// ---------------------------------------------------------------------
// precise_time.cxx
//
// Copyright (C) 2023
//		Dave Freese, W1HKJ
//
// This file is part of flrig
//
// flrig is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// flrig is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with fldigi.  If not, see <http://www.gnu.org/licenses/>.
// ---------------------------------------------------------------------

#include <errno.h>
#include <time.h>
#include <sys/time.h>

#if 0
// return current tick time in seconds
double monotonic_seconds()
{
	static struct timeval t1;
	gettimeofday(&t1, NULL);
	return t1.tv_sec + t1.tv_usec / 1e6;
}

#else

//======================================================================
//
// A cross platform monotonic timer.
// Copyright 2013 Alex Reece.
//

#include <unistd.h>

#define NANOS_PER_SECF 1000000000.0
#define USECS_PER_SEC 1000000

static int showme = 0;

#if _POSIX_TIMERS > 0 && defined(_POSIX_MONOTONIC_CLOCK)
	// If we have it, use clock_gettime and CLOCK_MONOTONIC.

	#include <time.h>

	double monotonic_seconds() {
		if (showme) {
			showme = 0;
		}
		struct timespec time;
		// Note: Make sure to link with -lrt to define clock_gettime.
		clock_gettime(CLOCK_MONOTONIC, &time);
		return ((double) time.tv_sec) + ((double) time.tv_nsec / (NANOS_PER_SECF));
	}

#elif defined(__APPLE__)
	// If we don't have CLOCK_MONOTONIC, we might be on a Mac. There we instead
	// use mach_absolute_time().

	#include <mach/mach_time.h>

	static mach_timebase_info_data_t info;
	static void __attribute__((constructor)) init_info() {
		mach_timebase_info(&info);
	}

	double monotonic_seconds() {
		uint64_t time = mach_absolute_time();
		double dtime = (double) time;
		dtime *= (double) info.numer;
		dtime /= (double) info.denom;
		return dtime / NANOS_PER_SECF;
	}

#elif defined(__WIN32__)
	// On Windows, use QueryPerformanceCounter and QueryPerformanceFrequency.

	#include <windows.h>

	static double PCFreq = 0.0;

	// According to http://stackoverflow.com/q/1113409/447288, this will
	// make this function a constructor.
	// TODO(awreece) Actually attempt to compile on windows.
	// w1hkj - builds OK on mingw32

	static void __cdecl init_pcfreq();
	__declspec(allocate(".CRT$XCU")) void (__cdecl*init_pcfreq_)() = init_pcfreq;
	static void __cdecl init_pcfreq() {
		// Accoring to http://stackoverflow.com/a/1739265/447288, this will
		// properly initialize the QueryPerformanceCounter.
		LARGE_INTEGER li;
		int has_qpc = QueryPerformanceFrequency(&li);
		assert(has_qpc);

		PCFreq = ((double) li.QuadPart) / 1000.0;
	}

	double monotonic_seconds() {
		LARGE_INTEGER li;
		QueryPerformanceCounter(&li);
		return ((double) li.QuadPart) / PCFreq;
	}

#else
	// Fall back to rdtsc. The reason we don't use clock() is this scary message
	// from the man page:
	//     "On several other implementations, the value returned by clock() also
	//      includes the times of any children whose status has been collected via
	//      wait(2) (or another wait-type call)."
	//
	// Also, clock() only has microsecond accuracy.
	//
	// This whitepaper offered excellent advice on how to use rdtscp for
	// profiling: http://download.intel.com/embedded/software/IA/324264.pdf
	//
	// Unfortunately, we can't follow its advice exactly with our semantics,
	// so we're just going to use rdtscp with cpuid.
	//
	// Note that rdtscp will only be available on new processors.

	#include <stdint.h>

	static inline uint64_t rdtsc() {
		uint32_t hi, lo;
		asm volatile("rdtscp\n"
								 "movl %%edx, %0\n"
								 "movl %%eax, %1\n"
								 "cpuid"
								 : "=r" (hi), "=r" (lo) : : "%rax", "%rbx", "%rcx", "%rdx");
		return (((uint64_t)hi) << 32) | (uint64_t)lo;
	}

	static uint64_t rdtsc_per_sec = 0;
	static void __attribute__((constructor)) init_rdtsc_per_sec() {
		uint64_t before, after;

		before = rdtsc();
		usleep(USECS_PER_SEC);
		after = rdtsc();

		rdtsc_per_sec = after - before;
	}

	double monotonic_seconds() {
		if (showme) {
			showme = false;
		}
		return (double) rdtsc() / (double) rdtsc_per_sec;
	}

#endif

#endif
