UTF-8文字数取得処理を最適化

[finphie]

fix #161

BenchmarkDotNet v0.13.8, Windows 10 (10.0.19045.3324/22H2/2022Update)
AMD Ryzen 7 5800U with Radeon Graphics, 1 CPU, 16 logical and 8 physical cores
.NET SDK 8.0.100-preview.7.23376.3
  [Host]     : .NET 8.0.0 (8.0.23.37506), X64 RyuJIT AVX2
  Job-ABREFR : .NET 8.0.0 (8.0.23.37506), X64 RyuJIT AVX2

Runtime=.NET 8.0  

Method	Value	Count	Mean	Error	StdDev	Median	Ratio	RatioSD	Allocated	Alloc Ratio
GetLength_Table	a	10	5.946 ns	0.0194 ns	0.0172 ns	5.943 ns	4.08	0.05	-	NA
GetLength_Byte	a	10	3.089 ns	0.0118 ns	0.0111 ns	3.085 ns	2.12	0.03	-	NA
GetLength_PopCount	a	10	1.368 ns	0.0163 ns	0.0153 ns	1.359 ns	0.94	0.01	-	NA
GetLength_PopCount_SoftwareFallback	a	10	2.340 ns	0.0166 ns	0.0156 ns	2.330 ns	1.61	0.01	-	NA
GetLength_Avx2	a	10	1.457 ns	0.0171 ns	0.0160 ns	1.450 ns	1.00	0.00	-	NA
GetLength_Avx2_2	a	10	1.590 ns	0.0239 ns	0.0224 ns	1.580 ns	1.09	0.01	-	NA
GetLength_Table	a	63	101.312 ns	0.0465 ns	0.0412 ns	101.307 ns	13.79	0.06	-	NA
GetLength_Byte	a	63	21.109 ns	0.0497 ns	0.0465 ns	21.104 ns	2.87	0.01	-	NA
GetLength_PopCount	a	63	6.708 ns	0.0355 ns	0.0332 ns	6.726 ns	0.91	0.00	-	NA
GetLength_PopCount_SoftwareFallback	a	63	14.157 ns	0.0217 ns	0.0203 ns	14.153 ns	1.93	0.01	-	NA
GetLength_Avx2	a	63	7.350 ns	0.0339 ns	0.0317 ns	7.364 ns	1.00	0.00	-	NA
GetLength_Avx2_2	a	63	6.643 ns	0.0274 ns	0.0243 ns	6.645 ns	0.90	0.00	-	NA
GetLength_Table	a	64	103.796 ns	0.0536 ns	0.0501 ns	103.791 ns	30.62	0.27	-	NA
GetLength_Byte	a	64	21.688 ns	0.0288 ns	0.0241 ns	21.694 ns	6.39	0.06	-	NA
GetLength_PopCount	a	64	4.969 ns	0.0509 ns	0.0476 ns	4.981 ns	1.47	0.01	-	NA
GetLength_PopCount_SoftwareFallback	a	64	13.232 ns	0.0192 ns	0.0180 ns	13.233 ns	3.90	0.03	-	NA
GetLength_Avx2	a	64	3.390 ns	0.0321 ns	0.0300 ns	3.408 ns	1.00	0.00	-	NA
GetLength_Avx2_2	a	64	2.576 ns	0.0245 ns	0.0229 ns	2.581 ns	0.76	0.01	-	NA
GetLength_Table	a	95	167.258 ns	0.0493 ns	0.0412 ns	167.270 ns	25.88	0.18	-	NA
GetLength_Byte	a	95	32.030 ns	0.0400 ns	0.0375 ns	32.044 ns	4.95	0.03	-	NA
GetLength_PopCount	a	95	9.681 ns	0.0392 ns	0.0367 ns	9.702 ns	1.50	0.01	-	NA
GetLength_PopCount_SoftwareFallback	a	95	21.160 ns	0.0213 ns	0.0200 ns	21.165 ns	3.27	0.02	-	NA
GetLength_Avx2	a	95	6.467 ns	0.0452 ns	0.0423 ns	6.487 ns	1.00	0.00	-	NA
GetLength_Avx2_2	a	95	6.631 ns	0.0443 ns	0.0393 ns	6.637 ns	1.03	0.00	-	NA
GetLength_Table	a	96	169.249 ns	0.1110 ns	0.0984 ns	169.254 ns	47.35	0.37	-	NA
GetLength_Byte	a	96	31.966 ns	0.0707 ns	0.0661 ns	31.965 ns	8.94	0.07	-	NA
GetLength_PopCount	a	96	7.687 ns	0.0420 ns	0.0393 ns	7.672 ns	2.15	0.02	-	NA
GetLength_PopCount_SoftwareFallback	a	96	20.530 ns	0.0817 ns	0.0765 ns	20.554 ns	5.75	0.05	-	NA
GetLength_Avx2	a	96	3.575 ns	0.0350 ns	0.0274 ns	3.572 ns	1.00	0.00	-	NA
GetLength_Avx2_2	a	96	2.845 ns	0.0259 ns	0.0243 ns	2.846 ns	0.80	0.01	-	NA
GetLength_Table	a	1000	2,032.660 ns	0.0483 ns	0.0377 ns	2,032.669 ns	186.89	0.57	-	NA
GetLength_Byte	a	1000	345.936 ns	0.4892 ns	0.4576 ns	346.134 ns	31.82	0.10	-	NA
GetLength_PopCount	a	1000	76.977 ns	0.1456 ns	0.1362 ns	77.002 ns	7.08	0.02	-	NA
GetLength_PopCount_SoftwareFallback	a	1000	215.844 ns	0.3156 ns	0.2952 ns	215.830 ns	19.86	0.07	-	NA
GetLength_Avx2	a	1000	10.869 ns	0.0407 ns	0.0361 ns	10.875 ns	1.00	0.00	-	NA
GetLength_Avx2_2	a	1000	10.000 ns	0.0311 ns	0.0291 ns	9.998 ns	0.92	0.00	-	NA
GetLength_Table	a	10000	20,281.500 ns	0.8826 ns	0.7371 ns	20,281.622 ns	132.82	0.41	-	NA
GetLength_Byte	a	10000	3,416.393 ns	6.2123 ns	5.5070 ns	3,416.605 ns	22.38	0.09	-	NA
GetLength_PopCount	a	10000	720.269 ns	0.7494 ns	0.7010 ns	720.309 ns	4.72	0.01	-	NA
GetLength_PopCount_SoftwareFallback	a	10000	2,136.329 ns	3.1554 ns	2.9516 ns	2,137.231 ns	13.99	0.04	-	NA
GetLength_Avx2	a	10000	152.656 ns	0.4908 ns	0.4591 ns	152.723 ns	1.00	0.00	-	NA
GetLength_Avx2_2	a	10000	83.514 ns	0.2917 ns	0.2728 ns	83.563 ns	0.55	0.00	-	NA
GetLength_Table	a	100000	202,808.383 ns	18.3697 ns	17.1830 ns	202,799.695 ns	129.83	0.43	-	NA
GetLength_Byte	a	100000	34,086.846 ns	67.7887 ns	63.4096 ns	34,117.773 ns	21.82	0.07	-	NA
GetLength_PopCount	a	100000	7,284.385 ns	30.6715 ns	28.6901 ns	7,290.979 ns	4.66	0.02	-	NA
GetLength_PopCount_SoftwareFallback	a	100000	21,355.323 ns	25.7552 ns	22.8313 ns	21,358.696 ns	13.66	0.05	-	NA
GetLength_Avx2	a	100000	1,562.170 ns	5.4931 ns	5.1382 ns	1,561.364 ns	1.00	0.00	-	NA
GetLength_Avx2_2	a	100000	826.393 ns	2.2979 ns	2.1495 ns	826.765 ns	0.53	0.00	-	NA
GetLength_Table	a	10000000	20,287,060.714 ns	1,487.5812 ns	1,318.7020 ns	20,287,040.625 ns	125.80	19.18	12 B	NA
GetLength_Byte	a	10000000	3,087,065.904 ns	20,992.7191 ns	18,609.4987 ns	3,090,924.219 ns	19.15	2.97	2 B	NA
GetLength_PopCount	a	10000000	752,643.157 ns	2,813.9789 ns	2,349.7998 ns	753,526.465 ns	4.62	0.72	-	NA
GetLength_PopCount_SoftwareFallback	a	10000000	2,146,100.167 ns	4,273.0341 ns	3,787.9334 ns	2,145,345.312 ns	13.31	2.03	2 B	NA
GetLength_Avx2	a	10000000	159,107.624 ns	7,073.0639 ns	20,855.0884 ns	152,557.361 ns	1.00	0.00	-	NA
GetLength_Avx2_2	a	10000000	81,713.859 ns	241.2390 ns	225.6551 ns	81,708.478 ns	0.51	0.07	-	NA