C#根据字节数截取字符串与替换匹配内容的方法

/// <summary>
/// 按最大字节数,截取字符串
/// </summary>
/// <param name="value">要截取的字符串</param>
/// <param name="length">最大长度</param>
/// <returns></returns>
private string Intercept(string value, int length)
{
    if (value.Length * 2 <= length)
    {
      return value;
    }
    string newvalue;
    for (int i = length / 2; i < value.Length; i++)
    {
       newvalue = value.Substring(0, i);
       if (Encoding.Default.GetByteCount(newvalue) > length)
       {
           return value.Substring(0, i - 1);
        }
    }
    return value;
}

private void button1_Click(object sender, EventArgs e)
{
    Regex regx = new Regex(@"[image]", RegexOptions.IgnoreCase);
    string content = textBox1.Text;
  
    Match m = regx.Match(content);
    while (m.Success)
    {
content = content.Remove(m.Index, m.Value.Length);
content = content.Insert(m.Index, "[picture]");
m = regx.Match(content);

    }

    textBox2.Text = content;
}

private void button1_Click(object sender, EventArgs e)
{
    Regex regx = new Regex(@"[image]", RegexOptions.IgnoreCase);
    string content = textBox1.Text;
    content=regx.Replace(content, new MatchEvaluator(DoMatch));
    textBox2.Text = content;
}

private string DoMatch(Match m)
{
    return "[picture]";
}

function fmt(s) {
    var value = s.replace(/,/g, "");
    var v = value.replace(/(d+)(.d+)?/, "$1");
    var d = value.replace(/(d+)(.d+)?/, "$2");
    var reg = /d{4,}b/;
    while (reg.test(v)) {
v = v.replace(/(d{3})b/, ',$1');
    }
    return v + d; ;
}