A SoundEx implementation in .NET

using System;
using System.Text;

namespace ThunderMain.SoundEx {
	
	/// <summary>
	/// Implements American SoundEx or Miracode algorithm according 
	/// to http://www.nara.gov/genealogy/soundex/soundex.html
	/// Miracode was first used with the 1910 US census
	/// </summary>
	internal class MiracodeSoundEx : ISoundEx{

		public override string GenerateSoundEx(string s) {
			StringBuilder output=new StringBuilder();

			if(s.Length>0) {

				output.Append(Char.ToUpper(s[0]));

				// Stop at a maximum of 4 characters
				for(int i=1; i<s.Length && output.Length<4; i++) {

					string c=EncodeChar(s[i]);

					// We either append or ignore, determined by the preceding char
					switch(Char.ToLower(s[i-1])) {
						case 'h':
						case 'w':
							// Don't encode the consonant
							break;
						case 'a':
						case 'e':
						case 'i':
						case 'o':
						case 'u':
							// Chars separated by a vowel - OK to encode
							output.Append(c);					

							break;
						default:
							// Ignore duplicated phonetic sounds
							if(output.Length==1) {
								// We only have the first character, which is never
								// encoded. However, we need to check whether it is
								// the same phonetically as the next char
								if(EncodeChar(output[output.Length-1])!=c)
									output.Append(c);
							} else {
								if(output[output.Length-1].ToString()!=c)
									output.Append(c);
							}
							
							break;
					}
				}

				// Pad with zeros
				for(int i=output.Length; i<4; i++) {
					output.Append("0");
				}
			}
	
			return output.ToString();
		}
		private void AssertEquals(string s1, string s2, string error) {
			if(!s1.Equals(s2))
				throw new Exception(error + ". Expected " + s2 + " but got " + s1);
		}
		public override void ValidateAlgorithm() {
			// Validate the SoundEx agorithm
			// using http://www.nara.gov/genealogy/soundex/soundex.html

			AssertEquals(GenerateSoundEx("Tymczak"),"T522", "SoundEx Algoritm Broken");
			AssertEquals(GenerateSoundEx("Ashcraft"),"A261", "SoundEx Algoritm Broken");
			AssertEquals(GenerateSoundEx("Pfister"),"P236", "SoundEx Algoritm Broken");
			AssertEquals(GenerateSoundEx("Jackson"),"J250", "SoundEx Algoritm Broken");
			AssertEquals(GenerateSoundEx("Gutierrez"),"G362", "SoundEx Algoritm Broken");
			AssertEquals(GenerateSoundEx("VanDeusen"),"V532", "SoundEx Algoritm Broken");
			AssertEquals(GenerateSoundEx("Deusen"),"D250", "SoundEx Algoritm Broken");
		}


	}
}