How to Toggle String Case in .NET

Two more goes and then I'm done. (Wish I could get a job doing this kind of stuff! Wish I could get a job!)

This is similar to my previous attempt but Reflector showed how ToLower() and ToUpper() are implemented and we can save some time by caching the CurrentCulture.TextInfo which saves about 14%:

public static string ToggleCase_SimmoTech(string s)
{
    char[] chs = s.ToCharArray();
    var currentCultureTextInfo = CultureInfo.CurrentCulture.TextInfo;

    for (var i = 0; i < s.Length; ++i)
    {
        char ch = chs[i];

        if (ch <= 0xff)
        {
            if ((ch >= 'A' && ch <= 'Z') || (ch >= 'a' && ch <= 'z') ||
                (ch >= 0xc0 && ch <= 0xde && ch != 0xd7) || (ch >= 0xe0 && ch <= 0xfe && ch != 0xf7))
            {
                chs[i] = (char) (ch ^ 0x20);
            }

            continue;
        }

        switch (char.GetUnicodeCategory(ch))
        {
            case UnicodeCategory.UppercaseLetter:
                chs[i] = currentCultureTextInfo.ToLower(ch);
                break;

            case UnicodeCategory.LowercaseLetter:
                chs[i] = currentCultureTextInfo.ToUpper(ch);
                break;
        }
    }

    return (new string(chs));
}

and finally, my fastest (and last) effort:

To save checking the character ranges which are toggleable, we can use a lookup table like this:

static readonly bool[] ToggleableLatinChars = new[]
 {
      false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false,
      false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false,
      false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false,
      false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false,
      false, true, true, true, true, true, true, true, true, true, true, true, true, true, true, true,
      true, true, true, true, true, true, true, true, true, true, true, false, false, false, false, false,
      false, true, true, true, true, true, true, true, true, true, true, true, true, true, true, true,
      true, true, true, true, true, true, true, true, true, true, true, false, false, false, false, false,
      false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false,
      false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false,
      false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false,
      false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false,
      true, true, true, true, true, true, true, true, true, true, true, true, true, true, true, true,
      true, true, true, true, true, true, true, false, true, true, true, true, true, true, true, false,
      true, true, true, true, true, true, true, true, true, true, true, true, true, true, true, true,
      true, true, true, true, true, true, true, false, true, true, true, true, true, true, true, false
  };

public static string ToggleCase_SimmoTech2(string s)
{
    char[] chs = s.ToCharArray();

    var currentCultureTextInfo = CultureInfo.CurrentCulture.TextInfo;

    for (var i = 0; i < s.Length; ++i)
    {
        char ch = chs[i];

        if (ch <= 0xff)
        {
            if (ToggleableLatinChars[(byte) ch])
            {
                chs[i] = (char) (ch ^ 0x20);
            }

            continue;
        }

        switch (char.GetUnicodeCategory(ch))
        {
            case UnicodeCategory.UppercaseLetter:
                chs[i] = currentCultureTextInfo.ToLower(ch);
                break;

            case UnicodeCategory.LowercaseLetter:
                chs[i] = currentCultureTextInfo.ToUpper(ch);
                break;
        }
    }

    return (new string(chs));
}

This saves 2% or 3% more, but with the extra data required I wouldn't bother unless it was an absolutely speed-critical algorithm.

Cheers,
Simon