How Can I Achieve Nanoscale Time Measurement in C ?

C Timer Function for Nanosecond Time Measurement

Measuring execution time in nanoscale precision with a C class function requires a timer that offers higher accuracy than the default clock_t implementation.

The provided code utilizes the clock_t type to measure time in seconds. For nanoscale precision, you need an alternative timer implementation.

Linux (and BSD)

Use clock_gettime():

#include <sys/time.h>

int main() {
    timespec ts;
    clock_gettime(CLOCK_REALTIME, &ts);
    return 0;
}

Windows

Use QueryPerformanceCounter:

#include <windows.h>

int main() {
    LARGE_INTEGER freq, pc;
    QueryPerformanceFrequency(&freq);
    QueryPerformanceCounter(&pc);
    return 0;
}

Additional Considerations:

• QueryPerformanceCounter can occasionally return anomalous readings on certain chipsets.
• Windows 7 and later can detect if processors have an invariant TSC and switch to an external timer if necessary. However, processor synchronization remains a challenge.

References:

• [clock_gettime](https://linux.die.net/man/3/clock_gettime)
• [QueryPerformanceCounter](https://docs.microsoft.com/en-us/windows/win32/api/profileapi/nf-profileapi-queryperformancecounter)
• [High-Resolution Clocks and Timers for Windows](http://performancebydesign.blogspot.com/2012/03/high-resolution-clocks-and-timers-for.html)

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