Decimal 割りまくる

Benchmark-report-github.md

BenchmarkDotNet=v0.10.14, OS=Windows 10.0.17692
Intel Core i7-3770 CPU 3.40GHz (Ivy Bridge), 1 CPU, 8 logical and 4 physical cores
  [Host]     : .NET Framework 4.7.1 (CLR 4.0.30319.42000), 32bit LegacyJIT-v4.7.3062.0
  DefaultJob : .NET Framework 4.7.1 (CLR 4.0.30319.42000), 32bit LegacyJIT-v4.7.3062.0

Method	Source	Mean	Error	StdDev
UseToString	123.456	438.9 ns	7.701 ns	7.204 ns
UseDecimal	123.456	1,252.4 ns	11.789 ns	9.845 ns

CountSyosu.cs

using System;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;

namespace ConsoleApp9
{
    class Program
    {
        static void Main(string[] args)
        {
            BenchmarkRunner.Run<Benchmark>();
        }
    }

    public class Benchmark
    {
        [Params(123.456)]
        public double Source;

        [Benchmark]
        public (int seisu, int syosu) UseToString()
        {
            var xStr = this.Source.ToString("F99", System.Globalization.CultureInfo.InvariantCulture);
            var dotIndex = xStr.IndexOf('.');

            var syosuCount = 0;
            for (var i = dotIndex + 1; i < xStr.Length; i++)
            {
                if (xStr[i] != '0') syosuCount = i - dotIndex;
            }

            return (dotIndex, syosuCount);
        }

        [Benchmark]
        public (int seisu, int syosu) UseDecimal()
        {
            var x = (decimal)this.Source;

            // 整数部
            var seisuCount = 0;
            var tmp1 = x;
            while (tmp1 >= 1m)
            {
                tmp1 /= 10m;
                seisuCount++;
            }

            // 小数部
            var syosuCount = 0;
            var tmp2 = Math.Abs(x) % 1.0m;
            while (tmp2 > 0m)
            {
                tmp2 = tmp2 * 10m % 1.0m;
                syosuCount++;
            }

            return (seisuCount, syosuCount);
        }
    }
}