C#: Fast string comparison optimization

re: C#: Fast string comparison optimization

Ayende Rahien — Sat, 07 Jan 2006 00:39:45 GMT

Honestly, why do you _care_ for this?
I run a _billion_ string comparision in 1.5 seconds.

This performance difference is so small that I don't even think about it until I start doing profiling, and _that_ optimization is _way_ down the list.

re: C#: Fast string comparison optimization

Frank — Sat, 07 Jan 2006 03:30:14 GMT

what about the switch statement? or has that just the same performance as the else if?
Ayende has a point, but well, its always nice to know :-)

re: C#: Fast string comparison optimization

abhinaba — Sat, 07 Jan 2006 10:03:54 GMT

Frank take a look into http://blogs.msdn.com/abhinaba/archive/2005/10/28/486173.aspx. In this blog I had posted about common string comparisons and how they work including switch. in Switch the overloded == operator is called so the final comparison occurs in String.Equal(string, string)

As you said its nice to know. In case your application does lot of string comparison the info might be helpful... Anyways for framework development its always nice to know where time is being taken in your API... But as usual optimize only based on profiling and only when the data shows you are not meeting your perf criteria. For all other purpose elegance and maintainability wins over optimization

re: C#: Fast string comparison optimization

kfarmer — Sat, 07 Jan 2006 12:33:04 GMT

Does the framework's shortcut still require the strings be interned, then?

re: C#: Fast string comparison optimization

abhinaba — Sat, 07 Jan 2006 13:46:01 GMT

The reference match succeeds only for interned string. The point is I had said in the earlier post that to take the benefit of interned string explicitly do a Object reference match. With the new info I got you are equaly good if you do a string.Equals(a,b) kind of comparison. However, both strings have to be interned....

re: C#: Fast string comparison optimization

Magnus Hiie — Sat, 07 Jan 2006 18:23:44 GMT

I think the ReferenceEquals method is still faster if the strings are interned because when the strings are _not_ equal, the == operator and string.Equals still perform string comparision, however ReferenceEquals can just return false.

re: C#: Fast string comparison optimization

TAG — Sat, 07 Jan 2006 20:12:47 GMT

BTW, Why interning requere you to change reference value in your code ?
Why Runtime unable to change reference for you automaticaly ? It's allowed to move pointers all over heap as long as they are not pined.

I.e. my suggestion is to make string.Intern() returning void.
This can be smart move - once string.Equals operator (or ==) find two exact strings but at different locations - then reference to one of them will be changed to another; second unreferenced and become eligible for garbage collection (even more - all others references to second string will be noticed during GC and changed).

String.Equals Performance Comparison

Noah Coad — Fri, 29 Jun 2007 18:54:31 GMT

I recently had an app that I used the VSTS Profiler on to find that a significant portion of time was

re: C#: Fast string comparison optimization

Elz — Wed, 30 Jan 2008 00:35:31 GMT

Well, i made some tests for 2 strings:

string a = "ASDFGHJKL";

string b = "ASDFGHJ";

In my measurements a.Equals(b)(average: 864 ms) performed a lot faster than string.Equals(a,b) (average: 2395).

I used Framework 2.0.

So if you could enlighten me i would appreciate.

re: C#: Fast string comparison optimization

abhinaba — Wed, 30 Jan 2008 06:42:07 GMT

Do the same in a loop for say 100,000 times and then take the average....

re: C#: Fast string comparison optimization

Elz — Thu, 31 Jan 2008 00:02:56 GMT

Hi!

Here is my code:

using System;

using System.Diagnostics;

namespace ConsoleApplication3

{

class Program

{

static void Main(string[] args)

{

string a = "ASDFGHJKL";

string b = "ASDFGHJ";

Stopwatch stopper = new Stopwatch();

stopper.Start();

for (long i = 0; i < 200000000; i++)

{

//string.Equals(a, b);

a.Equals(b);

}

stopper.Stop();

Console.WriteLine("Time: {0}", stopper.ElapsedMilliseconds);

}

a.Equals(b) - takes around 1650 ms.

string.Equals(a,b) - takes around 4900 ms.

So what is the catch?

re: C#: Fast string comparison optimization

shareef — Thu, 10 Apr 2008 21:15:28 GMT

Elz is correct on my Dual Xeon procesor,

a.Equals(b) - 1409 ms

string.Equals(a,b) - 1610 ms

a == b - 1610 ms

re: C#: Fast string comparison optimization

shareef — Thu, 10 Apr 2008 21:18:14 GMT

Also, c# reference says string == operator checks for values not reference.

http://msdn2.microsoft.com/en-us/library/53k8ybth.aspx

re: C#: Fast string comparison optimization

itsmarik — Thu, 08 May 2008 20:16:55 GMT

Here is what I found...

If a=b, string.Equals(a, b) is fastest. If a <> b or a.Length <> b.Length, a.Equals(b) is fastest.

The example Elz gave, a and b have different lengths.

Probably something missed

tomas — Mon, 30 Jun 2008 01:55:24 GMT

When looking on this results think that it is not better to use static Equals() - is fastest only if strings are same - or is good only if we just testing and expecting that string equals, but always - it plays role only in case of huge usage of string comparisons.

This are meassures from testing code:

* m1 = first method a.Equals(b)

* m2 = second method string.Equals(a, b)

(using == operator is almost same then m2, but always very little slower)

CNT = 20.000.000

1. different length : m1=199 m2=216

2. same length but different: m1=473 m2=499

3. same strings : m1=485 m2=118

CNT = 2.000.000.000

1. different length : m1=18708 m2=21120

2. same length but different: m1=47607 m2=49944

3. same strings : m1=48626 m2=11262

Stringing along in .NET… « akutz’s blog

Stringing along in .NET… « akutz’s blog — Sun, 20 Jul 2008 19:57:22 GMT

PingBack from http://akutz.wordpress.com/2008/07/20/stringing-along-in-net/

re: C#: Fast string comparison optimization

Schley Andrew Kutz — Mon, 21 Jul 2008 03:22:14 GMT

I did some research on the topic at http://akutz.wordpress.com/2008/07/20/stringing-along-in-net/

re: C#: Fast string comparison optimization

Schley Andrew Kutz — Mon, 21 Jul 2008 03:22:16 GMT

I did some research on the topic at http://akutz.wordpress.com/2008/07/20/stringing-along-in-net/

re: C#: Fast string comparison optimization

MrY — Tue, 29 Jul 2008 15:42:03 GMT

I think the string comparison optimizatioin is not so useful.

I wound rather to use the "a.Equals(b)".

I think the optimization of string contains() or indexof() is more useful.

re: C#: Fast string comparison optimization

Jan — Tue, 21 Oct 2008 20:51:21 GMT

The reason is, that both String.Equals(Object) and String.Equals(String) are virtual, thus cannot be inlined, whilst static String.Equals(String,String) can.