          197ns ± 0%     25ns ± 0%  -87.34%  (p=0.000 n=5+4)
IndexAnyUTF8/16:2-48          348ns ± 0%    163ns ± 0%  -53.11%  (p=0.000 n=5+4)
IndexAnyUTF8/16:4-48          374ns ± 0%    163ns ± 0%  -56.37%  (p=0.000 n=5+4)
IndexAnyUTF8/16:8-48          716ns ± 0%    163ns ± 0%  -77.22%  (p=0.000 n=5+4)
IndexAnyUTF8/16:16-48         859ns ± 0%    175ns ± 0%  -79.63%  (p=0.000 n=5+4)
IndexAnyUTF8/16:32-48        1.58µs ± 0%   0.20µs ± 0%  -87.01%  (p=0.029 n=4+4)
IndexAnyUTF8/16:64-48        2.84µs ± 0%   0.19µs ± 1%  -93.34%  (p=0.008 n=5+5)
IndexAnyUTF8/256:1-48        2.61µs ± 0%   0.27µs ± 0%  -89.81%  (p=0.008 n=5+5)
IndexAnyUTF8/256:2-48        4.95µs ± 0%   2.23µs ± 0%  -54.91%  (p=0.016 n=5+4)
IndexAnyUTF8/256:4-48        5.55µs ± 0%   2.23µs ± 0%  -59.72%  (p=0.008 n=5+5)
IndexAnyUTF8/256:8-48        10.8µs ± 0%    2.2µs ± 0%  -79.39%  (p=0.008 n=5+5)
IndexAnyUTF8/256:16-48       13.1µs ± 0%    2.5µs ± 0%  -81.21%  (p=0.016 n=4+5)
IndexAnyUTF8/256:32-48       24.7µs ± 0%    2.8µs ± 0%  -88.49%  (p=0.008 n=5+5)
IndexAnyUTF8/256:64-48       45.0µs ± 0%    2.6µs ± 1%  -94.23%  (p=0.008 n=5+5)
LastIndexAnyASCII/1:1-48     13.9ns ± 0%   15.2ns ± 0%   +9.35%  (p=0.008 n=5+5)
LastIndexAnyASCII/1:2-48     14.4ns ± 0%   15.2ns ± 0%   +5.56%  (p=0.008 n=5+5)
LastIndexAnyASCII/1:4-48     16.7ns ± 0%   15.2ns ± 0%   -8.98%  (p=0.008 n=5+5)
LastIndexAnyASCII/1:8-48     24.0ns ± 0%   15.2ns ± 0%  -36.67%  (p=0.008 n=5+5)
LastIndexAnyASCII/1:16-48    35.6ns ± 0%   15.0ns ± 0%  -57.82%  (p=0.008 n=5+5)
LastIndexAnyASCII/1:32-48    68.9ns ± 0%   16.7ns ± 0%  -75.75%  (p=0.008 n=5+5)
LastIndexAnyASCII/1:64-48     104ns ± 0%     17ns ± 1%  -83.81%  (p=0.008 n=5+5)
LastIndexAnyASCII/16:1-48    35.0ns ± 0%   35.0ns ± 0%     ~     (all equal)
LastIndexAnyASCII/16:2-48    35.6ns ± 0%   35.6ns ± 0%     ~     (all equal)
LastIndexAnyASCII/16:4-48    41.0ns ± 0%   40.8ns ± 0%   -0.49%  (p=0.032 n=5+5)
LastIndexAnyASCII/16:8-48    50.9ns ± 0%   50.7ns ± 1%     ~     (p=0.397 n=5+5)
LastIndexAnyASCII/16:16-48   64.3ns ± 1%   64.4ns ± 1%     ~     (p=1.000 n=4+5)
LastIndexAnyASCII/16:32-48    100ns ± 0%    100ns ± 0%   +0.38%  (p=0.016 n=4+5)
LastIndexAnyASCII/16:64-48    157ns ± 1%    163ns ± 0%   +3.82%  (p=0.008 n=5+5)
LastIndexAnyASCII/256:1-48    302ns ± 0%    300ns ± 0%   -0.53%  (p=0.008 n=5+5)
LastIndexAnyASCII/256:2-48    305ns ± 0%    303ns ± 0%   -0.66%  (p=0.000 n=5+4)
LastIndexAnyASCII/256:4-48    313ns ± 0%    307ns ± 0%   -2.04%  (p=0.000 n=4+5)
LastIndexAnyASCII/256:8-48    323ns ± 0%    315ns ± 0%   -2.48%  (p=0.029 n=4+4)
LastIndexAnyASCII/256:16-48   333ns ± 0%    332ns ± 0%   -0.30%  (p=0.048 n=5+5)
LastIndexAnyASCII/256:32-48   366ns ± 0%    367ns ± 0%     ~     (p=0.238 n=4+5)
LastIndexAnyASCII/256:64-48   430ns ± 0%    430ns ± 0%     ~     (p=1.000 n=5+5)
LastIndexAnyUTF8/1:1-48      21.1ns ± 0%   13.9ns ± 0%  -34.00%  (p=0.008 n=5+5)
LastIndexAnyUTF8/1:2-48      29.5ns ± 0%   13.9ns ± 0%  -52.95%  (p=0.008 n=5+5)
LastIndexAnyUTF8/1:4-48      31.6ns ± 0%   13.9ns ± 0%  -55.96%  (p=0.008 n=5+5)
LastIndexAnyUTF8/1:8-48      51.1ns ± 0%   13.9ns ± 0%  -72.81%  (p=0.008 n=5+5)
LastIndexAnyUTF8/1:16-48     58.9ns ± 0%   14.6ns ± 0%  -75.23%  (p=0.016 n=5+4)
LastIndexAnyUTF8/1:32-48      103ns ± 0%     16ns ± 1%  -84.12%  (p=0.008 n=5+5)
LastIndexAnyUTF8/1:64-48      177ns ± 0%     17ns ± 1%  -90.62%  (p=0.008 n=5+5)
LastIndexAnyUTF8/16:1-48      275ns ± 1%    105ns ± 0%  -61.85%  (p=0.000 n=5+4)
LastIndexAnyUTF8/16:2-48      406ns ± 0%    216ns ± 0%  -46.70%  (p=0.008 n=5+5)
LastIndexAnyUTF8/16:4-48      458ns ± 0%    216ns ± 0%  -52.75%  (p=0.000 n=4+5)
LastIndexAnyUTF8/16:8-48      753ns ± 0%    216ns ± 0%  -71.31%  (p=0.029 n=4+4)
LastIndexAnyUTF8/16:16-48     902ns ± 0%    221ns ± 0%  -75.50%  (p=0.016 n=5+4)
LastIndexAnyUTF8/16:32-48    1.57µs ± 0%   0.24µs ± 0%  -84.46%  (p=0.008 n=5+5)
LastIndexAnyUTF8/16:64-48    2.77µs ± 0%   0.24µs ± 0%  -91.22%  (p=0.000 n=5+4)
LastIndexAnyUTF8/256:1-48    4.06µs ± 0%   1.53µs ± 0%  -62.26%  (p=0.008 n=5+5)
LastIndexAnyUTF8/256:2-48    5.92µs ± 0%   3.04µs ± 0%  -48.55%  (p=0.016 n=4+5)
LastIndexAnyUTF8/256:4-48    6.82µs ± 0%   3.04µs ± 0%  -55.34%  (p=0.008 n=5+5)
LastIndexAnyUTF8/256:8-48    11.5µs ± 0%    3.0µs ± 0%  -73.48%  (p=0.008 n=5+5)
LastIndexAnyUTF8/256:16-48   14.1µs ± 0%    3.1µs ± 0%  -77.85%  (p=0.008 n=5+5)
LastIndexAnyUTF8/256:32-48   24.5µs ± 0%    3.5µs ± 0%  -85.85%  (p=0.016 n=5+4)
LastIndexAnyUTF8/256:64-48   44.0µs ± 0%    3.5µs ± 0%  -92.12%  (p=0.008 n=5+5)
pkg:bytes goos:linux goarch:amd64
IndexAnyASCII/1:1-48         9.56ns ± 0%  11.00ns ± 0%  +15.06%  (p=0.016 n=5+4)
IndexAnyASCII/1:2-48         11.0ns ± 0%   10.8ns ± 2%   -1.64%  (p=0.048 n=5+5)
IndexAnyASCII/1:4-48         13.9ns ± 0%   11.0ns ± 1%  -21.15%  (p=0.008 n=5+5)
IndexAnyASCII/1:8-48         19.6ns ± 0%   10.8ns ± 3%  -44.90%  (p=0.008 n=5+5)
IndexAnyASCII/1:16-48        31.1ns ± 0%   11.5ns ± 0%  -63.02%  (p=0.008 n=5+5)
IndexAnyASCII/1:32-48        54.0ns ± 0%   11.8ns ± 0%  -78.15%  (p=0.000 n=5+4)
IndexAnyASCII/1:64-48         100ns ± 0%     13ns ± 0%  -86.89%  (p=0.008 n=5+5)
IndexAnyASCII/16:1-48        35.5ns ± 0%   14.8ns ± 0%  -58.26%  (p=0.008 n=5+5)
IndexAnyASCII/16:2-48        36.2ns ± 1%   36.0ns ± 1%     ~     (p=0.087 n=5+5)
IndexAnyASCII/16:4-48        40.3ns ± 1%   39.7ns ± 4%     ~     (p=0.175 n=4+5)
IndexAnyASCII/16:8-48        48.7ns ± 5%   45.8ns ± 0%   -6.02%  (p=0.016 n=5+4)
IndexAnyASCII/16:16-48       64.1ns ±11%   62.1ns ± 1%     ~     (p=0.143 n=5+5)
IndexAnyASCII/16:32-48       97.9ns ± 1%   98.3ns ± 1%     ~     (p=0.294 n=5+5)
IndexAnyASCII/16:64-48        163ns ± 0%    157ns ± 0%   -3.68%  (p=0.008 n=5+5)
IndexAnyASCII/256:1-48        389ns ± 0%     25ns ± 0%  -93.65%  (p=0.000 n=5+4)
IndexAnyASCII/256:2-48        391ns ± 0%    307ns ± 0%  -21.48%  (p=0.000 n=5+4)
IndexAnyASCII/256:4-48        394ns ± 0%    323ns ± 0%  -17.92%  (p=0.008 n=5+5)
IndexAnyASCII/256:8-48        402ns ± 0%    323ns ± 0%  -19.51%  (p=0.008 n=5+5)
IndexAnyASCII/256:16-48       414ns ± 0%    334ns ± 0%  -19.32%  (p=0.016 n=4+5)
IndexAnyASCII/256:32-48       446ns ± 0%    367ns ± 0%  -17.75%  (p=0.016 n=5+4)
IndexAnyASCII/256:64-48       511ns ± 0%    424ns ± 0%  -17.02%  (p=0.008 n=5+5)
IndexAnyUTF8/1:1-48          17.4ns ± 0%   11.0ns ± 0%  -36.64%  (p=0.008 n=5+5)
IndexAnyUTF8/1:2-48          27.3ns ± 1%   11.0ns ± 0%  -59.74%  (p=0.008 n=5+5)
IndexAnyUTF8/1:4-48          28.7ns ± 0%   11.0ns ± 0%  -61.73%  (p=0.008 n=5+5)
IndexAnyUTF8/1:8-48          49.2ns ± 0%   11.0ns ± 0%  -77.66%  (p=0.008 n=5+5)
IndexAnyUTF8/1:16-48         56.0ns ± 0%   11.5ns ± 0%  -79.46%  (p=0.000 n=5+4)
IndexAnyUTF8/1:32-48          102ns ± 0%     12ns ± 0%  -88.24%  (p=0.008 n=5+5)
IndexAnyUTF8/1:64-48          177ns ± 0%     13ns ± 0%  -92.51%  (p=0.008 n=5+5)
IndexAnyUTF8/16:1-48          212ns ± 0%    112ns ± 0%  -47.17%  (p=0.008 n=5+5)
IndexAnyUTF8/16:2-48          356ns ± 0%    159ns ± 1%  -55.28%  (p=0.000 n=4+5)
IndexAnyUTF8/16:4-48          372ns ± 0%    158ns ± 0%  -57.47%  (p=0.008 n=5+5)
IndexAnyUTF8/16:8-48          712ns ± 0%    159ns ± 1%  -77.70%  (p=0.008 n=5+5)
IndexAnyUTF8/16:16-48         829ns ± 0%    129ns ± 0%  -84.44%  (p=0.008 n=5+5)
IndexAnyUTF8/16:32-48        1.55µs ± 0%   0.16µs ± 0%  -89.87%  (p=0.008 n=5+5)
IndexAnyUTF8/16:64-48        2.77µs ± 0%   0.14µs ± 0%  -94.94%  (p=0.008 n=5+5)
IndexAnyUTF8/256:1-48        2.85µs ± 0%   1.63µs ± 1%  -42.74%  (p=0.008 n=5+5)
IndexAnyUTF8/256:2-48        5.14µs ± 1%   2.03µs ± 0%  -60.51%  (p=0.008 n=5+5)
IndexAnyUTF8/256:4-48        5.56µs ± 0%   2.03µs ± 0%  -63.52%  (p=0.008 n=5+5)
IndexAnyUTF8/256:8-48        10.8µs ± 0%    2.0µs ± 0%  -81.22%  (p=0.008 n=5+5)
IndexAnyUTF8/256:16-48       12.9µs ± 0%    1.9µs ± 0%  -85.55%  (p=0.008 n=5+5)
IndexAnyUTF8/256:32-48       24.2µs ± 0%    2.1µs ± 0%  -91.29%  (p=0.016 n=5+4)
IndexAnyUTF8/256:64-48       43.7µs ± 0%    2.0µs ± 0%  -95.32%  (p=0.016 n=5+4)
LastIndexAnyASCII/1:1-48     13.7ns ± 1%   12.8ns ± 0%   -6.57%  (p=0.016 n=5+4)
LastIndexAnyASCII/1:2-48     14.7ns ± 0%   12.7ns ± 1%  -13.33%  (p=0.000 n=4+5)
LastIndexAnyASCII/1:4-48     16.9ns ± 0%   12.7ns ± 1%  -24.73%  (p=0.000 n=4+5)
LastIndexAnyASCII/1:8-48     20.5ns ± 0%   12.7ns ± 0%  -37.85%  (p=0.000 n=4+5)
LastIndexAnyASCII/1:16-48    28.0ns ± 0%   11.7ns ± 0%     ~     (p=0.079 n=4+5)
LastIndexAnyASCII/1:32-48    69.8ns ± 0%   12.4ns ± 0%  -82.19%  (p=0.008 n=5+5)
LastIndexAnyASCII/1:64-48    73.8ns ± 0%   13.3ns ± 0%  -82.03%  (p=0.000 n=4+5)
LastIndexAnyASCII/16:1-48    35.5ns ± 0%   35.5ns ± 0%     ~     (all equal)
LastIndexAnyASCII/16:2-48    36.0ns ± 0%   36.1ns ± 0%   +0.28%  (p=0.016 n=4+5)
LastIndexAnyASCII/16:4-48    40.3ns ± 2%   40.0ns ± 6%     ~     (p=0.651 n=5+5)
LastIndexAnyASCII/16:8-48    50.3ns ± 0%   50.2ns ± 9%     ~     (p=0.175 n=4+5)
LastIndexAnyASCII/16:16-48   62.4ns ± 4%   64.4ns ± 0%   +3.28%  (p=0.016 n=5+4)
LastIndexAnyASCII/16:32-48   98.9ns ± 0%   98.4ns ± 0%   -0.53%  (p=0.016 n=5+4)
LastIndexAnyASCII/16:64-48    160ns ± 1%    161ns ± 1%     ~     (p=0.325 n=5+5)
LastIndexAnyASCII/256:1-48    300ns ± 0%    301ns ± 0%   +0.33%  (p=0.008 n=5+5)
LastIndexAnyASCII/256:2-48    304ns ± 0%    304ns ± 0%     ~     (p=1.000 n=5+5)
LastIndexAnyASCII/256:4-48    311ns ± 0%    311ns ± 0%     ~     (p=0.556 n=4+5)
LastIndexAnyASCII/256:8-48    320ns ± 0%    321ns ± 0%     ~     (p=0.143 n=5+5)
LastIndexAnyASCII/256:16-48   333ns ± 0%    335ns ± 0%   +0.60%  (p=0.029 n=4+4)
LastIndexAnyASCII/256:32-48   367ns ± 0%    366ns ± 0%     ~     (p=0.095 n=4+5)
LastIndexAnyASCII/256:64-48   431ns ± 0%    424ns ± 0%   -1.62%  (p=0.008 n=5+5)
LastIndexAnyUTF8/1:1-48      19.7ns ± 1%   11.9ns ± 0%  -39.47%  (p=0.008 n=5+5)
LastIndexAnyUTF8/1:2-48      27.6ns ± 1%   11.9ns ± 0%  -56.82%  (p=0.008 n=5+5)
LastIndexAnyUTF8/1:4-48      29.9ns ± 0%   11.9ns ± 0%     ~     (p=0.079 n=4+5)
LastIndexAnyUTF8/1:8-48      48.7ns ± 0%   11.9ns ± 0%  -75.54%  (p=0.008 n=5+5)
LastIndexAnyUTF8/1:16-48     57.8ns ± 0%   11.4ns ± 0%  -80.26%  (p=0.008 n=5+5)
LastIndexAnyUTF8/1:32-48     94.7ns ± 0%   12.2ns ± 0%  -87.07%  (p=0.008 n=5+5)
LastIndexAnyUTF8/1:64-48      163ns ± 0%     13ns ± 1%  -91.93%  (p=0.008 n=5+5)
LastIndexAnyUTF8/16:1-48      258ns ± 0%     88ns ± 0%  -65.76%  (p=0.008 n=5+5)
LastIndexAnyUTF8/16:2-48      400ns ± 0%    162ns ± 0%  -59.38%  (p=0.008 n=5+5)
LastIndexAnyUTF8/16:4-48      415ns ± 0%    162ns ± 0%  -60.87%  (p=0.008 n=5+5)
LastIndexAnyUTF8/16:8-48      737ns ± 0%    162ns ± 0%  -78.02%  (p=0.000 n=5+4)
LastIndexAnyUTF8/16:16-48     882ns ± 0%    128ns ± 0%  -85.49%  (p=0.008 n=5+5)
LastIndexAnyUTF8/16:32-48    1.47µs ± 0%   0.16µs ± 0%  -89.29%  (p=0.000 n=4+5)
LastIndexAnyUTF8/16:64-48    2.56µs ± 0%   0.14µs ± 0%  -94.41%  (p=0.016 n=5+4)
LastIndexAnyUTF8/256:1-48    3.60µs ± 0%   1.23µs ± 0%  -65.67%  (p=0.008 n=5+5)
LastIndexAnyUTF8/256:2-48    5.78µs ± 0%   2.18µs ± 0%  -62.32%  (p=0.008 n=5+5)
LastIndexAnyUTF8/256:4-48    6.26µs ± 0%   2.18µs ± 0%  -65.15%  (p=0.008 n=5+5)
LastIndexAnyUTF8/256:8-48    11.2µs ± 0%    2.2µs ± 0%  -80.53%  (p=0.008 n=5+5)
LastIndexAnyUTF8/256:16-48   13.5µs ± 0%    1.9µs ± 0%  -86.02%  (p=0.016 n=4+5)
LastIndexAnyUTF8/256:32-48   23.0µs ± 0%    2.1µs ± 0%  -90.72%  (p=0.008 n=5+5)
LastIndexAnyUTF8/256:64-48   40.5µs ± 0%    2.1µs ± 0%  -94.73%  (p=0.008 n=5+5)

Change-Id: Ie05e306f8b184b989701868cb161ce8b3f18203b
Reviewed-on: https://go-review.googlesource.com/c/go/+/156998
Run-TryBot: eric fang <eric.fang@arm.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

2 files changed, 86 insertions, 12 deletions

diff --git a/src/strings/strings.go b/src/strings/strings.go
index 7fb05b7d0e..2789f5fb25 100644
--- a/src/strings/strings.go
+++ b/src/strings/strings.go
@@ -143,6 +143,14 @@ func IndexAny(s, chars string) int {
 		// Avoid scanning all of s.
 		return -1
 	}
+	if len(chars) == 1 {
+		// Avoid scanning all of s.
+		r := rune(chars[0])
+		if r >= utf8.RuneSelf {
+			r = utf8.RuneError
+		}
+		return IndexRune(s, r)
+	}
 	if len(s) > 8 {
 		if as, isASCII := makeASCIISet(chars); isASCII {
 			for i := 0; i < len(s); i++ {
@@ -154,10 +162,8 @@ func IndexAny(s, chars string) int {
 		}
 	}
 	for i, c := range s {
-		for _, m := range chars {
-			if c == m {
-				return i
-			}
+		if IndexRune(chars, c) >= 0 {
+			return i
 		}
 	}
 	return -1
@@ -171,6 +177,16 @@ func LastIndexAny(s, chars string) int {
 		// Avoid scanning all of s.
 		return -1
 	}
+	if len(s) == 1 {
+		rc := rune(s[0])
+		if rc >= utf8.RuneSelf {
+			rc = utf8.RuneError
+		}
+		if IndexRune(chars, rc) >= 0 {
+			return 0
+		}
+		return -1
+	}
 	if len(s) > 8 {
 		if as, isASCII := makeASCIISet(chars); isASCII {
 			for i := len(s) - 1; i >= 0; i-- {
@@ -181,13 +197,25 @@ func LastIndexAny(s, chars string) int {
 			return -1
 		}
 	}
+	if len(chars) == 1 {
+		rc := rune(chars[0])
+		if rc >= utf8.RuneSelf {
+			rc = utf8.RuneError
+		}
+		for i := len(s); i > 0; {
+			r, size := utf8.DecodeLastRuneInString(s[:i])
+			i -= size
+			if rc == r {
+				return i
+			}
+		}
+		return -1
+	}
 	for i := len(s); i > 0; {
 		r, size := utf8.DecodeLastRuneInString(s[:i])
 		i -= size
-		for _, c := range chars {
-			if r == c {
-				return i
-			}
+		if IndexRune(chars, r) >= 0 {
+			return i
 		}
 	}
 	return -1
diff --git a/src/strings/strings_test.go b/src/strings/strings_test.go
index 984fecfa8d..c01c4dabc5 100644
--- a/src/strings/strings_test.go
+++ b/src/strings/strings_test.go
@@ -153,6 +153,7 @@ var indexAnyTests = []IndexTest{
 	{"", "abc", -1},
 	{"a", "", -1},
 	{"a", "a", 0},
+	{"\x80", "\xffb", 0},
 	{"aaa", "a", 0},
 	{"abc", "xyz", -1},
 	{"abc", "xcz", 2},
@@ -163,6 +164,7 @@ var indexAnyTests = []IndexTest{
 	{dots + dots + dots, " ", -1},
 	{"012abcba210", "\xffb", 4},
 	{"012\x80bcb\x80210", "\xffb", 3},
+	{"0123456\xcf\x80abc", "\xcfb\x80", 10},
 }
 
 var lastIndexAnyTests = []IndexTest{
@@ -171,6 +173,7 @@ var lastIndexAnyTests = []IndexTest{
 	{"", "abc", -1},
 	{"a", "", -1},
 	{"a", "a", 0},
+	{"\x80", "\xffb", 0},
 	{"aaa", "a", 2},
 	{"abc", "xyz", -1},
 	{"abc", "ab", 1},
@@ -181,6 +184,7 @@ var lastIndexAnyTests = []IndexTest{
 	{dots + dots + dots, " ", -1},
 	{"012abcba210", "\xffb", 6},
 	{"012\x80bcb\x80210", "\xffb", 7},
+	{"0123456\xcf\x80abc", "\xcfb\x80", 10},
 }
 
 // Execute f on each test case.  funcName should be the name of f; it's used
@@ -1787,10 +1791,24 @@ func BenchmarkRepeat(b *testing.B) {
 }
 
 func BenchmarkIndexAnyASCII(b *testing.B) {
-	x := Repeat("#", 4096) // Never matches set
-	cs := "0123456789abcdef"
-	for k := 1; k <= 4096; k <<= 4 {
-		for j := 1; j <= 16; j <<= 1 {
+	x := Repeat("#", 2048) // Never matches set
+	cs := "0123456789abcdefghijklmnopqrstuvwxyz0123456789abcdefghijklmnopqrstuvwxyz"
+	for k := 1; k <= 2048; k <<= 4 {
+		for j := 1; j <= 64; j <<= 1 {
+			b.Run(fmt.Sprintf("%d:%d", k, j), func(b *testing.B) {
+				for i := 0; i < b.N; i++ {
+					IndexAny(x[:k], cs[:j])
+				}
+			})
+		}
+	}
+}
+
+func BenchmarkIndexAnyUTF8(b *testing.B) {
+	x := Repeat("#", 2048) // Never matches set
+	cs := "你好世界, hello world. 你好世界, hello world. 你好世界, hello world."
+	for k := 1; k <= 2048; k <<= 4 {
+		for j := 1; j <= 64; j <<= 1 {
 			b.Run(fmt.Sprintf("%d:%d", k, j), func(b *testing.B) {
 				for i := 0; i < b.N; i++ {
 					IndexAny(x[:k], cs[:j])
@@ -1800,6 +1818,34 @@ func BenchmarkIndexAnyASCII(b *testing.B) {
 	}
 }
 
+func BenchmarkLastIndexAnyASCII(b *testing.B) {
+	x := Repeat("#", 2048) // Never matches set
+	cs := "0123456789abcdefghijklmnopqrstuvwxyz0123456789abcdefghijklmnopqrstuvwxyz"
+	for k := 1; k <= 2048; k <<= 4 {
+		for j := 1; j <= 64; j <<= 1 {
+			b.Run(fmt.Sprintf("%d:%d", k, j), func(b *testing.B) {
+				for i := 0; i < b.N; i++ {
+					LastIndexAny(x[:k], cs[:j])
+				}
+			})
+		}
+	}
+}
+
+func BenchmarkLastIndexAnyUTF8(b *testing.B) {
+	x := Repeat("#", 2048) // Never matches set
+	cs := "你好世界, hello world. 你好世界, hello world. 你好世界, hello world."
+	for k := 1; k <= 2048; k <<= 4 {
+		for j := 1; j <= 64; j <<= 1 {
+			b.Run(fmt.Sprintf("%d:%d", k, j), func(b *testing.B) {
+				for i := 0; i < b.N; i++ {
+					LastIndexAny(x[:k], cs[:j])
+				}
+			})
+		}
+	}
+}
+
 func BenchmarkTrimASCII(b *testing.B) {
 	cs := "0123456789abcdef"
 	for k := 1; k <= 4096; k <<= 4 {