/**
 * @file llrand.cpp
 * @brief Global random generator.
 *
 * $LicenseInfo:firstyear=2000&license=viewergpl$
 *
 * Copyright (c) 2000-2009, Linden Research, Inc.
 *
 * Second Life Viewer Source Code
 * The source code in this file ("Source Code") is provided by Linden Lab
 * to you under the terms of the GNU General Public License, version 2.0
 * ("GPL"), unless you have obtained a separate licensing agreement
 * ("Other License"), formally executed by you and Linden Lab.  Terms of
 * the GPL can be found in doc/GPL-license.txt in this distribution, or
 * online at http://secondlifegrid.net/programs/open_source/licensing/gplv2
 *
 * There are special exceptions to the terms and conditions of the GPL as
 * it is applied to this Source Code. View the full text of the exception
 * in the file doc/FLOSS-exception.txt in this software distribution, or
 * online at
 * http://secondlifegrid.net/programs/open_source/licensing/flossexception
 *
 * By copying, modifying or distributing this software, you acknowledge
 * that you have read and understood your obligations described above,
 * and agree to abide by those obligations.
 *
 * ALL LINDEN LAB SOURCE CODE IS PROVIDED "AS IS." LINDEN LAB MAKES NO
 * WARRANTIES, EXPRESS, IMPLIED OR OTHERWISE, REGARDING ITS ACCURACY,
 * COMPLETENESS OR PERFORMANCE.
 * $/LicenseInfo$
 */

#if !LL_WINDOWS
# include <unistd.h>			// For getpid()
#endif

#include "linden_common.h"

#include "llrand.h"

#include "llsys.h"				// For LLOSInfo::getNodeID()
#include "hbxxh.h"

// Used to be LLUUID::getRandomSeed(), but only in use here, so... HB
static U32 get_random_seed()
{
	static unsigned char seed[16];
	static bool init_done = false;
	if (!init_done)
	{
		init_done = true;
		LLOSInfo::getNodeID(&seed[0]);

		// Incorporate the pid into the seed to prevent processes that start
		// on the same host at the same time from generating the same seed.
#if LL_WINDOWS
		int pid = GetCurrentProcessId();
#else
		int pid = getpid();
#endif
		seed[6] = (unsigned char)(pid >> 8);
		seed[7] = (unsigned char)(pid);
	}

	LLUUID::getSystemTime((uuid_time_t*)(&seed[8]));
	return digest64to32(HBXXH64::digest((const void*)seed, 16));
}

/**
 * Through analysis, we have decided that we want to take values which
 * are close enough to 1.0 to map back to 0.0.  We came to this
 * conclusion from noting that:
 *
 * [0.0, 1.0)
 *
 * when scaled to the integer set:
 *
 * [0, 4)
 *
 * there is some value close enough to 1.0 that when multiplying by 4,
 * gets truncated to 4. Therefore:
 *
 * [0,1-eps] => 0
 * [1,2-eps] => 1
 * [2,3-eps] => 2
 * [3,4-eps] => 3
 *
 * So 0 gets uneven distribution if we simply clamp. The actual
 * clamp utilized in this file is to map values out of range back
 * to 0 to restore uniform distribution.
 *
 * Also, for clamping floats when asking for a distribution from
 * [0.0,g) we have determined that for values of g < 0.5, then
 * rand*g=g, which is not the desired result. As above, we clamp to 0
 * to restore uniform distribution.
 */

#if LL_USE_SYSTEM_RAND

# include <cstdlib>

class LLSeedRand
{
public:
	LLSeedRand()
	{
#if LL_WINDOWS
		srand(get_random_seed());
#else
		srand48(get_random_seed());
#endif
	}
};

static LLSeedRand sRandomSeeder;
static LL_INLINE F64 ll_internal_random_double()
{
# if LL_WINDOWS
	return (F64)rand() / (F64)RAND_MAX;
# else
	return drand48();
# endif
}

static LL_INLINE F32 ll_internal_random_float()
{
# if LL_WINDOWS
	return (F32)rand() / (F32)RAND_MAX;
# else
	return (F32)drand48();
# endif
}

#else	// LL_USE_SYSTEM_RAND

// Work around bogus deprecated header warning in boost v1.69...
# ifndef BOOST_ALLOW_DEPRECATED_HEADERS
#  define BOOST_ALLOW_DEPRECATED_HEADERS 1
# endif
# include "boost/random/lagged_fibonacci.hpp"
# undef BOOST_ALLOW_DEPRECATED_HEADERS

static boost::lagged_fibonacci2281 gRandomGenerator(get_random_seed());
static LL_INLINE F64 ll_internal_random_double()
{
	// *HACK: through experimentation, we have found that dual core CPUs (or at
	// least multi-threaded processes) seem to occasionally give an obviously
	// incorrect random number -- like 5^15 or something. Sooooo, clamp it as
	// described above.
	F64 rv = gRandomGenerator();
	if (rv < 0.0 || rv >= 1.0)
	{
		return fmod(rv, 1.0);
	}
	return rv;
}

static LL_INLINE F32 ll_internal_random_float()
{
	// The clamping rules are described above.
	F32 rv = (F32)gRandomGenerator();
	if (rv < 0.f || rv >= 1.f)
	{
		return fmodf(rv, 1.f);
	}
	return rv;
}

#endif	// LL_USE_SYSTEM_RAND

S32 ll_rand()
{
	return ll_rand(RAND_MAX);
}

S32 ll_rand(S32 val)
{
	// The clamping rules are described above.
	S32 rv = (S32)(ll_internal_random_double() * F64(val));
	return rv == val ? 0 : rv;
}

F32 ll_frand()
{
	return ll_internal_random_float();
}

F32 ll_frand(F32 val)
{
	// The clamping rules are described above.
	F32 rv = ll_internal_random_float() * val;
	if (val > 0)
	{
		if (rv >= val)
		{
			return 0.f;
		}
	}
	else if (rv <= val)
	{
		return 0.f;
	}
	return rv;
}

F64 ll_drand()
{
	return ll_internal_random_double();
}

F64 ll_drand(F64 val)
{
	// The clamping rules are described above.
	F64 rv = ll_internal_random_double() * val;
	if (val > 0)
	{
		if (rv >= val)
		{
			return 0.0;
		}
	}
	else if (rv <= val)
	{
		return 0.0;
	}
	return rv;
}