Parsing positive integers faster

IntParseBenchmark.cs

using System;
using System.Runtime.CompilerServices;
using BenchmarkDotNet.Attributes;

namespace Jint.Benchmark
{
    [MemoryDiagnoser]
    public class IntParseBenchmark
    {
        private const int N = 1_000_000;
        private static readonly string NString = N.ToString();

        [Benchmark]
        public long ConvertToInt32Substring()
        {
            long sum = 0;
            for (int i = 0; i < N; ++i)
            {
                sum += Convert.ToInt32(NString.Substring(0, NString.Length - 1));
            }

            return sum;
        }

        [Benchmark]
        public long IntParseFast()
        {
            long sum = 0;
            for (int i = 0; i < N; ++i)
            {
                sum += IntParseFast(NString, 0, NString.Length - 1);
            }

            return sum;
        }

        [Benchmark]
        public long IntParseFastUint()
        {
            long sum = 0;
            for (int i = 0; i < N; ++i)
            {
                sum += IntParseFastU(NString, 0, NString.Length - 1);
            }

            return sum;
        }


        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static int IntParseFast(string value, int startIndex, int endIndex)
        {
            int result = 0;
            int length = endIndex;
            for (int i = startIndex; i < length; i++)
            {
                result = 10 * result + (value[i] - 48);
            }

            return result;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static int IntParseFastU(string value, int startIndex, int endIndex)
        {
            int result = 0;
            int length = endIndex;
            for (int i = startIndex; i < (uint) length; i++)
            {
                result = 10 * result + (value[i] - 48);
            }

            return result;
        }
    }
}

BenchmarkDotNet=v0.10.14, OS=Windows 10.0.17134
Intel Core i7-6820HQ CPU 2.70GHz (Skylake), 1 CPU, 8 logical and 4 physical cores
.NET Core SDK=2.1.301
  [Host]     : .NET Core 2.0.7 (CoreCLR 4.6.26328.01, CoreFX 4.6.26403.03), 64bit RyuJIT
  DefaultJob : .NET Core 2.0.7 (CoreCLR 4.6.26328.01, CoreFX 4.6.26403.03), 64bit RyuJIT

Method	Mean	Error	StdDev	Gen 0	Allocated
ConvertToInt32Substring	126.454 ms	0.7954 ms	0.7441 ms	9500.0000	40000000 B
IntParseFast	5.754 ms	0.0390 ms	0.0365 ms	-	0 B
IntParseFastUint	5.028 ms	0.0293 ms	0.0260 ms	-	0 B