net5

[bitfaster]

Migrate to public span based convert API, all unit tests pass on net5 target.

dotnet run -f net5.0 -c Release --job short --runtimes netcoreapp50 --filter *StringFromBase64Loh*

BenchmarkDotNet=v0.12.1, OS=Windows 10.0.22000
Intel Core i7-1065G7 CPU 1.30GHz, 1 CPU, 8 logical and 4 physical cores
.NET Core SDK=5.0.405
  [Host]     : .NET Core 5.0.14 (CoreCLR 5.0.1422.5710, CoreFX 5.0.1422.5710), X64 RyuJIT
  Job-WLZFHQ : .NET Core 5.0.14 (CoreCLR 5.0.1422.5710, CoreFX 5.0.1422.5710), X64 RyuJIT

Runtime=.NET Core 5.0  Toolchain=netcoreapp50  IterationCount=3
LaunchCount=1  WarmupCount=3

Method	Mean	Error	StdDev	Ratio	Gen 0	Gen 1	Gen 2	Allocated
ConvertFrom	1,159.8 us	209.3 us	11.47 us	1.00	324.2188	324.2188	324.2188	1464.88 KB
StreamFrom	1,141.5 us	449.9 us	24.66 us	0.98	195.3125	195.3125	195.3125	978.05 KB
GetBytes	181.4 us	238.4 us	13.07 us	0.16	137.9395	137.9395	137.9395	651.07 KB

dotnet run -f net5.0 -c Release --job short --runtimes netcoreapp50 --filter *StreamFromBase64*

Runtime=.NET Core 5.0  Toolchain=netcoreapp50  IterationCount=3
LaunchCount=1  WarmupCount=3

Method	input	Mean	Error	StdDev	Ratio	RatioSD	Gen 0	Gen 1	Gen 2	Allocated
ConvertFrom	1024	1,885.4 ns	394.39 ns	21.62 ns	1.00	0.00	0.7439	-	-	3120 B
StreamFrom	1024	1,874.2 ns	607.79 ns	33.31 ns	0.99	0.03	0.0401	-	-	168 B
ConvertFrom	131072	335,511.0 ns	168,510.10 ns	9,236.61 ns	1.00	0.00	124.5117	124.5117	124.5117	393264 B
StreamFrom	131072	217,118.6 ns	100,933.58 ns	5,532.51 ns	0.65	0.00	-	-	-	168 B
ConvertFrom	16384	27,378.6 ns	6,776.70 ns	371.45 ns	1.00	0.00	11.6882	-	-	49200 B
StreamFrom	16384	27,171.7 ns	7,806.86 ns	427.92 ns	0.99	0.02	0.0305	-	-	168 B
ConvertFrom	2048	3,627.9 ns	1,052.74 ns	57.70 ns	1.00	0.00	1.4763	-	-	6192 B
StreamFrom	2048	3,564.2 ns	1,143.63 ns	62.69 ns	0.98	0.03	0.0381	-	-	168 B
ConvertFrom	256	537.5 ns	106.19 ns	5.82 ns	1.00	0.00	0.1945	-	-	816 B
StreamFrom	256	628.8 ns	69.48 ns	3.81 ns	1.17	0.01	0.0401	-	-	168 B
ConvertFrom	32768	55,648.4 ns	24,753.53 ns	1,356.82 ns	1.00	0.00	23.2544	-	-	98352 B
StreamFrom	32768	56,219.0 ns	4,409.07 ns	241.68 ns	1.01	0.03	-	-	-	168 B
ConvertFrom	4096	7,147.8 ns	1,930.95 ns	105.84 ns	1.00	0.00	2.9449	-	-	12336 B
StreamFrom	4096	7,091.8 ns	1,949.01 ns	106.83 ns	0.99	0.03	0.0381	-	-	168 B
ConvertFrom	512	1,001.8 ns	90.77 ns	4.98 ns	1.00	0.00	0.3777	-	-	1584 B
StreamFrom	512	1,122.2 ns	228.36 ns	12.52 ns	1.12	0.02	0.0401	-	-	168 B
ConvertFrom	65536	159,749.9 ns	70,582.66 ns	3,868.87 ns	1.00	0.00	41.5039	41.5039	41.5039	196656 B
StreamFrom	65536	108,982.0 ns	116,953.01 ns	6,410.59 ns	0.68	0.05	-	-	-	168 B
ConvertFrom	8192	13,944.8 ns	3,303.35 ns	181.07 ns	1.00	0.00	5.8594	-	-	24624 B
StreamFrom	8192	13,575.3 ns	4,283.37 ns	234.79 ns	0.97	0.02	0.0305	-	-	168 B

[bitfaster]

How about using this:
https://docs.microsoft.com/en-us/dotnet/api/system.buffers.text.base64?view=net-5.0