Tuesday, January 15, 2019

Fast String Reversal

Prime Number checking of Fibonacci sequence Number

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
// (c) 2019, Lutfi Shihab


#include <iostream>
#include <vector>
// todo
template <typename T>
class Matrix
{
public:
    Matrix(int rows, int cols) : m_rows(rows), m_cols(cols) {}
    
private:
    int m_rows;
    int m_cols;
};

 
/* function that returns nth Fibonacci number */
template <typename T>
class Fibonacci
{
public:
    Fibonacci(T n) { m_fibNum = fib(n); }
    operator T() const { return m_fibNum; }
    operator int() const { return m_fibNum; }
    
    friend std::ostream& operator<<(std::ostream& os, Fibonacci<T>&  f)
    {
        return os << f.m_fibNum;
    }
    
    Fibonacci<T> operator+=(int k) { return m_fibNum += k; }
    Fibonacci<T> operator %(int k) { return m_fibNum % k; }
    Fibonacci<T> operator /(int k) { return m_fibNum / k; }
    bool         operator<=(int k) { return m_fibNum < k; }
    bool         operator >(int k) { return m_fibNum > k; }
    bool         operator==(int k) { return m_fibNum == k; }

 private:
    void multiply(T F[2][2], T M[2][2])
    {
        T x =  F[0][0]*M[0][0] + F[0][1]*M[1][0]; 
        T y =  F[0][0]*M[0][1] + F[0][1]*M[1][1]; 
        T z =  F[1][0]*M[0][0] + F[1][1]*M[1][0]; 
        T w =  F[1][0]*M[0][1] + F[1][1]*M[1][1]; 
  
        F[0][0] = x; 
        F[0][1] = y; 
        F[1][0] = z; 
        F[1][1] = w;
    }

    /* Optimized version of power() */
    void power(T F[2][2], T n)
    {

        if( n == 0 || n == 1) 
            return; 
        T M[2][2] = {{1,1},{1,0}}; 
  
        this->power(F, n/2); 
        multiply(F, F); 
  
        if (n%2 != 0) 
        multiply(F, M); 
    }

    T fib(T n) 
    { 
        T F[2][2] = {{1,1},{1,0}}; 
        if (n == 0) 
        {
            return 0;
        }
        power(F, n-1); 
  
        return F[0][0]; 
    } 


    T       m_fibNum;
};

  

// Returns n! (the factorial of n)
int Factorial(int n) 
{
    int result = 1;
    for (int i = 1; i <= n; i++) 
    {
        result *= i;
    }

    return result;
}


// Returns true if n is a prime number
template<typename T>
bool IsPrime(T n) 
{
  // Trivial case 1: small numbers
    if (n <= 1) return false;

    // Trivial case 2: even numbers
    if (n % 2 == 0) return n == 2;

    // Now, we have that n is odd and n >= 3.

    // Try to divide n by every odd number i, starting from 3
    for (T i = 3; ; i += 2) 
    {
        // We only have to try i up to the squre root of n
        if (i > n/i) break;

        // Now, we have i <= n/i < n.
        // If n is divisible by i, n is not prime.
        if (n % i == 0) return false;
    }

    // n has no integer factor in the range (1, n), and thus is prime.
    return true;
}



int main()
{
    for(int i=0; i<300; ++i)
    {
        Fibonacci<unsigned long> f(i);
        if (IsPrime(f))
        {
            std::cout << f << " is a prime number\n";
        }
    }
}

Friday, November 30, 2018

Cheap Signal Analyzer



I bought this very cheap 8-input signal analyzer sometime ago on E-Bay, but since then never had time to use it, mostly due to the driver available was for Windows only.  But a few days ago, I plugged it in on my Linux Mint and googled based on VID I found, I stumbled upon a cool opensource project called "SigOk", a complete project to support various embedded instruments, including my signal analyzer.  It comes with a nice GUI front-end called "PulseView".

Operator Overloading in C++

// Assignment operators:
Type &operator&=(Type &lhs, const Type &rhs); // Assign bitwise and
Type &operator^=(Type &lhs, const Type &rhs); // Assign exclusive or
Type &operator|=(Type &lhs, const Type &rhs); // Assign bitwise or
Type &operator-=(Type &lhs, const Type &rhs); // Assign difference
Type &operator<<=(Type &lhs, const Type &rhs); // Assign left shift
Type &operator*=(Type &lhs, const Type &rhs); // Assign product
Type &operator/=(Type &lhs, const Type &rhs); // Assign quotient
Type &operator%=(Type &lhs, const Type &rhs); // Assign remainder
Type &operator>>=(Type &lhs, const Type &rhs); // Assign right shift
Type &operator+=(Type &lhs, const Type &rhs); // Assign sum

//Other modification operators
Type &operator--(Type &lhs); // Prefix decrement - decrement and return new value
Type operator--(Type &lhs, int unused); // Postfix decrement - decrement and return copy of old value
Type &operator++(Type &lhs); // Prefix increment - increment and return new value
Type operator++(Type &lhs, int unused); // Postfix increment - increment and return copy of old value

//Comparison operators
bool operator==(const Type &lhs, const Type &rhs); // Equal
bool operator>(const Type &lhs, const Type &rhs); // Greater than
bool operator>=(const Type &lhs, const Type &rhs); // Greater than or equal
bool operator<(const Type &lhs, const Type &rhs); // less than
bool operator<=(const Type &lhs, const Type &rhs); // less than or equal
bool operator!(const Type &lhs); // logical complement
bool operator!=(const Type &lhs, const Type &rhs); // no equal
//Other operators
Type operator+(const Type &lhs, const Type &rhs); // Addition
Type operator+(const Type &lhs); // Unary plus
Type operator-(const Type &lhs, const Type &rhs); // Subtraction
Type operator-(const Type &lhs); // Unary minus
ContainedType* operator&(const Type &lhs); // Address of
Type operator&(const Type &lhs, const Type &rhs); // Bitwise and
Type operator~(const Type &lhs, const Type &rhs); // Bitwise complement
Type operator^(const Type &lhs, const Type &rhs); // Bitwise exclusive or
Type operator|(const Type &lhs, const Type &rhs); // Bitwise or
Type operator/(const Type &lhs, const Type &rhs); // Division
Type operator<<(const Type &lhs, const Type &rhs); // Left shift
Type operator*(const Type &lhs, const Type &rhs); // Multiplication
ContainedType &operator*(const Type &lhs); // Dereference
Type operator%(const Type &lhs, const Type &rhs); // Remainder
Type operator>>(const Type &lhs, const Type &rhs); // Right shift

class Type
{
 
// Overloads which must be member functions
  ContainedType &operator[](const IndexType &index); // Array subscript
  Type &operator=(const Type &rhs); // Assignment
  ContainedType &operator->*(); // Member reference
  const ContainedType &operator->*() const; // Member reference
  ContainedType &operator->(); // Member reference
  const ContainedType &operator->() const; // Member reference
 
 // Assignment operators
  Type &operator&=(const Type &rhs); // Assign bitwise and
  Type &operator^=(const Type &rhs); // Assign exclusive or
  Type &operator|=(const Type &rhs); // Assign bitwise or
  Type &operator-=(const Type &rhs); // Assign difference
  Type &operator<<=(const Type &rhs); // Assign left shift
  Type &operator*=(const Type &rhs); // Assign product
  Type &operator/=(const Type &rhs); // Assign quotient
  Type &operator%=(const Type &rhs); // Assign remainder
  Type &operator>>=(const Type &rhs); // Assign right shift
  Type &operator+=(const Type &rhs); // Assign sum
//Other modification operators
  Type &operator--(Type &lhs); // Prefix decrement - decrement and return new value
  Type operator--(Type &lhs, int unused); // Postfix decrement - decrement and return copy of old value
  Type &operator++(); // Prefix increment - increment and return new value
  Type operator++(int unused); // Postfix increment - increment and return copy of old value
//Comparison operators
  bool operator==(const Type &rhs) const; // Equal
  bool operator>(const Type &rhs) const; // Greater than
  bool operator>=(const Type &rhs) const; // Greater than or equal 
  bool operator<(const Type &rhs) const; // Less than
  bool operator<=(const Type &rhs) const; // Less than or equal
  bool operator!=(const Type &rhs) const; // Not equal
//Other operators
  Type operator+(const Type &rhs) const; // Addition
  Type operator+() const; // Unary plus
  Type operator-(const Type &rhs) const; // Subtraction
  Type operator-() const; // Unary minus
  ContainedType* operator&(); // Address of
  const ContainedType* operator&() const; // Address of
  Type operator&(const Type &rhs) const; // Bitwise and
  Type operator~(const Type &rhs) const; // Bitwise complement
  Type operator^(const Type &rhs) const; // Bitwise exclusive or
  Type operator|(const Type &rhs) const; // Bitwise or
  ContainedType &operator*(); // Dereference
  const ContainedType &operator*() const; // Dereference
  Type operator/(const Type &rhs) const; // Division
  Type operator<<(const Type &rhs) const; // Left shift
  bool operator!() const; // Logical complement
  Type operator*(const Type &rhs) const; // Multiplication
  Type operator%(const Type &rhs) const; // Remainder
  Type operator>>(const Type &rhs) const; // Right shift
};


Example


Type& Type::operator = (Type const & rhs)
{
    if (&rhs != this)
    {
        // perform assignment to the class T's attributes
    }
    // return by reference
    return *this;
}


Type Type::operator &= (Type const & rhs)
{
    return *this = (*this) & rhs;
}


Type Type::operator & (Type const & rhs)
{
    Type newObjVal;

    // do customized bitwise AND for the type against rhs
    ….

    // return an object by value
    return newObjVal;
}

Type& Type::operator++()  // prefix
{
    ++m_data;
    return *this;
}



class MyClass
{
public:
    // conversion operator, so expression like: Type b = myClass;
    operator Type() { return *m_ptr; }
...
private:
    int m_data;
    Type m_ptr;
};

MyClassMyClass::operator++(int unused)  // postfix
{
    MyClassresult = *this;
    ++m_data;
    // return value before increment
    return result;
}


T* MyClass::operator->() const {return m_ptr; }

// Conversion operator

Tuesday, August 14, 2018

Pointers of String

It is always tricky dealing with string in C/C++, but if we know the rule of evaluation of expression in C++, it's not that hard to understand it.

A string declaration is always evaluated from right to left.  For example, "char *str" is evaluated as "a variable with name 'str' is a pointer (*) of type char".

Another example:

"const char *str" is evaluated as variable str as a pointer of type char that is const (the content is immutable").  (Please remember, "const char .." expression is identical to expression "char const ...")

"char * const str" is evaluated as a variable with name 'str' is a constant pointer to type char, meaning once the pointer is initialized to point to a string, it cannot be changed to point to another string.

"char const * const str" is evaluated as "a variable with name 'str' is a constant pointer to constant char content.  It is a combination to all above.



#include <iostream>

/*

char* str: 
const char* str OR char const *str
char* const str: 
const char* const str: 


*/

#define L(v)       #v << " = " << v

using namespace std;

static char cstr[] = "String ini statis!";

int main()
{
    char*   ps1;  // just a regular pointer to a string
    ps1 = cstr;
    cout << L(ps1) << endl;

#if 0
    char const * p_constr = cstr;
    // the following causes compile error, as it tries to change value of the static string
    *p_constr = '1';
    cout << L(p_constr) << endl;
#endif

    // a dialect of the above (char const *)
    const char* p_constr2 = cstr;
    *p_constr2 = '1';
    cout << L(p_constr2) << endl;


#if 0
    const char* const const_ptr = cstr;  // the pointer cannot be set to different one

    // the following will cause compile error
    const_ptr = cstr2;
    cout << L(const_ptr) << std::endl;
#endif
}