How does C++ optimize code performance on embedded devices?

Guidelines for performance optimization of C code on embedded devices: Code size optimization: Disable debug symbols Static linking Remove unreferenced code Use inline functions Execution speed optimization: Use optimizing compiler optimization algorithms Leverage assembly optimization to reduce dynamic memory allocation

A guide to optimizing the performance of C code on embedded devices

Introduction
In Embedded Systems , optimizing code performance is critical to making full use of limited resources. By applying specific techniques, you can significantly reduce code size and increase execution speed. This article will explore some practical tips and tricks to optimize C code performance on embedded devices.

Code size optimization

• Disable debugging symbols: During the compilation process, disabling debugging symbols can significantly reduce the size of the executable file size.
• Static linking: Compared to dynamic link libraries, static linking packages code and dependencies into a single executable file, thereby reducing file size.
• Remove Unreferenced Code: Use linker options to remove unreferenced code and symbols to further reduce executable size.
• Use inline functions: Inline frequently called functions to avoid the overhead of function calls.

Execution speed optimization

• Use an optimizing compiler: Use a compiler optimized for a specific architecture, such as GCC or Clang, which generates faster code.
• Optimization algorithm: Select algorithms suitable for embedded systems that achieve the same function with lower complexity.
• Take advantage of assembly optimization: For performance-critical sections, converting C code to assembly code can further increase execution speed.
• Reduce dynamic memory allocation: Dynamic memory allocation introduces overhead. Try to use static memory allocation or memory pools to improve performance.

Practical Case

Consider the following example, where an optimized version converts a string from uppercase to lowercase:

// 未经优化的版本
void toLower(char* str) {
  while (*str) {
    if (*str >= 'A' && *str <= 'Z') {
      *str += 32;
    }
    str++;
  }
}

// 优化的版本
void toLowerOpt(char* str) {
  asm("1:");
  cmp byte ptr [rsi], 0
  je 3f
  cmp byte ptr [rsi], 'A'
  jb 1b
  cmp byte ptr [rsi], 'Z'
  ja 1b
  add byte ptr [rsi], 32
  2:
  inc rsi
  jmp 1b
  3:
  ret
}

In In the assembly-optimized version, unnecessary checks are removed and register operations are used, thereby improving execution speed.

Conclusion
By applying these optimization techniques, C code performance on embedded devices can be significantly improved. Through planning and attention to detail, developers can create fast and efficient code that takes full advantage of the limited resources of embedded systems.

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