C#程序员应该养成的程序性能优化写法

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;
}

//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, "");
}

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){}

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

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
}

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";
    }
}

/// <summary>
/// <para>包含1: 可以为头的字符</para>
/// <para>包含2: 可以为单词的字符</para>
/// <para>包含4: 可以为数字的字符</para>
/// <para>等于8: 空白字符</para>
/// <para>包含16:转义字符</para>
/// <para></para>
/// </summary>
private readonly static byte[] _WordChars = new byte[char.MaxValue];
private readonly static sbyte[] _UnicodeFlags = new sbyte[123];
private readonly static sbyte[, ,] _DateTimeWords;
static UnsafeJsonReader()
{
    for (int i = 0; i < 123; i++)
    {
        _UnicodeFlags[i] = -1;
    }
 
    _WordChars[‘-‘] = 1 | 4;
    _WordChars[‘+‘] = 1 | 4;
 
    _WordChars[‘$‘] = 1 | 2;
    _WordChars[‘_‘] = 1 | 2;
    for (char c = ‘a‘; c <= ‘z‘; c++)
    {
        _WordChars[c] = 1 | 2;
        _UnicodeFlags[c] = (sbyte)(c - ‘a‘ + 10);
    }
    for (char c = ‘A‘; c <= ‘Z‘; c++)
    {
        _WordChars[c] = 1 | 2;
        _UnicodeFlags[c] = (sbyte)(c - ‘A‘ + 10);
    }
 
    _WordChars[‘.‘] = 1 | 2 | 4;
    for (char c = ‘0‘; c <= ‘9‘; c++)
    {
        _WordChars[c] = 4;
        _UnicodeFlags[c] = (sbyte)(c - ‘0‘);
    }
 
    //科学计数法
    _WordChars[‘e‘] |= 4;
    _WordChars[‘E‘] |= 4;
 
    _WordChars[‘ ‘] = 8;
    _WordChars[‘\t‘] = 8;
    _WordChars[‘\r‘] = 8;
    _WordChars[‘\n‘] = 8;
 
    _WordChars[‘t‘] |= 16;
    _WordChars[‘r‘] |= 16;
    _WordChars[‘n‘] |= 16;
    _WordChars[‘f‘] |= 16;
    _WordChars[‘0‘] |= 16;
    _WordChars[‘"‘] |= 16;
    _WordChars[‘\‘‘] |= 16;
    _WordChars[‘\\‘] |= 16;
    _WordChars[‘/‘] |= 16;
 
    string[] a =  { "jan", "feb", "mar", "apr", "may", "jun", "jul", "aug", "sep", "oct", "nov", "dec" };
    string[] b =  { "mon", "tue", "wed", "thu", "fri", "sat", "sun" };
    _DateTimeWords = new sbyte[23, 21, 25];
 
    for (sbyte i = 0; i < a.Length; i++)
    {
        var d = a[i];
        _DateTimeWords[d[0] - 97, d[1] - 97, d[2] - 97] = (sbyte)(i + 1);
    }
 
    for (sbyte i = 0; i < b.Length; i++)
    {
        var d = b[i];
        _DateTimeWords[d[0] - 97, d[1] - 97, d[2] - 97] = (sbyte)-(i + 1);
    }
    _DateTimeWords[‘g‘ - 97, ‘m‘ - 97, ‘t‘ - 97] = sbyte.MaxValue;
}