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Measuring execution time of a function.
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| #include <stdio.h> | |
| volatile int tmp; | |
| static const int N = 123456789; | |
| /* Linux method #0: use gettimeofday() (obsolete?) | |
| */ | |
| #include <sys/time.h> | |
| // timeradd, timersub, etc. macros are _BSD_SOURCE. | |
| // Those will be defined only if the symbol __USE_BSD is defined. | |
| #ifndef timersub | |
| #define timersub(a, b, result) \ | |
| do { \ | |
| (result)->tv_sec = (a)->tv_sec - (b)->tv_sec; \ | |
| (result)->tv_usec = (a)->tv_usec - (b)->tv_usec; \ | |
| if ((result)->tv_usec < 0) { \ | |
| --(result)->tv_sec; \ | |
| (result)->tv_usec += 1000000; \ | |
| } \ | |
| } while (0) | |
| #endif // timersub | |
| void linux_method0(void) | |
| { | |
| struct timeval time0, time1, time_diff; | |
| // start time | |
| gettimeofday(&time0, NULL); | |
| // do something | |
| int i; | |
| for (i = 0; i < N; ++i) { | |
| tmp = i; | |
| } | |
| // finish time | |
| gettimeofday(&time1, NULL); | |
| // print elapsed time | |
| timersub(&time1, &time0, &time_diff); | |
| printf("Elapsed time: %ld.%06ld s\n", | |
| time_diff.tv_sec, time_diff.tv_usec); | |
| } | |
| /* Linux method #1: use clock_gettime() | |
| * Compile with -std=gnu99 | |
| * Link with -lrt (glibc <2.17) | |
| */ | |
| #include <time.h> | |
| #define timespec_sub(a, b, result) \ | |
| do { \ | |
| (result)->tv_sec = (a)->tv_sec - (b)->tv_sec; \ | |
| (result)->tv_nsec = (a)->tv_nsec - (b)->tv_nsec; \ | |
| if ((result)->tv_nsec < 0) { \ | |
| --(result)->tv_sec; \ | |
| (result)->tv_nsec += 1000000000; \ | |
| } \ | |
| } while (0) | |
| void linux_method1(void) | |
| { | |
| struct timespec time0, time1, time_diff; | |
| // start time | |
| clock_gettime(CLOCK_REALTIME, &time0); | |
| // do something | |
| int i; | |
| for (i = 0; i < N; ++i) { | |
| tmp = i; | |
| } | |
| // finish time | |
| clock_gettime(CLOCK_REALTIME, &time1); | |
| // print elapsed time | |
| timespec_sub(&time1, &time0, &time_diff); | |
| printf("Elapsed time: %ld.%09ld s\n", | |
| time_diff.tv_sec, time_diff.tv_nsec); | |
| } | |
| /* Windows method #0 | |
| */ | |
| #include <windows.h> | |
| void windows_method0(void) | |
| { | |
| LARGE_INTEGER li; | |
| __int64 CounterStart = 0; | |
| if (!QueryPerformanceFrequency(&li)) | |
| printf("QueryPerformanceFrequency failed\n"); | |
| double PCFreq = (double) li.QuadPart; | |
| // start time | |
| QueryPerformanceCounter(&li); | |
| CounterStart = li.QuadPart; | |
| // do something | |
| int i; | |
| for (i = 0; i < N; ++i) { | |
| tmp = i; | |
| } | |
| // finish time | |
| QueryPerformanceCounter(&li); | |
| printf("Elapsed time: %.6f s\n", | |
| ((double) (li.QuadPart - CounterStart)) / PCFreq); | |
| } | |
| int main() | |
| { | |
| linux_method0(); | |
| linux_method1(); | |
| windows_method0(); | |
| return 0; | |
| } |
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