runtime: Double doesn't Parse correctly

While doing some mathematical stuff that worked fine in Java I found that C# / .NET does a rather poor job on parsing double values:

Number2Parse=4.3413853813852797e+192 IEEE754=67ee7316b1545878 C#=4.3413853813852797E+192
Number2Parse=4.34138538138528e+192 IEEE754=67ee7316b1545878 C#=4.3413853813852797E+192

You can verify in any browser that 4.3413853813852797e+192 and 4.34138538138528e+192 are distinct values. Version: CLR v4.0.30319

using System;

namespace mathbug
{
    class Program
    {
        static void ShowNumber(string number2Parse)
        {
            double d = Double.Parse(number2Parse);
            ulong ieee754 = (ulong)BitConverter.DoubleToInt64Bits(d);
            Console.WriteLine("Number2Parse=" + number2Parse + " IEEE754=" + Convert.ToString((long)ieee754, 16) + " C#=" + d.ToString("G17"));
        }
 
        static void Main(string[] args)
        {
            ShowNumber("4.3413853813852797e+192");
            ShowNumber("4.34138538138528e+192");
        }
    }
}

About this issue

Original URL
State: closed
Created 6 years ago
Comments: 27 (18 by maintainers)

Most upvoted comments

And it is working as well. SUPER!

cyberphone on Jan 6, 2019

@Suchiman My simple test program didn’t take locale in consideration so ‘.’ doesn’t get interpreted as expected in DE.

Double.Parse(number2Parse) must be changed to use invariant locale. Probably like: Double.Parse(number2Parse, NumberStyles.Float, CultureInfo.InvariantCulture)

cyberphone on Apr 13, 2018

In case you are interested in 100M test values you may download the following file: https://onedrive.live.com/embed?cid=9341770E0D0D5468&resid=9341770E0D0D5468!222&authkey=ADOClRsuPv3_pTk

Associated test program:

using System;
using System.IO;
using System.Globalization;

namespace mathbug
{
    class Program
    {
        static void Main(string[] args)
        {
            using (StreamReader sr = new StreamReader("c:\\es6\\numbers\\es6testfile100m.txt"))
            {
                string line;
                // Read and display lines from the file until the end of 
                // the file is reached.
                long counter = 0;
                while ((line = sr.ReadLine()) != null)
                {
                    string origIeeeHex = line.Substring(0, line.IndexOf(','));
                    while (origIeeeHex.Length < 16)
                    {
                        origIeeeHex = '0' + origIeeeHex;
                    }
                    ulong origIeeeBin = Convert.ToUInt64(origIeeeHex, 16);
                    double origIeee = BitConverter.Int64BitsToDouble((long)origIeeeBin);
                    string number2Parse = line.Substring(line.IndexOf(',') + 1);
                    if (++counter % 100000 == 0)
                    {
                        Console.WriteLine("Count=" + counter);
                    }
                    double parsedIeee = double.Parse(number2Parse, NumberStyles.Float, CultureInfo.InvariantCulture);
                    String parsedIeeeHex = Convert.ToString(BitConverter.DoubleToInt64Bits(parsedIeee), 16);
                    while (parsedIeeeHex.Length < 16)
                    {
                        parsedIeeeHex = '0' + parsedIeeeHex;
                    }
                    bool roundTripOk = parsedIeee.ToString("G17").Equals(origIeee.ToString("G17"));
                    if (origIeee != parsedIeee || !roundTripOk)
                    {
                        Console.WriteLine("Number2Parse={0,-24:S} C#={1,-24:S} Original=" + origIeeeHex + 
                                          " Parsed=" + parsedIeeeHex +
                                          " Roundtrip OK=" +roundTripOk, number2Parse, origIeee.ToString("G17"));
                    }
                }
            }
        }
    }
}

cyberphone on May 3, 2018

I am seeing the direction is to port the parsing code from Roslyn to coreclr

This is one possible direction. I think we should do our homework similar to what we have done for formatting. See what is the state of the art out there, and then pick the best option.

jkotas on Apr 12, 2018