Portable higher-resolution timer with nanosecond granularity.

timer.c

/* ----------------------------------------------------------------------- */
/*
  Easy embeddable cross-platform high resolution timer function. For each 
  platform we select the high resolution timer. You can call the 'ns()' 
  function in your file after embedding this. 
  
  https://www.roxlu.com/2014/047/high-resolution-timer-function-in-c-c--
*/
#include <stdint.h>
#if defined(__linux)
#  define HAVE_POSIX_TIMER
#  include <time.h>
#  ifdef CLOCK_MONOTONIC
#     define CLOCKID CLOCK_MONOTONIC
#  else
#     define CLOCKID CLOCK_REALTIME
#  endif
#elif defined(__APPLE__)
#  define HAVE_MACH_TIMER
#  include <mach/mach_time.h>
#elif defined(_WIN32)
#  define WIN32_LEAN_AND_MEAN
#  include <windows.h>
#endif
static uint64_t ns() {
  static uint64_t is_init = 0;
#if defined(__APPLE__)
    static mach_timebase_info_data_t info;
    if (0 == is_init) {
      mach_timebase_info(&info);
      is_init = 1;
    }
    uint64_t now;
    now = mach_absolute_time();
    now *= info.numer;
    now /= info.denom;
    return now;
#elif defined(__linux)
    static struct timespec linux_rate;
    if (0 == is_init) {
      clock_getres(CLOCKID, &linux_rate);
      is_init = 1;
    }
    uint64_t now;
    struct timespec spec;
    clock_gettime(CLOCKID, &spec);
    now = spec.tv_sec * 1.0e9 + spec.tv_nsec;
    return now;
#elif defined(_WIN32)
    static LARGE_INTEGER win_frequency;
    if (0 == is_init) {
      QueryPerformanceFrequency(&win_frequency);
      is_init = 1;
    }
    LARGE_INTEGER now;
    QueryPerformanceCounter(&now);
    return (uint64_t) ((1e9 * now.QuadPart)  / win_frequency.QuadPart);
#endif
}
/* ----------------------------------------------------------------------- */