fasttime.h

/**
 * Copyright (c) 2014 MIT License by 6.172 Staff
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to
 * deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 **/

#ifndef INCLUDED_FASTTIME_DOT_H
#define INCLUDED_FASTTIME_DOT_H

#define _POSIX_C_SOURCE 200809L

#include <assert.h>

#ifdef __MACH__
#include <mach/mach_time.h>  // mach_absolute_time

typedef uint64_t fasttime_t;


// Return the current time.
static inline fasttime_t gettime(void) {
  return mach_absolute_time();
}

// Return the time different between the start and the end, as a float
// in units of seconds.  This function does not need to be fast.
// Implementation notes: See
// https://developer.apple.com/library/mac/qa/qa1398/_index.html
static inline double tdiff(fasttime_t start, fasttime_t end) {
  static mach_timebase_info_data_t timebase;
  int r = mach_timebase_info(&timebase);
  assert(r == 0);
  fasttime_t elapsed = end-start;
  double ns = (double)elapsed * timebase.numer / timebase.denom;
  return ns*1e-9;
}

static inline unsigned int random_seed_from_clock(void) {
  fasttime_t now = gettime();
  return (now & 0xFFFFFFFF) + (now>>32);
}

#else  // LINUX

// We need _POSIX_C_SOURCE to pick up 'struct timespec' and clock_gettime.
// #define _POSIX_C_SOURCE 200809L

#include <time.h>

typedef struct timespec fasttime_t;

// Return the current time.
static inline fasttime_t gettime(void) {
  struct timespec s;
#ifdef NDEBUG
  clock_gettime(CLOCK_MONOTONIC, &s);
#else
  int r = clock_gettime(CLOCK_MONOTONIC, &s);
  assert(r == 0);
#endif
  return s;
}

// Return the time different between the start and the end, as a float
// in units of seconds.  This function does not need to be fast.
static inline double tdiff(fasttime_t start, fasttime_t end) {
  return end.tv_sec - start.tv_sec + 1e-9*(end.tv_nsec - start.tv_nsec);
}

static inline unsigned int random_seed_from_clock(void) {
  fasttime_t now = gettime();
  return now.tv_sec + now.tv_nsec;
}

// Poison these symbols to help find portability problems.
int clock_gettime(clockid_t, struct timespec *) __attribute__((deprecated));
time_t time(time_t *) __attribute__((deprecated));

#endif  // LINUX

#endif  // INCLUDED_FASTTIME_DOT_H