Posts in category .net - page 13

Shrinking JS or CSS is premature optimization

Rick Strahl has a post on a JavaScript minifier utility the sole job of which is to shrink the size of your JavaScript whilst making it almost impossible to read in order to save a few kilobytes.I thought I’d take a quick look at what the gain would be and fed it the latest version (1.6) of the very popular Prototype library:

File (KB) GZip (KB)
Standard 121.0 26.7
Shrunk/minified 90.5 22.0
Saving 30.7 4.7

The 30.7 KB saving looks great at first glance but bear in mind that external JavaScript files are cached on the client between page requests and it looses some appeal.If you also consider the fact that most browsers and clients support GZip compression and the savings there are around 4.7 KB and you might wonder if you are wasting your time.In computer science there is a term for blindly attempting to optimize systems without adequate measurement or justification and that term is premature optimization.As Sir Tony Hoare wrote (and Donald Knuth paraphrased)

We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil.

And he was working on computers throughout the 60’s and 70’s that had much less resources than those today.By all means if your server bandwidth is an issue delve into the stats, identify the cause and take it from there. Going with Yahoo’s YSlow plug-in for Firefox/Firebug is a great starting point but remember to analyze the statistics from your own context.

Rick’s tool had shortcomings with non-ASCII characters such as accents, symbols and non-US currency symbols which goes to show how optimization can have other unintended and undesirable effects.

[)amien

Calculating Elf-32 in C# and .NET

GitHub has the latest version of Elf32

Because you can never have enough hashing algorithms at your disposal this one is compatible with the elf_hash function that forms part of the Executable and Linkable Format.

using System;
using System.Security.Cryptography;

public class Elf32 : HashAlgorithm {
  private UInt32 hash;

  public Elf32() {
    Initialize();
  }

  public override void Initialize() {
    hash = 0;
  }

  protected override void HashCore(byte[] buffer, int start, int length) {
    hash = CalculateHash(hash, buffer, start, length);
  }

  protected override byte[] HashFinal() {
    byte[] hashBuffer = UInt32ToBigEndianBytes(hash);
    this.HashValue = hashBuffer;
    return hashBuffer;
  }

  public override int HashSize { get { return 32; } }

  public static UInt32 Compute(UInt32 polynomial, UInt32 seed, byte[] buffer) {
    return CalculateHash(seed, buffer, 0, buffer.Length);
  }

  private static UInt32 CalculateHash(UInt32 seed, byte[] buffer, int start, int size) {
    UInt32 hash = seed;

    for (int i = start; i < size; i++)
       unchecked {
          hash = (hash << 4) + buffer[i];
          UInt32 work = (hash & 0xf0000000);
          if (work != 0)
             hash ^= (work >> 24);
          hash &= ~work;
       }
    return hash;
  }

  private byte[] UInt32ToBigEndianBytes(UInt32 x) {
    return new byte[] {
       (byte)((x >> 24) & 0xff),
       (byte)((x >> 16) & 0xff),
       (byte)((x >> 8) & 0xff),
       (byte)(x & 0xff)
    };
  }
}

[)amien

Publishing .NET applications with prerequisites

Now .NET 3.5 is shipping I took the opportunity to update one of our internal applications and elected to have it install the necessary components (in this case the .NET Framework 3.5) using the Download prerequisites from the same location as my application option.

When trying to install the application via the IIS web server the installer would fail with a download error.

A little testing later I realized the publishing mechanism had placed .msu and .msp files for prerequisites onto the server and of course IIS 6.0 does not serve unknown MIME types.

Both .msu and .msp extensions must be added into the MIME database as application/octet-stream via MMC.

And all was well again.

[)amien

Calculating CRC-64 in C# and .NET

Seeing how the CRC-32 C# class I posted some time ago continues to get lots of Google hits I thought I’d post a CRC-64 version which will no doubt be far less popular being the more limited use. Again, do not use this as a secure message signature, it’s really for backward compatibility with legacy systems.

This is the ISO-3309 version of CRC-64 algorithm. It is not compatible with the ECMA-182 algorithm.

GitHub has the latest version of Crc64

To use this or the CRC-32 class to compute the hash for a file simply:

Crc64 crc64 = new Crc64();
String hash = String.Empty;

using (FileStream fs = File.Open("c:\\myfile.txt", FileMode.Open))
  foreach (byte b in crc64.ComputeHash(fs)) hash += b.ToString("x2").ToLower();

Console.WriteLine("CRC-64 is {0}", hash);

Whilst writing this I considered if I should implement some more advanced hashing algorithms missing from .NET like RIPEMD320 only to stumble across The Legion of Bouncy Castles C# Cryptography APIs which also includes generating PKCS #12 files and a whole bunch of encryption algorithms (but nothing as weak as CRC-64 ;-)

[)amien