How Can I Accurately Measure the Execution Time of a C Code Snippet?

How to Calculate Execution Time of a Code Snippet Accurately in C

Measuring the execution time of a code snippet is crucial when optimizing code performance. This article explores how to effectively calculate the execution time of a C code snippet, ensuring accuracy even for short statements or small inputs.

Limitations of Clock:

The clock() function, despite being widely used, has limitations when measuring short durations. It returns the CPU time consumed by the process, which can be coarse and yield "0 seconds" results for brief tasks.

Solution: Using GetTimeMs64() Function:

To overcome these limitations, the GetTimeMs64() function provides a more precise measurement of elapsed time. It utilizes the system clock on both Windows and Linux, delivering accurate results even for minute durations.

Implementation Details:

The GetTimeMs64() function obtains the number of milliseconds since the UNIX epoch. It works by:

• Windows:

  • Retrieves the system time as a FILETIME and converts it to a LARGE_INTEGER structure.
  • Adjusts the result to match the UNIX epoch time in milliseconds.

• Linux:

  • Acquires the current time using gettimeofday().
  • Converts the microseconds value to milliseconds.
  • Adds the seconds value, also converted to milliseconds.

Usage:

To measure the execution time of a code snippet using the GetTimeMs64() function:

1. Include the GetTimeMs64.h header file.
2. Call GetTimeMs64() before executing the code snippet.
3. Call GetTimeMs64() again after the code snippet completes execution.
4. Calculate the elapsed time by subtracting the initial time from the final time.

Advantages of GetTimeMs64() Function:

• Precision: Provides more accurate results, especially for short durations.
• Cross-Platform: Works effectively on both Windows and Linux systems.
• Thread Safety: Safe to use within multi-threaded environments.

Considerations:

• The time granularity for GetTimeMs64() is typically 15 ms on Windows and may vary on Linux.
• This function measures elapsed wall-clock time, which may include system-related delays.

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