C#中那些[举手之劳]的性能优化

private Point RotatePt(double angle, Point pt)
{
     Point pRet = new Point();
     angle = -angle;
     pRet.X = (int)((double)pt.X * Math.Cos(angle) - (double)pt.Y * Math.Sin(angle));
     pRet.Y = (int)((double)pt.X * Math.Sin(angle) + (double)pt.Y * Math.Cos(angle));
     return pRet;
}

private Point RotatePt3(double angle, Point pt)
{
    Point pRet = new Point();
    angle = -angle;
    double SIN_ANGLE = Math.Sin(angle);
    double COS_ANGLE = Math.Cos(angle);
    pRet.X =(int)(pt.X * COS_ANGLE - pt.Y * SIN_ANGLE);
    pRet.Y = (int)(pt.X * SIN_ANGLE + pt.Y * COS_ANGLE);
    return pRet;
}

public static string ConvertQuot(string html)
{
    Regex regex = new Regex("&(quot|#34);", RegexOptions.IgnoreCase);
    return regex.Replace(html, "\"");
}

readonly static Regex ReplaceQuot = new Regex("&(quot|#34);", RegexOptions.IgnoreCase | RegexOptions.Compiled);
public static string ConvertQuot(string html)
{
    return ReplaceQuot.Replace(html, "\"");
}

public bool Check(int userid)
{
    var user = new User();
    if(GetUser(userid,out user))
    {
        return user.Level > 1;
    }
    return false;
}

public bool Check(int userid)
{
    User user;
    if(GetUser(userid,out user))
    {
        return user.Level > 1;
    }
    return false;
}

//方法1
public static string ConvertQuot1(string html)
{
    return html.Replace(""", "\"").Replace(""", "\"");
}

readonly static Regex ReplaceQuot = new Regex("&(quot|#34);", RegexOptions.IgnoreCase | RegexOptions.Compiled);
//方法2
public static string ConvertQuot2(string html)
{
    return ReplaceQuot.Replace(html, "\"");
}

//方法1
public static string ConvertQuot1(string html)
{
    return html.Replace("0", "").Replace("1", "").Replace("2", "").Replace("3", "").Replace("4", "").Replace("5", "").Replace("6", "").Replace("7", "").Replace("8", "").Replace("9", "");
}

readonly static Regex ReplaceQuot = new Regex("[1234567890]", RegexOptions.IgnoreCase | RegexOptions.Compiled);
//方法2
public static string ConvertQuot2(string html)
{
    return ReplaceQuot.Replace(html, "");
}

readonly static Regex regex = new Regex("[1234567890]", RegexOptions.Compiled);

string s = "";
1) if(s == ""){}
2) if(s == string.Empty){}
3) if (string.IsNullOrEmpty(s)) { }
4) if(s != null && s.Length ==0) {} 
5) if((s+"").Length == 0){}  

public string JoinIds(List<User> users)
{
    StringBuilder sb = new StringBuilder();
    foreach (var user in users)
    {
        sb.Append("'");
        sb.Append(user.Id);
        sb.Append("',");
    }
    sb.Length = sb.Length - 1;
    return sb.ToString();
}

public string JoinIds(List<User> users)
{
    return "'" + string.Join("','", users.Select(it => it.Id)) + "'";
}

public string JoinIds(List<User> users)
{
    var ee = users.GetEnumerator();
    StringBuilder sb = new StringBuilder();
    if (ee.MoveNext())
    {
        sb.Append("'");
        sb.Append(ee.Current.Id);
        sb.Append("'");
        while (ee.MoveNext())
        {
            sb.Append(",'");
            sb.Append(ee.Current.Id);
            sb.Append("'");
        }
    }
    return sb.ToString();
}

//写法1
if(state == 1)
{
    return true;
}
else
{
    return false;
}
//写法2
return state == 1 ? true : false;
//优化后
return state == 1;

Type type = obj.GetType();
switch (type.Name)
{
    case "Int32":
        break;
    case "String":
        break;
    case "Boolean":
        break;
    case "DateTime":
        break;
    ...
    ...
    default:
        break;
}

if (obj is string)
{

}
else if (obj is int)
{

}
else if (obj is DateTime)
{

}
...
...
else
{

}

IConvertible conv = obj as IConvertible;
if (conv != null)
{
    switch (conv.GetTypeCode())
    {
        case TypeCode.Boolean:
            break;
        case TypeCode.Byte:
            break;
        case TypeCode.Char:
            break;
        case TypeCode.DBNull:
            break;
        case TypeCode.DateTime:
            break;
        case TypeCode.Decimal:
            break;
        case TypeCode.Double:
            break;
        case TypeCode.Empty:
            break;
        case TypeCode.Int16:
            break;
        case TypeCode.Int32:
            break;
        ...
        ...
        default:
            break;
    }
}
else
{
    //处理其他类型
}

enum TemplateCode
{
    None = 0,
    Head = 1,
    Menu = 2,
    Foot = 3,
    Welcome = 4,
}

public string GetHtml(TemplateCode tc)
{
    switch (tc)
    {
        case TemplateCode.Head:
            return GetHead();
        case TemplateCode.Menu:
            return GetMenu();
        case TemplateCode.Foot:
            return GetFoot();
        case TemplateCode.Welcome:
            return GetWelcome();
        default:
            throw new ArgumentOutOfRangeException("tc");
    }
}

readonly static Func<string>[] GetTemplate = InitTemplateFunction();

private static Func<string>[] InitTemplateFunction()
{
    var arr = new Func<string>[5];
    arr[1] = GetHead;
    arr[2] = GetMenu;
    arr[3] = GetFoot;
    arr[4] = GetWelcome;
    return arr;
} 

public string GetHtml(TemplateCode tc)
{
    var index = (int)tc;
    if (index >= 1 && index <= 4)
    {
        return GetTemplate[index]();
    }
    throw new ArgumentOutOfRangeException("tc");
}

readonly static Dictionary<TemplateCode, Func<string>> TemplateDict = InitTemplateFunction();

private static Dictionary<TemplateCode, Func<string>> InitTemplateFunction()
{
    var ditc = new Dictionary<TemplateCode, Func<string>>();
    ditc.Add(TemplateCode.Head, GetHead);
    ditc.Add(TemplateCode.Menu, GetMenu);
    ditc.Add(TemplateCode.Foot, GetFoot);
    ditc.Add(TemplateCode.Welcome, GetWelcome);
    return ditc;
} 

public string GetHtml(TemplateCode tc)
{
    Func<string> func;
    if (TemplateDict.TryGetValue(tc,out func))
    {
        return func();
    }
    throw new ArgumentOutOfRangeException("tc");
}

public string Show(char c)
{
    if (c >= '0' && c <= '9')
    {
        return "数字";
    }
    else if (c >= 'a' && c <= 'z')
    {
        return "小写字母";
    }
    else if (c >= 'A' && c <= 'Z')
    {
        return "大写字母";
    }
    else if (c == '/' || c == '\\' || c == '|'
        || c == '$' || c == '#' || c == '+'
        || c == '%' || c == '&' || c == '-'
        || c == '^' || c == '*' || c == '=')
    {
        return "特殊符号";
    }
    else if (c == ',' || c == '.' || c == '!'
        || c == ':' || c == ';' || c == '?'
        || c == '"' || c == '\'')
    {
        return "标点符号";
    }
    else
    {
        return "其他";
    }
}

readonly static byte[] CharMap = InitCharMap();

private static byte[] InitCharMap()
{
    var arr = new byte[char.MaxValue];
    for (char i = '0'; i <= '9'; i++)
    {
        arr[i] = 1;
    }
    for (char i = 'a'; i <= 'z'; i++)
    {
        arr[i] = 2;
    }
    for (char i = 'A'; i <= 'Z'; i++)
    {
        arr[i] = 3;
    }
    arr['/'] = 4;
    arr['\\'] = 4;
    arr['|'] = 4;
    arr['$'] = 4;
    arr['#'] = 4;
    arr['+'] = 4;
    arr['%'] = 4;
    arr['&'] = 4;
    arr['-'] = 4;
    arr['^'] = 4;
    arr['*'] = 4;
    arr['='] = 4;

    arr[','] = 5;
    arr['.'] = 5;
    arr['!'] = 5;
    arr[':'] = 5;
    arr[';'] = 5;
    arr['?'] = 5;
    arr['"'] = 5;
    arr['\''] = 5;
    return arr;
}

public string Show(char c)
{
    switch (CharMap[c])
    {
        case 0:
            return "其他";
        case 1:
            return "数字";
        case 2:
            return "小写字母";
        case 3:
            return "大写字母";
        case 4:
            return "特殊符号";
        case 5:
            return "标点符号";
        default:
            return "其他";
    }
}