Palindrome

Performance test of several methods to check the input string for palindrome.

A palindrome is a word, number, phrase, or other sequence of characters which reads the same backward as forward, such as madam or racecar.

1. ReverseTest method uses string.Reverse()
2. LoopTest method uses loop for a index
3. SpanTest method uses unsafe context, readonly span and pointers in while loop

A simple loop seems to be the best solution in terms of performance:

public bool IsPalindromeLoop(string input)
{
    if (string.IsNullOrWhiteSpace(input))
    {
        return true;
    }

    var j = input.Length - 1;

    for (var i = 0; i < input.Length / 2; i++)
    {
        var left = input[i];
        var right = input[j - i];
        if (char.ToLowerInvariant(left) != char.ToLowerInvariant(right))
        {
            return false;
        }
    }

    return true;
}

BenchmarkDotNet=v0.13.1, OS=Windows 10.0.22000
Intel Core i7-9700 CPU 3.00GHz, 1 CPU, 8 logical and 8 physical cores
.NET SDK=6.0.303
  [Host]     : .NET 6.0.8 (6.0.822.36306), X64 RyuJIT
  DefaultJob : .NET 6.0.8 (6.0.822.36306), X64 RyuJIT

Method	Input	Mean	Error	StdDev	Median	Completed Work Items	Lock Contentions	Gen 0	Allocated
ReverseTest	****	2.007 ns	0.0160 ns	0.0149 ns	2.006 ns	-	-	-	-
LoopTest		2.231 ns	0.0208 ns	0.0194 ns	2.228 ns	-	-	-	-
SpanTest		2.182 ns	0.0653 ns	0.0802 ns	2.173 ns	-	-	-	-
ReverseTest	#1AzZa1#	240.768 ns	3.1385 ns	3.9692 ns	241.112 ns	-	-	0.0305	192 B
LoopTest	#1AzZa1#	18.957 ns	0.2280 ns	0.2021 ns	18.936 ns	-	-	-	-
SpanTest	#1AzZa1#	21.154 ns	0.1880 ns	0.1468 ns	21.156 ns	-	-	-	-
ReverseTest	1+ěšč(...)ČŠĚ+1 [22]	478.518 ns	8.9228 ns	16.0897 ns	470.760 ns	-	-	0.0706	448 B
LoopTest	1+ěšč(...)ČŠĚ+1 [22]	326.415 ns	5.3685 ns	4.4830 ns	327.455 ns	-	-	-	-
SpanTest	1+ěšč(...)ČŠĚ+1 [22]	328.454 ns	1.8821 ns	1.6685 ns	328.244 ns	-	-	-	-
ReverseTest	Aba	161.541 ns	1.5774 ns	1.4755 ns	161.722 ns	-	-	0.0279	176 B
LoopTest	Aba	7.285 ns	0.0304 ns	0.0238 ns	7.283 ns	-	-	-	-
SpanTest	Aba	7.902 ns	0.1121 ns	0.1048 ns	7.853 ns	-	-	-	-
ReverseTest	a	114.406 ns	0.8297 ns	0.7761 ns	114.578 ns	-	-	0.0267	168 B
LoopTest	a	3.429 ns	0.0276 ns	0.0258 ns	3.419 ns	-	-	-	-
SpanTest	a	3.889 ns	0.0681 ns	0.0637 ns	3.889 ns	-	-	-	-
ReverseTest	ab	129.687 ns	1.7197 ns	1.5245 ns	129.663 ns	-	-	0.0279	176 B
LoopTest	ab	6.754 ns	0.0978 ns	0.0816 ns	6.730 ns	-	-	-	-
SpanTest	ab	6.877 ns	0.0468 ns	0.0415 ns	6.875 ns	-	-	-	-
ReverseTest	aba	128.894 ns	1.5863 ns	1.4839 ns	128.895 ns	-	-	0.0279	176 B
LoopTest	aba	6.529 ns	0.0649 ns	0.0542 ns	6.515 ns	-	-	-	-
SpanTest	aba	6.812 ns	0.0727 ns	0.0680 ns	6.772 ns	-	-	-	-