//========= Copyright 1996-2005, Valve Corporation, All rights reserved. ============//
//
// Purpose: determine CPU speed under linux
//
// $NoKeywords: $
//=============================================================================//
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/sysctl.h>
#include <sys/time.h>
#include <unistd.h>
#include <tier0/platform.h>
#include <errno.h>

class TimeVal
{
public:
	TimeVal() {}
	TimeVal& operator=(const TimeVal &val) { m_TimeVal = val.m_TimeVal; return *this; }
	inline double operator-(const TimeVal &left)
	{
		uint64 left_us = (uint64) left.m_TimeVal.tv_sec * 1000000 + left.m_TimeVal.tv_usec;
		uint64 right_us = (uint64) m_TimeVal.tv_sec * 1000000 + m_TimeVal.tv_usec;
		uint64 diff_us = right_us - left_us;
		return diff_us * ( 1.0 / 1000000.0 );
	}

	timeval m_TimeVal;
};

// Compute the positive difference between two 64 bit numbers.
static inline uint64 diff(uint64 v1, uint64 v2)
{
	//  uint64 d = v1 - v2;
	//  if (d >= 0) return d; else return -d;
	return (v1 >= v2 ? v1 - v2 : v2 - v1);
}

#ifdef OSX
uint64 GetCPUFreqFromPROC()
{
        int mib[2] = {CTL_HW, HW_CPU_FREQ};
        uint64 frequency = 0;
        size_t len = sizeof(frequency);

        if (sysctl(mib, 2, &frequency, &len, NULL, 0) == -1)
                return 0;
        return frequency;
}
#else
uint64 GetCPUFreqFromPROC()
{
	double mhz = 0;
	char line[1024], *s, search_str[] = "cpu MHz";
	FILE *fp;

	/* open proc/cpuinfo */
	if ((fp = fopen("/proc/cpuinfo", "r")) == NULL)
	{
		return 0;
	}

	/* ignore all lines until we reach MHz information */
	while (fgets(line, 1024, fp) != NULL)
	{
		if (strstr(line, search_str) != NULL)
		{
			/* ignore all characters in line up to : */
			for (s = line; *s && (*s != ':'); ++s)
				;

			/* get MHz number */
			if (*s && (sscanf(s+1, "%lf", &mhz) == 1))
				break;
		}
	}

	if (fp!=NULL) fclose(fp);

	return (uint64)(mhz*1000000);
}
#endif


uint64 CalculateCPUFreq()
{
#ifdef LINUX
	char const *pFreq = getenv("CPU_MHZ");
	if ( pFreq )
	{
		uint64 retVal = 1000000;
		return retVal * atoi( pFreq );
	}
#endif

	// Compute the period. Loop until we get 3 consecutive periods that
	// are the same to within a small error. The error is chosen
	// to be +/- 0.02% on a P-200.
	const uint64 error = 40000;
	const int max_iterations = 600;
	int count;
	uint64 period, period1 = error * 2, period2 = 0,  period3 = 0;

	for (count = 0; count < max_iterations; count++)
	{
		TimeVal start_time, end_time;
		uint64 start_tsc, end_tsc;

		gettimeofday( &start_time.m_TimeVal, 0 );
		start_tsc = Plat_Rdtsc();
		usleep( 5000 ); // sleep for 5 msec
		gettimeofday( &end_time.m_TimeVal, 0 );
		end_tsc = Plat_Rdtsc();

		period3 = ( end_tsc - start_tsc ) / ( end_time - start_time );

		if (diff( period1, period2 ) <= error &&
			diff( period2, period3 ) <= error &&
			diff( period1, period3 ) <= error )
		{
			break;
		}

		period1 = period2;
		period2 = period3;
	}

	if ( count == max_iterations )
	{
		return GetCPUFreqFromPROC(); // fall back to /proc
	}

	// Set the period to the average period measured.
	period = ( period1 + period2 + period3 ) / 3;

	// Some Pentiums have broken TSCs that increment very
	// slowly or unevenly.
	if ( period < 10000000 )
	{
		return GetCPUFreqFromPROC(); // fall back to /proc
	}

	return period;
}