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/**
* @file llrand.cpp
* @brief Global random generator.
*
* $LicenseInfo:firstyear=2000&license=viewerlgpl$
* Second Life Viewer Source Code
* Copyright (C) 2010, Linden Research, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation;
* version 2.1 of the License only.
*
* This library 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*
* Linden Research, Inc., 945 Battery Street, San Francisco, CA 94111 USA
* $/LicenseInfo$
*/
#include "linden_common.h"
#include "llrand.h"
#include "lluuid.h"
/**
* 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.
*/
// gRandomGenerator is a stateful static object, which is therefore not
// inherently thread-safe.
static thread_local LLRandLagFib2281 gRandomGenerator(LLUUID::getRandomSeed());
// no default implementation, only specific F64 and F32 specializations
template <typename REAL>
inline REAL ll_internal_random();
template <>
inline F64 ll_internal_random<F64>()
{
// *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;
}
template <>
inline F32 ll_internal_random<F32>()
{
// *HACK: clamp the result as described above.
// Per Monty, it's important to clamp using the correct fmodf() rather
// than expanding to F64 for fmod() and then truncating back to F32. Prior
// to this change, we were getting sporadic ll_frand() == 1.0 results.
F32 rv{ narrow<F64>(gRandomGenerator()) };
if(!((rv >= 0.0f) && (rv < 1.0f))) return fmodf(rv, 1.0f);
return rv;
}
/*------------------------------ F64 aliases -------------------------------*/
inline F64 ll_internal_random_double()
{
return ll_internal_random<F64>();
}
F64 ll_drand()
{
return ll_internal_random_double();
}
/*------------------------------ F32 aliases -------------------------------*/
inline F32 ll_internal_random_float()
{
return ll_internal_random<F32>();
}
F32 ll_frand()
{
return ll_internal_random_float();
}
/*-------------------------- clamped random range --------------------------*/
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() * val);
if(rv == val) return 0;
return rv;
}
template <typename REAL>
REAL ll_grand(REAL val)
{
// The clamping rules are described above.
REAL rv = ll_internal_random<REAL>() * val;
if(val > 0)
{
if(rv >= val) return REAL();
}
else
{
if(rv <= val) return REAL();
}
return rv;
}
F32 ll_frand(F32 val)
{
return ll_grand<F32>(val);
}
F64 ll_drand(F64 val)
{
return ll_grand<F64>(val);
}
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