SplitOnWhiteSpace is 400 times faster than String.Split for large text.

SplitOnWhiteSpace.cs

        /// <summary>
        /// Split string on whitespace
        /// </summary>
        /// <remarks>
        /// Faster than String.Split for large strings.
        /// Results from splitting 1000 email text files
        /// text.Split(new char[] {}, StringSplitOptions.RemoveEmptyEntries)
        /// 00:00:00.0008075 2134951 Tokens StringHelper.SplitOnWhiteSpace
        /// 00:00:00.3263374 2134951 Tokens String.Split
        /// </remarks>
        /// <param name="text"></param>
        /// <returns></returns>
        public static IEnumerable<string> SplitOnWhiteSpace(string text)
        {
            var startIndex = 0;
            for (var i = 0; i < text.Length; i++)
            {
                if (!char.IsWhiteSpace(text[i]))
                {
                    continue;
                }
                if (startIndex != i)
                {
                    yield return text.Substring(startIndex, i - startIndex);
                }
                startIndex = i + 1;
            }
            if (startIndex < text.Length)
            {
                yield return text.Substring(startIndex, text.Length - startIndex);
            }
        }