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/**
* @file llrand.cpp
* @brief Global random generator.
*
* Copyright (c) 2000-2007, Linden Research, Inc.
*
* 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://secondlife.com/developers/opensource/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://secondlife.com/developers/opensource/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.
*/
#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.
*/
// *NOTE: The system rand implementation is probably not correct.
#define LL_USE_SYSTEM_RAND 0
#if LL_USE_SYSTEM_RAND
#include <stdlib.h>
#endif
#if LL_USE_SYSTEM_RAND
class LLSeedRand
{
public:
LLSeedRand()
{
#if LL_WINDOWS
srand(LLUUID::getRandomSeed());
#else
srand48(LLUUID::getRandomSeed());
#endif
}
};
static LLSeedRand sRandomSeeder;
inline F64 ll_internal_random_double()
{
#if LL_WINDOWS
return (F64)rand() / (F64)RAND_MAX;
#else
return drand48();
#endif
}
inline F32 ll_internal_random_float()
{
#if LL_WINDOWS
return (F32)rand() / (F32)RAND_MAX;
#else
return (F32)drand48();
#endif
}
#else
static LLRandLagFib2281 gRandomGenerator(LLUUID::getRandomSeed());
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 0.0;
return rv;
}
inline F32 ll_internal_random_float()
{
// The clamping rules are described above.
F32 rv = (F32)gRandomGenerator();
if(!((rv >= 0.0f) && (rv < 1.0f))) return 0.0f;
return rv;
}
#endif
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;
}
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 0.0f;
}
else
{
if(rv <= val) return 0.0f;
}
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;
}
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