timer.h

#include <stdio.h>
#include <stdint.h>

#if defined(__APPLE__)
    #include <mach/mach_time.h>
#elif defined(_WIN32)
    #include <windows.h>
#else
    #ifdef _POSIX_C_SOURCE
        #define NS_OLD_POSIX_C_SOURCE _POSIX_C_SOURCE
        #undef _POSIX_C_SOURCE
    #endif
    #define _POSIX_C_SOURCE 199309L
    #ifndef __USE_POSIX199309
        #define __USE_POSIX199309
        #define NS_DEFINED__USE_POSIX199309
    #endif
    #include <time.h>
    #ifdef NS_DEFINED__USE_POSIX199309
        #undef __USE_POSIX199309
    #endif
    #ifdef NS_OLD_POSIX_C_SOURCE
        #undef _POSIX_C_SOURCE
        #define _POSIX_C_SOURCE NS_OLD_POSIX_C_SOURCE
    #endif
    #ifdef CLOCK_MONOTONIC
        #define NS_CLOCK_ID CLOCK_MONOTONIC
    #else
        #define NS_CLOCK_ID CLOCK_REALTIME
    #endif
#endif

static inline uint64_t ns(void) {
    static uint8_t ns_inited = 0;
    #if defined(__APPLE__)
        static mach_timebase_info_data_t info;
        uint64_t now;
        if (ns_inited == 0) {
            mach_timebase_info(&info);
            ns_inited = 1;
        }
        now = mach_absolute_time();
        now *= info.numer;
        now /= info.denom;
        return now;
    #elif defined(_WIN32)
        static LARGE_INTEGER win_frequency;
        LARGE_INTEGER now;
        if (ns_inited == 0) {
            QueryPerformanceFrequency(&win_frequency);
            ns_inited = 1;
        }
        QueryPerformanceCounter(&now);
        return (uint64_t)((1.0e9 * now.QuadPart) / win_frequency.QuadPart);
    #else
        static struct timespec linux_rate;
        uint64_t now;
        struct timespec spec;
        if (ns_inited == 0) {
            clock_getres(NS_CLOCK_ID, &linux_rate);
            ns_inited = 1;
        }
        clock_gettime(NS_CLOCK_ID, &spec);
        now = spec.tv_sec * (uint64_t)1.0e9 + spec.tv_nsec;
        return now;
    #endif
}

// Define a struct to hold the start and end times and the duration
typedef struct Timer {
    uint64_t start_time;
    uint64_t end_time;
    double duration;
} Timer;

static inline void timer_start(Timer *timer) {
    timer->start_time = ns();
}

static inline  void timer_end(Timer *timer) {
    timer->end_time = ns();
    timer->duration = (timer->end_time - timer->start_time);
}