Features of the mql5 language, subtleties and tricks - page 137

[Nikolai Semko]

Alexey Navoykov:
It does not seem to be about arithmetic operations, because there are none, all values are computed at the compilation stage. The reason is the presence of a loop with an unknown number of iterations (although these iterations average less than two). So your code is somehow optimized by a known number of rand() calls

https://www.mql5.com/ru/forum/308881/page3#comment_11222192

[Nikolai Semko]

Vict:

What do processor developers have to do with it? The generator is software implemented.

No, it's not. This generator is implemented in hardware. This speed cannot be achieved by software - that's obvious.

[[Deleted]]

Nikolai Semko:

No, of course not. This generator is implemented in hardware. This speed cannot be achieved by software - it's obvious.

Actually, the hardware implement a RAND() generator, while rand() is a pseudorandom one.

MathRand

Returns a pseudo-random integer in range 0 to 32767.

I'm not very familiar with hardware, but you'll probably be disappointed - it doesn't seem to work very fast, it's only good as a seed for pseudorandom.

[Nikolai Semko]

Vict:

Well, actually, the hardware implements a RAND() generator, while rand() is a pseudo-random one, it's written in the handbook

I'm not very familiar with the hardware one, but you'll probably be disappointed - it doesn't seem to run very fast, it's only good as seed for pseudorandom.

clearly - pseudo.

Random is much slower(https://en.wikipedia.org/wiki/RdRand)

[[Deleted]]

Nikolai Semko:

Clearly pseudo.

random runs much slower(https://en.wikipedia.org/wiki/RdRand)

Well, yes, pseudo is also shoved in. But I'm sure - rand() is implemented programmatically. Perhaps one of the "older" comrades passing by will confirm it.

[Nikolai Semko]

Vict:

Well, yes, they've put in a pseudo too. But I'm sure - rand() is implemented programmatically. Perhaps one of the "older" comrades passing by will confirm it.

I don't exclude that you may be right. If I have a spare minute, I will try to implement something similar. Although I doubt that I can do it in a nanosecond, but if I can get away from cycles, I think I can do it in 5.

[Nikolai Semko]

Vict:

But I'm sure - rand() is implemented programmatically. Perhaps one of the "older" comrades passing by will confirm it.

Yes, perhaps you're right.
This variant of rand16() function generating pre-random numbers works less than half as slow as the original function and generates random numbers from 0 to 65535.

ushort rand16() { return(((ushort)rand8()<<8)|(ushort)rand8());}


uchar rand8()
{
    staticushort s[10] = { 0x52, 0x8e, 0xdc, 0x61, 0x35, 0xbc, 0x5c, 0xb6 };
    staticushort c = 0xa6;
    staticint i = 0;
    ushort t;
    uchar x;
    
    x = (uchar)s[i];
    t = (ushort)x  + c;
    c = t >> 8;
    c += x;
    x = (uchar)t & 255;
    s[i] = x;
    i++;
    i=i&7;
    return x;
}

i.e. less than 2 nanoseconds.

2019.06.09 23:52:15.855 TestSpeedRand (US30Index,H1)    Время формирования случайных массивов = 9068  микросекунд. Всего сгенерировано 4655770 случайных чисел rand()
2019.06.09 23:52:17.892 TestSpeedRand (US30Index,H1)    Время формирования случайных массивов = 16562 микросекунд. Всего сгенерировано 4655770 случайных чисел rand16()
2019.06.09 23:52:19.940 TestSpeedRand (US30Index,H1)    Время формирования случайных массивов = 22299 микросекунд. Всего сгенерировано 4655770 случайных чисел get_rand()
2019.06.09 23:52:21.986 TestSpeedRand (US30Index,H1)    Время формирования случайных массивов = 20094 микросекунд. Всего сгенерировано 4655770 случайных чисел randUlong()
2019.06.09 23:52:24.020 TestSpeedRand (US30Index,H1)    Время формирования случайных массивов = 14660 микросекунд. Всего сгенерировано 4655770 случайных чисел randUint()
2019.06.09 23:52:26.053 TestSpeedRand (US30Index,H1)    Время формирования случайных массивов = 12543 микросекунд. Всего сгенерировано 4655770 случайных чисел randShort()
2019.06.09 23:52:28.095 TestSpeedRand (US30Index,H1)    Время формирования случайных массивов = 20883 микросекунд. Всего сгенерировано 4655770 случайных чисел RandomLong()

[fxsaber]

// Некоторые возможности структур, которых нет у классов.

// #define struct class // Смотрим ошибки, которые возникают при замене структур на классы.

struct A
{
public:  
  int i;
  
  uint Save( const int handle) { return(FileWriteStruct(handle, this)); } // Запись себя
  uint Load( const int handle) { return(FileReadStruct(handle, this)); }  // Чтение себя
};

// Использование в объединениях
union UNION
{
  uchar b1[sizeof(A)];
  A b2;
};

// Выравнивание
struct pack(sizeof(A)) B : public A
{
  short j;
};

// Структура со скрытым полем
struct C : private A
{
public:  
  void Set( const int Num ) { this.i = Num; }  
  int Get( void ) const { return(this.i); }  
};

// Структура с неизменяемым полем.
struct D
{
public:  
  const A a;
};

template <typename T1, typename T2>
void FromTo( const T1 &ValueFrom, T2 &ValueTo )
{
  uchar Bytes[];    

  StructToCharArray(ValueFrom, Bytes); // В массив байтов
  CharArrayToStruct(ValueTo, Bytes);   // Из массива байтов  
}

void OnStart()
{
  A a[1] = {0};
  
  FileReadArray(0, a);  // Чтение массива
  FileWriteArray(0, a); // Запись массива

  ArrayCopy(a, a); // Копирование массивов
  ZeroMemory(a);   // Обнуление массивов
    
  C c; // Структура со скрытым полем
  c.Set(7);

  FromTo(c, a[0]);
  Print(a[0].i); // Достали значение приватного поля из C.
  
  D d; // Структура с неизменяемым полем.

  a[0].i = 5;
  
  FromTo(a[0], d);
  Print(d.a.i); // Изменили const-поле.    

  FromTo(a[0], c);
  Print(c.Get()); // Изменили private-поле.    
}

In addition, the class object is 16 bytes larger than the object of a similar POD structure. That is, arrays of structures are even more economical.

[Nikolai Semko]

fxsaber:
In addition, the class object is 16 bytes larger than the object of a similar POD structure. Thus, arrays of structures are even more economical.

Class!

[fxsaber]

One of the answers to the question in the quoted thread title

Forum on trading, automated trading systems and testing trading strategies

What is different between Symbol() and _Symbol

fxsaber, 2019.07.07 14:47

void Func( const string& ) {}

void OnStart()
{
  Func(Symbol()); // ERROR: 'Symbol' - parameter passed as reference, variable expected
  Func(_Symbol);  // OK   
}

If Symbol() is called inside a class/structure without ::, it might be more convenient than a predefined variable, as you can make a quick substitution by declaring a method with the same name.