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copied!<p>I fooled around with direct char arrays, and your one failing case works with my implementation. The code has been tested well: so do your tests first.</p> <p>You could speed this up by using unsafe code. But I am sure UnicodeEncoding is just as slow (if not slower).</p> <pre><code>/// <summary> /// Represents an encoding that packs bytes tightly into a string. /// </summary> public class ByteEncoding : Encoding { /// <summary> /// Gets the Byte Encoding instance. /// </summary> public static readonly Encoding Encoding = new ByteEncoding(); private ByteEncoding() { } public override int GetBytes(char[] chars, int charIndex, int charCount, byte[] bytes, int byteIndex) { for (int i = 0; i < chars.Length; i++) { // Work out some indicies. int j = i * 2; int k = byteIndex + j; // Get the bytes. byte[] packedBytes = BitConverter.GetBytes((short) chars[charIndex + i]); // Unpack them. bytes[k] = packedBytes[0]; bytes[k + 1] = packedBytes[1]; } return chars.Length * 2; } public override int GetChars(byte[] bytes, int byteIndex, int byteCount, char[] chars, int charIndex) { for (int i = 0; i < byteCount; i += 2) { // Work out some indicies. int j = i / 2; int k = byteIndex + i; // Make sure we don't read too many bytes. byte byteB = 0; if (i + 1 < byteCount) { byteB = bytes[k + 1]; } // Add it to the array. chars[charIndex + j] = (char) BitConverter.ToInt16(new byte[] { bytes[k], byteB }, 0); } return (byteCount / 2) + (byteCount % 2); // Round up. } public override int GetByteCount(char[] chars, int index, int count) { return count * 2; } public override int GetCharCount(byte[] bytes, int index, int count) { return (count / 2) + (count % 2); } public override int GetMaxByteCount(int charCount) { return charCount * 2; } public override int GetMaxCharCount(int byteCount) { return (byteCount / 2) + (byteCount % 2); } } </code></pre> <p>Here is some test code:</p> <pre><code> static void Main(string[] args) { byte[] original = new byte[256]; // Note that we can't tell on the decode side how // long the array was if the original length is // an odd number. This will result in an // inconclusive result. for (int i = 0; i < original.Length; i++) original[i] = (byte) Math.Abs(i - 1); string packed = ByteEncoding.Encoding.GetString(original); byte[] unpacked = ByteEncoding.Encoding.GetBytes(packed); bool pass = true; if (original.Length != unpacked.Length) { Console.WriteLine("Inconclusive: Lengths differ."); pass = false; } int min = Math.Min(original.Length, unpacked.Length); for (int i = 0; i < min; i++) { if (original[i] != unpacked[i]) { Console.WriteLine("Fail: Invalid at a position {0}.", i); pass = false; } } Console.WriteLine(pass ? "All Passed" : "Failure Present"); Console.ReadLine(); } </code></pre> <p>The test works, but you are going to have to test it with your API function.</p>

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