[LANG-1588] performance refine for StringUtils.center

[XenoAmess]

as title.

[coveralls]

Coverage increased (+0.002%) to 94.959% when pulling 31a1989 on xenoamess-fork:refine_center into e233ab6 on apache:master.

[garydgregory]

I do not understand what this PR is about and you'd be correct in assuming that I did not parse out the new code in my head or run it in the debugger. What are you "refining" here? If you change the algorithm, please use the commit comment to explain why implementing this method in this manner is better. The commit comment and code comment are only way for anyone looking at the code and commit log to make sense of what your intent it is and why it happened. TY.

[XenoAmess]

@garydgregory
This pr is a performance refine pr.
I add some jmh test for this pr after you asking it.

[XenoAmess]

jmh result:

[INFO] --- exec-maven-plugin:1.6.0:exec (benchmark) @ commons-lang3 ---
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.openjdk.jmh.util.Utils (file:/C:/Users/xenoa/.m2/repository/org/openjdk/jmh/jmh-core/1
.21/jmh-core-1.21.jar) to field java.io.PrintStream.charOut
WARNING: Please consider reporting this to the maintainers of org.openjdk.jmh.util.Utils
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
# JMH version: 1.21
# VM version: JDK 13.0.2, OpenJDK 64-Bit Server VM, 13.0.2+8
# VM invoker: C:\jdk-13.0.2+8\bin\java.exe
# VM options: <none>
# Warmup: 5 iterations, 10 s each
# Measurement: 5 iterations, 10 s each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: org.apache.commons.lang3.StringUtilCenterTest.test0New

# Run progress: 0.00% complete, ETA 00:33:20
# Fork: 1 of 5
# Warmup Iteration   1: 73.970 ns/op
# Warmup Iteration   2: 69.102 ns/op
# Warmup Iteration   3: 69.798 ns/op
# Warmup Iteration   4: 66.163 ns/op
# Warmup Iteration   5: 63.440 ns/op
Iteration   1: 64.715 ns/op
Iteration   2: 64.716 ns/op
Iteration   3: 74.180 ns/op
Iteration   4: 72.618 ns/op
Iteration   5: 75.182 ns/op

# Run progress: 5.00% complete, ETA 00:31:54
# Fork: 2 of 5
# Warmup Iteration   1: 67.586 ns/op
# Warmup Iteration   2: 65.819 ns/op
# Warmup Iteration   3: 63.447 ns/op
# Warmup Iteration   4: 65.497 ns/op
# Warmup Iteration   5: 63.994 ns/op
Iteration   1: 63.189 ns/op
Iteration   2: 65.755 ns/op
Iteration   3: 65.839 ns/op
Iteration   4: 65.091 ns/op
Iteration   5: 63.715 ns/op

# Run progress: 10.00% complete, ETA 00:30:12
# Fork: 3 of 5
# Warmup Iteration   1: 64.871 ns/op
# Warmup Iteration   2: 65.010 ns/op
# Warmup Iteration   3: 65.238 ns/op
# Warmup Iteration   4: 63.760 ns/op
# Warmup Iteration   5: 64.467 ns/op
Iteration   1: 65.498 ns/op
Iteration   2: 64.989 ns/op
Iteration   3: 70.976 ns/op
Iteration   4: 66.951 ns/op
Iteration   5: 67.054 ns/op

# Run progress: 15.00% complete, ETA 00:28:31
# Fork: 4 of 5
# Warmup Iteration   1: 66.880 ns/op
# Warmup Iteration   2: 64.242 ns/op
# Warmup Iteration   3: 64.745 ns/op
# Warmup Iteration   4: 64.326 ns/op
# Warmup Iteration   5: 64.886 ns/op
Iteration   1: 63.967 ns/op
Iteration   2: 63.959 ns/op
Iteration   3: 65.041 ns/op
Iteration   4: 63.518 ns/op
Iteration   5: 64.119 ns/op

# Run progress: 20.00% complete, ETA 00:26:50
# Fork: 5 of 5
# Warmup Iteration   1: 74.978 ns/op
# Warmup Iteration   2: 73.869 ns/op
# Warmup Iteration   3: 70.176 ns/op
# Warmup Iteration   4: 64.718 ns/op
# Warmup Iteration   5: 62.849 ns/op
Iteration   1: 63.283 ns/op
Iteration   2: 63.399 ns/op
Iteration   3: 64.567 ns/op
Iteration   4: 61.981 ns/op
Iteration   5: 63.795 ns/op


Result "org.apache.commons.lang3.StringUtilCenterTest.test0New":
  65.924 ?99.9%) 2.632 ns/op [Average]

  (min, avg, max) = (61.981, 65.924, 75.182), stdev = 3.514
  CI (99.9%): [63.291, 68.556] (assumes normal distribution)


# JMH version: 1.21
# VM version: JDK 13.0.2, OpenJDK 64-Bit Server VM, 13.0.2+8
# VM invoker: C:\jdk-13.0.2+8\bin\java.exe
# VM options: <none>
# Warmup: 5 iterations, 10 s each
# Measurement: 5 iterations, 10 s each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: org.apache.commons.lang3.StringUtilCenterTest.test0Old

# Run progress: 25.00% complete, ETA 00:25:09
# Fork: 1 of 5
# Warmup Iteration   1: 67.660 ns/op
# Warmup Iteration   2: 64.947 ns/op
# Warmup Iteration   3: 64.171 ns/op
# Warmup Iteration   4: 63.782 ns/op
# Warmup Iteration   5: 63.521 ns/op
Iteration   1: 64.632 ns/op
Iteration   2: 63.704 ns/op
Iteration   3: 63.486 ns/op
Iteration   4: 64.546 ns/op
Iteration   5: 64.219 ns/op

# Run progress: 30.00% complete, ETA 00:23:29
# Fork: 2 of 5
# Warmup Iteration   1: 68.962 ns/op
# Warmup Iteration   2: 64.948 ns/op
# Warmup Iteration   3: 63.874 ns/op
# Warmup Iteration   4: 66.906 ns/op
# Warmup Iteration   5: 66.031 ns/op
Iteration   1: 65.594 ns/op
Iteration   2: 70.326 ns/op
Iteration   3: 66.059 ns/op
Iteration   4: 65.465 ns/op
Iteration   5: 63.751 ns/op

# Run progress: 35.00% complete, ETA 00:21:48
# Fork: 3 of 5
# Warmup Iteration   1: 75.793 ns/op
# Warmup Iteration   2: 71.874 ns/op
# Warmup Iteration   3: 76.445 ns/op
# Warmup Iteration   4: 80.507 ns/op
# Warmup Iteration   5: 80.730 ns/op
Iteration   1: 75.477 ns/op
Iteration   2: 72.640 ns/op
Iteration   3: 86.545 ns/op
Iteration   4: 72.018 ns/op
Iteration   5: 72.236 ns/op

# Run progress: 40.00% complete, ETA 00:20:07
# Fork: 4 of 5
# Warmup Iteration   1: 67.321 ns/op
# Warmup Iteration   2: 65.013 ns/op
# Warmup Iteration   3: 64.822 ns/op
# Warmup Iteration   4: 64.609 ns/op
# Warmup Iteration   5: 64.005 ns/op
Iteration   1: 64.883 ns/op
Iteration   2: 63.384 ns/op
Iteration   3: 64.585 ns/op
Iteration   4: 65.865 ns/op
Iteration   5: 65.136 ns/op

# Run progress: 45.00% complete, ETA 00:18:27
# Fork: 5 of 5
# Warmup Iteration   1: 72.468 ns/op
# Warmup Iteration   2: 71.567 ns/op
# Warmup Iteration   3: 70.487 ns/op
# Warmup Iteration   4: 69.775 ns/op
# Warmup Iteration   5: 72.405 ns/op
Iteration   1: 69.492 ns/op
Iteration   2: 70.049 ns/op
Iteration   3: 70.439 ns/op
Iteration   4: 70.214 ns/op
Iteration   5: 69.640 ns/op


Result "org.apache.commons.lang3.StringUtilCenterTest.test0Old":
  68.175 ?99.9%) 3.886 ns/op [Average]

  (min, avg, max) = (63.384, 68.175, 86.545), stdev = 5.188
  CI (99.9%): [64.289, 72.061] (assumes normal distribution)


# JMH version: 1.21
# VM version: JDK 13.0.2, OpenJDK 64-Bit Server VM, 13.0.2+8
# VM invoker: C:\jdk-13.0.2+8\bin\java.exe
# VM options: <none>
# Warmup: 5 iterations, 10 s each
# Measurement: 5 iterations, 10 s each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: org.apache.commons.lang3.StringUtilCenterTest.test1New

# Run progress: 50.00% complete, ETA 00:16:46
# Fork: 1 of 5
# Warmup Iteration   1: 26326250.789 ns/op
# Warmup Iteration   2: 25239957.683 ns/op
# Warmup Iteration   3: 25217874.811 ns/op
# Warmup Iteration   4: 29799395.536 ns/op
# Warmup Iteration   5: 25481418.575 ns/op
Iteration   1: 27424505.205 ns/op
Iteration   2: 32866042.295 ns/op
Iteration   3: 25211274.811 ns/op
Iteration   4: 26647165.957 ns/op
Iteration   5: 28455071.023 ns/op

# Run progress: 55.00% complete, ETA 00:15:06
# Fork: 2 of 5
# Warmup Iteration   1: 27791962.222 ns/op
# Warmup Iteration   2: 25545446.173 ns/op
# Warmup Iteration   3: 25595086.701 ns/op
# Warmup Iteration   4: 29474667.353 ns/op
# Warmup Iteration   5: 23791697.150 ns/op
Iteration   1: 25600432.481 ns/op
Iteration   2: 28094228.933 ns/op
Iteration   3: 21998013.187 ns/op
Iteration   4: 30368663.333 ns/op
Iteration   5: 24707792.840 ns/op

# Run progress: 60.00% complete, ETA 00:13:26
# Fork: 3 of 5
# Warmup Iteration   1: 26658096.809 ns/op
# Warmup Iteration   2: 25738426.992 ns/op
# Warmup Iteration   3: 25444187.310 ns/op
# Warmup Iteration   4: 29603887.870 ns/op
# Warmup Iteration   5: 23952392.823 ns/op
Iteration   1: 26057157.813 ns/op
Iteration   2: 29099787.791 ns/op
Iteration   3: 22069017.621 ns/op
Iteration   4: 28992393.623 ns/op
Iteration   5: 25628914.066 ns/op

# Run progress: 65.00% complete, ETA 00:11:45
# Fork: 4 of 5
# Warmup Iteration   1: 26624345.745 ns/op
# Warmup Iteration   2: 25712105.141 ns/op
# Warmup Iteration   3: 25732705.913 ns/op
# Warmup Iteration   4: 29031242.609 ns/op
# Warmup Iteration   5: 23822108.571 ns/op
Iteration   1: 26038135.065 ns/op
Iteration   2: 28183252.958 ns/op
Iteration   3: 23823259.286 ns/op
Iteration   4: 33591714.094 ns/op
Iteration   5: 33456041.806 ns/op

# Run progress: 70.00% complete, ETA 00:10:05
# Fork: 5 of 5
# Warmup Iteration   1: 29365897.947 ns/op
# Warmup Iteration   2: 27275929.700 ns/op
# Warmup Iteration   3: 28926793.642 ns/op
# Warmup Iteration   4: 29033741.739 ns/op
# Warmup Iteration   5: 23825106.905 ns/op
Iteration   1: 32482081.818 ns/op
Iteration   2: 26602738.830 ns/op
Iteration   3: 25330494.697 ns/op
Iteration   4: 31557474.448 ns/op
Iteration   5: 25133722.613 ns/op


Result "org.apache.commons.lang3.StringUtilCenterTest.test1New":
  27576775.064 ?99.9%) 2497347.881 ns/op [Average]

  (min, avg, max) = (21998013.187, 27576775.064, 33591714.094), stdev = 3333887.972
  CI (99.9%): [25079427.182, 30074122.945] (assumes normal distribution)


# JMH version: 1.21
# VM version: JDK 13.0.2, OpenJDK 64-Bit Server VM, 13.0.2+8
# VM invoker: C:\jdk-13.0.2+8\bin\java.exe
# VM options: <none>
# Warmup: 5 iterations, 10 s each
# Measurement: 5 iterations, 10 s each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: org.apache.commons.lang3.StringUtilCenterTest.test1Old

# Run progress: 75.00% complete, ETA 00:08:24
# Fork: 1 of 5
# Warmup Iteration   1: 42567488.936 ns/op
# Warmup Iteration   2: 55084039.011 ns/op
# Warmup Iteration   3: 40206120.800 ns/op
# Warmup Iteration   4: 57288193.143 ns/op
# Warmup Iteration   5: 40978082.857 ns/op
Iteration   1: 57269681.143 ns/op
Iteration   2: 42055589.076 ns/op
Iteration   3: 51496538.462 ns/op
Iteration   4: 44500411.111 ns/op
Iteration   5: 52760451.579 ns/op

# Run progress: 80.00% complete, ETA 00:06:43
# Fork: 2 of 5
# Warmup Iteration   1: 50089586.000 ns/op
# Warmup Iteration   2: 40182082.731 ns/op
# Warmup Iteration   3: 55439843.094 ns/op
# Warmup Iteration   4: 38485115.769 ns/op
# Warmup Iteration   5: 57708808.621 ns/op
Iteration   1: 43127754.741 ns/op
Iteration   2: 57522725.862 ns/op
Iteration   3: 43491734.632 ns/op
Iteration   4: 53273010.638 ns/op
Iteration   5: 46896654.673 ns/op

# Run progress: 85.00% complete, ETA 00:05:02
# Fork: 3 of 5
# Warmup Iteration   1: 57863772.832 ns/op
# Warmup Iteration   2: 51218231.633 ns/op
# Warmup Iteration   3: 80835640.476 ns/op
# Warmup Iteration   4: 104292427.083 ns/op
# Warmup Iteration   5: 108862696.739 ns/op
Iteration   1: 47689726.190 ns/op
Iteration   2: 99487373.267 ns/op
Iteration   3: 46848762.150 ns/op
Iteration   4: 62012329.630 ns/op
Iteration   5: 59998337.725 ns/op

# Run progress: 90.00% complete, ETA 00:03:22
# Fork: 4 of 5
# Warmup Iteration   1: 64110367.516 ns/op
# Warmup Iteration   2: 51091306.122 ns/op
# Warmup Iteration   3: 48142773.077 ns/op
# Warmup Iteration   4: 48012818.660 ns/op
# Warmup Iteration   5: 48532850.725 ns/op
Iteration   1: 47408419.905 ns/op
Iteration   2: 47231877.358 ns/op
Iteration   3: 54101611.892 ns/op
Iteration   4: 56448726.966 ns/op
Iteration   5: 73093223.358 ns/op

# Run progress: 95.00% complete, ETA 00:01:41
# Fork: 5 of 5
# Warmup Iteration   1: 58022134.682 ns/op
# Warmup Iteration   2: 51917492.746 ns/op
# Warmup Iteration   3: 50538762.626 ns/op
# Warmup Iteration   4: 47698360.476 ns/op
# Warmup Iteration   5: 47873885.646 ns/op
Iteration   1: 46033436.239 ns/op
Iteration   2: 44170253.744 ns/op
Iteration   3: 54631745.109 ns/op
Iteration   4: 45260548.649 ns/op
Iteration   5: 48970378.537 ns/op


Result "org.apache.commons.lang3.StringUtilCenterTest.test1Old":
  53031252.105 ?99.9%) 9048821.218 ns/op [Average]

  (min, avg, max) = (42055589.076, 53031252.105, 99487373.267), stdev = 12079917.438
  CI (99.9%): [43982430.887, 62080073.324] (assumes normal distribution)


# Run complete. Total time: 00:33:42

REMEMBER: The numbers below are just data. To gain reusable insights, you need to follow up on
why the numbers are the way they are. Use profilers (see -prof, -lprof), design factorial
experiments, perform baseline and negative tests that provide experimental control, make sure
the benchmarking environment is safe on JVM/OS/HW level, ask for reviews from the domain experts.
Do not assume the numbers tell you what you want them to tell.

Benchmark                      Mode  Cnt         Score         Error  Units
StringUtilCenterTest.test0New  avgt   25        65.924 ?      2.632  ns/op

StringUtilCenterTest.test0Old  avgt   25        68.175 ?      3.886  ns/op

StringUtilCenterTest.test1New  avgt   25  27576775.064 ?2497347.881  ns/op

StringUtilCenterTest.test1Old  avgt   25  53031252.105 ?9048821.218  ns/op


Benchmark result is saved to target/jmh-result.org.apache.json
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  34:25 min
[INFO] Finished at: 2020-07-08T21:20:48+08:00
[INFO] ------------------------------------------------------------------------

[XenoAmess]

@garydgregory rebased. please find some time to review. thanks.