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Optimize C and C++ Code

Optimize C and C++ codeWith the advent of mobile devices, optimizing code has become even more important. Faster applications not only improve the user experience, they also improve battery life.

Optimizing C++ and C Code discusses several techniques that will help improve the performance.

  1. Premature optimization is the root of all evil
  2. Adjust structure sizes to power of two
  3. Place case labels in narrow range
  4. Place frequent case labels first
  5. Break big switch statements into nested switches
  6. Minimize local variables
  7. Declare local variables in the inner most scope
  8. Reduce the number of parameters
  9. Use references for parameter passing and return value for types bigger than 4 bytes
  10. Don’t define a return value if not used
  11. Consider locality of reference for code and data
  12. Locality of reference in multi-dimensional arrays
  13. Prefer int over char and short
  14. Define lightweight constructors
  15. Prefer initialization over assignment
  16. Use constructor initialization lists
  17. Do not declare “just in case” virtual functions
  18. In-line 1 to 3 line functions
  19. Avoid cascaded function calls
  20. Prefer preincrement over postincrement
  21. Define move constructors in C++11
  22. Use hardware accelerators and SIMD hardware
  23. Use profile guided optimization


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C++ Internals: Mapping from C++ classes and methods to C structs and functions

Mapping from C++ to C code

C++ internals can be better understood by mapping them to corresponding C code.

Refer to the article mapping from C++ classes and methods to C structs and functions.

The contents of the article are summarized below.

This pointer maps to an additional parameter

A C++ method maps to a C method with an additional this pointer. For example, the UpdateX method C++ method…

void A::UpdateX(int newX)
{
  if (g_y != 0 && m_x < newX)
  {
    m_x = newX;
  }
}

…translates to the following C code:

void A_UpdateX(A *this_ptr, int newX)
{
  if (g_y != 0 && this_ptr->m_x < newX)
  {
     this_ptr->m_x = newX;
  }
}

Complete article: Mapping from C++ classes and methods to C structs and functions.

A class maps to a struct with associated methods

A C++ class is equivalent to a C structure with a class methods. The following class…

class A
{
private:
  int m_x;
  static int g_y;
  int m_z;

  // Should be invoked when the object ends
  void InformEnd();

public:
  A(int x);
  ~A();
  void UpdateX(int newX);
  static void UpdateY(int newY);
};

…is represented as the C structure with functions.

  • Methods have a corresponding this pointer.
  • Static methods are functions that do not get an additional this pointer.
  • Static variables map to global variables.
struct A
{
  int m_x;
  int m_z;
};
int g_y = 0; /* Represents static variable */
A *A_Constructor(A *this_ptr, int x);
void A_Destructor(A *this_ptr, BOOLEAN dynamic);
void A_UpdateX(A *this_ptr, int newX);
void A_UpdateY(int newY); /* Represents a static method. */

Complete article: Mapping from C++ classes and methods to C structs and functions.

Constructor representation in C

In C++, objects may be allocated on the heap or the stack. This has implications in the mapping from a C++ constructor to an initialization function in C.

A::A(int x)
{
  m_x = x;
  m_z = 0;
}

The mapped constructor takes an additional this pointer. A NULL is passed as the this pointer when the object has to be allocated on the heap. A valid stack address is passed when an object is on the stack.

If a NULL pointer is passed to the construction function, it allocates memory before performing the initialization.

A *A_Constructor(A *this_ptr, int x)
{
  /*Check if memory has been allocated for struct A. */
  if (this_ptr == NULL)
  {
    /*Allocate memory of size A. */
    this_ptr = (A *) malloc(sizeof(A));
  }

  /* Once the memory has been allocated for A, initialize members of A. */
  if (this_ptr)
  {
    this_ptr->m_x = x;
    this_ptr->m_z = 0;
  }
  return this_ptr;
}

Complete article: Mapping from C++ classes and methods to C structs and functions.

Destructor representation in C

Destructors also deal with deletion of stack and heap objects.

A::~A()
{
  InformEnd();
}

If the object was allocated on the heap, a boolean is passed to signal to the construction function that the memory was allocated dynamically and needs to be freed.

void A_Destructor(A *this_ptr, BOOLEAN dynamic)
{
  InformEnd(this_ptr);

  /* If the memory was dynamically allocated for A, explicitly free it. */
  if (dynamic)
  {
    free(this_ptr);
  }
}

Complete article: Mapping from C++ classes and methods to C structs and functions.


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LTE Visualization Tool

The LTE Visualization Tool shows the organization of LTE channels in a subcarrier-symbol grid.

You can display:

Signals

LTE Signals

REF, S-SYNC and P-SYNC signals are shown on a subcarrier-symbol grid.

Channels

LTE Channels

PHICH, PDCCH, PBCH and PHICH channels are shown on the subcarrier symbol grid.

Throughput

LTE Throughput and Resource Element Usage

Total count of PDSCH, PBCH, PCFICH, PDCCH channels is shown. The throughout with QPSK, 16QAM and 64QAM is also calculated.

You can configure the:

  • Channel bandwidth
  • Number of antennas
  • Cell identity
  • PHICH duration
  • PHICH group scaling
  • PDCCH Quadruplets

The LTE Visualization Tool may be downloaded for free from:

LTE Visualization Tool