EqualsIgnoreCaseAsciiHelper.cs

using BenchmarkDotNet.Attributes;
using System;

namespace ConsoleApplication2
{
    [Config("jobs=RyuJitX64")]
    public unsafe class CompareOrdinalIgnoreCase
    {
        [Params(1, 5, 12, 50, 100)]
        public int length = 0;

        string test1;
        string test2;

        [Setup]
        public void Setup()
        {
            test1 = new string('A', length);
            test2 = new string('A', length);
        }

        [Benchmark]
        public int CompareOrdinalIgnoreCaseOld()
        {
            return CompareOrdinalIgnoreCaseOld(test1, test2);
        }
        
        [Benchmark]
        public bool EqualsIgnoreCaseAsciiHelper()
        {
            return EqualsIgnoreCaseAsciiHelper(test1, test2);
        }

        public int CompareOrdinalIgnoreCaseOld(String strA, String strB)
        {
            int length = Math.Min(strA.Length, strB.Length);

            fixed (char* ap = strA) fixed (char* bp = strB)
            {
                char* a = ap;
                char* b = bp;

                while (length != 0)
                {
                    int charA = *a;
                    int charB = *b;

                    // uppercase both chars - notice that we need just one compare per char
                    if ((uint)(charA - 'a') <= (uint)('z' - 'a')) charA -= 0x20;
                    if ((uint)(charB - 'a') <= (uint)('z' - 'a')) charB -= 0x20;

                    //Return the (case-insensitive) difference between them.
                    if (charA != charB)
                        return charA - charB;

                    // Next char
                    a++; b++;
                    length--;
                }

                return strA.Length - strB.Length;
            }
        }
        
        public static bool EqualsIgnoreCaseAsciiHelper(String strA, String strB)
        {
            int length = strA.Length;

            fixed (char* ap = strA) fixed (char* bp = strB)
            {
                char* a = ap;
                char* b = bp;

                while (length != 0)
                {
                    int charA = *a;
                    int charB = *b;

                    if (charA == charB ||
                       ((charA | 0x20) == (charB | 0x20) &&
                          (uint)((charA | 0x20) - 'a') <= (uint)('z' - 'a')))
                    {
                        a++;
                        b++;
                        length--;
                    }
                    else
                    {
                        goto ReturnFalse;
                    }
                }

                return true;

                ReturnFalse:
                return false;
            }
        }
    }
}