在.Net 7源码中bool代码优化

public static bool TryParse(ReadOnlySpan<char> value, out bool result)
{
      if (IsTrueStringIgnoreCase(value))  //关注IsTrueStringIgnoreCase
      {
            result = true;
            return true;
      }
      if (IsFalseStringIgnoreCase(value)) //关注和IsFalseStringIgnoreCase
      {
            result = false;
            return true;
      }
      value = TrimWhiteSpaceAndNull(value);
      if (IsTrueStringIgnoreCase(value))
      {
            result = true;
            return true;
      }
      if (IsFalseStringIgnoreCase(value))
      {
            result = false;
            return true;
      }
      result = false;
      return false;
}

//只保留IsTrueStringIgnoreCase和IsFalseStringIgnoreCase
internal static bool IsTrueStringIgnoreCase(ReadOnlySpan<char> value)
{
    // "true" as a ulong, each char |'d with 0x0020 for case-insensitivity
    // 先判断cpu支持大小端模式, 采用无符号long类型存储4个字符的ASCII码值 小端:: 65→e 75→u   72→r  74→t  
    // 将value转为byte数组,读取为ulong类型,然后或运算, 0x20为十六进制 是十进制32  或运算:: A | 32 = a  这样就不用区分大小写
    // 0x0020002000200020为4个0x20,因为值一样,不区分大小端
    ulong true_val = BitConverter.IsLittleEndian ? 0x65007500720074ul : 0x74007200750065ul;
    return value.Length == 4 &&
            (MemoryMarshal.Read<ulong>(MemoryMarshal.AsBytes(value)) | 0x0020002000200020) == true_val;
}

internal static bool IsFalseStringIgnoreCase(ReadOnlySpan<char> value)
{
    // "fals" as a ulong, each char |'d with 0x0020 for case-insensitivity
    // ulong类型只能存4个字符,所以存储 "fals"这4个字符  73→s  6c→l 61→a 66→f 
    // 最后1个字符进行与0x20进行或运算,得到小写字符和'e'进行判断
    ulong fals_val = BitConverter.IsLittleEndian ? 0x73006C00610066ul : 0x660061006C0073ul;
    return value.Length == 5 &&
            (((MemoryMarshal.Read<ulong>(MemoryMarshal.AsBytes(value)) | 0x0020002000200020) == fals_val) &
            ((value[4] | 0x20) == 'e'));
}

public bool TryFormat(Span<char> destination, out int charsWritten)
{
      if (m_value) //为真
      {
            if ((uint)destination.Length > 3u)
            {
                   //进行4次赋值操作
                  destination[0] = 'T';
                  destination[1] = 'r';
                  destination[2] = 'u';
                  destination[3] = 'e';
                  charsWritten = 4;
                  return true;
            }
      }
      else if ((uint)destination.Length > 4u)  //不为真
      {
             //进行5次赋值操作
            destination[0] = 'F';
            destination[1] = 'a';
            destination[2] = 'l';
            destination[3] = 's';
            destination[4] = 'e';
            charsWritten = 5;
            return true;
      }
      charsWritten = 0;
      return false;
}

public bool TryFormat(Span<char> destination, out int charsWritten)
{
    if (m_value)
    {
        if ((uint)destination.Length > 3) // uint cast, per https://github.com/dotnet/runtime/issues/10596
        {
            //先判断cpu支持大小端模式, 采用无符号long类型存储4个字符的ASCII码值 小端:: 65→e 75→u   72→r  74→t  
            //将Span<char>转为byte数组,将true_val写入,减少赋值的次数,与.Net 6中4次赋值操作,这里只有1次
            ulong true_val = BitConverter.IsLittleEndian ? 0x65007500720054ul : 0x54007200750065ul; // "True"
            MemoryMarshal.Write<ulong>(MemoryMarshal.AsBytes(destination), ref true_val);
            charsWritten = 4;
            return true;
        }
    }
    else
    {
        if ((uint)destination.Length > 4)
        {
            //不为真时,进行2次赋值操作 第1次 ulong 只能存4个字符, 第2次通过下标赋值为'e'
            ulong fals_val = BitConverter.IsLittleEndian ? 0x73006C00610046ul : 0x460061006C0073ul; // "Fals"
            MemoryMarshal.Write<ulong>(MemoryMarshal.AsBytes(destination), ref fals_val);
            destination[4] = 'e';
            charsWritten = 5;
            return true;
        }
    }

    charsWritten = 0;
    return false;
}

#define LOWER(c)     (unsigned char)(c | 0x20)