blambert/codesnip – Fast byte array to hex string conversion.

Article
02/22/2009

Got a tight loop where you convert an array of bytes into a hex string? Here’s a blambert/codesnip:

 /// <summary>
/// Hex string lookup table.
/// </summary>
private static readonly string[] HexStringTable = new string[]
{
    "00", "01", "02", "03", "04", "05", "06", "07", "08", "09", "0A", "0B", "0C", "0D", "0E", "0F",
    "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "1A", "1B", "1C", "1D", "1E", "1F",
    "20", "21", "22", "23", "24", "25", "26", "27", "28", "29", "2A", "2B", "2C", "2D", "2E", "2F",
    "30", "31", "32", "33", "34", "35", "36", "37", "38", "39", "3A", "3B", "3C", "3D", "3E", "3F",
    "40", "41", "42", "43", "44", "45", "46", "47", "48", "49", "4A", "4B", "4C", "4D", "4E", "4F",
    "50", "51", "52", "53", "54", "55", "56", "57", "58", "59", "5A", "5B", "5C", "5D", "5E", "5F",
    "60", "61", "62", "63", "64", "65", "66", "67", "68", "69", "6A", "6B", "6C", "6D", "6E", "6F",
    "70", "71", "72", "73", "74", "75", "76", "77", "78", "79", "7A", "7B", "7C", "7D", "7E", "7F",
    "80", "81", "82", "83", "84", "85", "86", "87", "88", "89", "8A", "8B", "8C", "8D", "8E", "8F",
    "90", "91", "92", "93", "94", "95", "96", "97", "98", "99", "9A", "9B", "9C", "9D", "9E", "9F",
    "A0", "A1", "A2", "A3", "A4", "A5", "A6", "A7", "A8", "A9", "AA", "AB", "AC", "AD", "AE", "AF",
    "B0", "B1", "B2", "B3", "B4", "B5", "B6", "B7", "B8", "B9", "BA", "BB", "BC", "BD", "BE", "BF",
    "C0", "C1", "C2", "C3", "C4", "C5", "C6", "C7", "C8", "C9", "CA", "CB", "CC", "CD", "CE", "CF",
    "D0", "D1", "D2", "D3", "D4", "D5", "D6", "D7", "D8", "D9", "DA", "DB", "DC", "DD", "DE", "DF",
    "E0", "E1", "E2", "E3", "E4", "E5", "E6", "E7", "E8", "E9", "EA", "EB", "EC", "ED", "EE", "EF",
    "F0", "F1", "F2", "F3", "F4", "F5", "F6", "F7", "F8", "F9", "FA", "FB", "FC", "FD", "FE", "FF"
};

/// <summary>
/// Returns a hex string representation of an array of bytes.
/// </summary>
/// <param name="value">The array of bytes.</param>
/// <returns>A hex string representation of the array of bytes.</returns>
public static string ToHex(this byte[] value)
{
    StringBuilder stringBuilder = new StringBuilder();
    if (value != null)
    {
        foreach (byte b in value)
        {
            stringBuilder.Append(HexStringTable[b]);
        }
    }

    return stringBuilder.ToString();
}

The above approach runs 25% faster than using a small hex alphabet and doing something like:

 StringBuilder stringBuilder = new StringBuilder();
string hexAlphabet = "0123456789ABCDEF";
if (value != null)
{
    foreach (byte b in value)
    {
        stringBuilder.Append(hexAlphabet[(int)(b >> 4)]);
        stringBuilder.Append(hexAlphabet[(int)(b & 0xF)]);
    }
}

And so much faster than doing:

 stringBuilder.Append(b.ToString("X2"));

in the foreach loop, it’s not even funny.

(In a large test run, averaged over 40 passes, the b.ToString("X2") approach took ~900ms and the ToHex method above took ~198ms).

Brian

blambert/codesnip – Fast byte array to hex string conversion.

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