178 lines
4.2 KiB
C++
178 lines
4.2 KiB
C++
/**
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* @file llrand.cpp
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* @brief Global random generator.
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*
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* $LicenseInfo:firstyear=2000&license=viewergpl$
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*
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* Copyright (c) 2000-2009, Linden Research, Inc.
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*
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* Second Life Viewer Source Code
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* The source code in this file ("Source Code") is provided by Linden Lab
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* to you under the terms of the GNU General Public License, version 2.0
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* ("GPL"), unless you have obtained a separate licensing agreement
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* ("Other License"), formally executed by you and Linden Lab. Terms of
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* the GPL can be found in doc/GPL-license.txt in this distribution, or
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* online at http://secondlifegrid.net/programs/open_source/licensing/gplv2
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*
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* There are special exceptions to the terms and conditions of the GPL as
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* it is applied to this Source Code. View the full text of the exception
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* in the file doc/FLOSS-exception.txt in this software distribution, or
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* online at
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* http://secondlifegrid.net/programs/open_source/licensing/flossexception
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*
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* By copying, modifying or distributing this software, you acknowledge
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* that you have read and understood your obligations described above,
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* and agree to abide by those obligations.
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*
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* ALL LINDEN LAB SOURCE CODE IS PROVIDED "AS IS." LINDEN LAB MAKES NO
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* WARRANTIES, EXPRESS, IMPLIED OR OTHERWISE, REGARDING ITS ACCURACY,
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* COMPLETENESS OR PERFORMANCE.
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* $/LicenseInfo$
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*/
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#include "linden_common.h"
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#include "llrand.h"
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#include "lluuid.h"
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/**
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* Through analysis, we have decided that we want to take values which
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* are close enough to 1.0 to map back to 0.0. We came to this
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* conclusion from noting that:
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*
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* [0.0, 1.0)
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*
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* when scaled to the integer set:
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*
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* [0, 4)
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*
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* there is some value close enough to 1.0 that when multiplying by 4,
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* gets truncated to 4. Therefore:
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*
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* [0,1-eps] => 0
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* [1,2-eps] => 1
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* [2,3-eps] => 2
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* [3,4-eps] => 3
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*
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* So 0 gets uneven distribution if we simply clamp. The actual
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* clamp utilized in this file is to map values out of range back
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* to 0 to restore uniform distribution.
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*
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* Also, for clamping floats when asking for a distribution from
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* [0.0,g) we have determined that for values of g < 0.5, then
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* rand*g=g, which is not the desired result. As above, we clamp to 0
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* to restore uniform distribution.
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*/
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// *NOTE: The system rand implementation is probably not correct.
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#define LL_USE_SYSTEM_RAND 0
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#if LL_USE_SYSTEM_RAND
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#include <cstdlib>
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#endif
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#if LL_USE_SYSTEM_RAND
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class LLSeedRand
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{
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public:
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LLSeedRand()
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{
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#if LL_WINDOWS
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srand(LLUUID::getRandomSeed());
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#else
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srand48(LLUUID::getRandomSeed());
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#endif
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}
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};
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static LLSeedRand sRandomSeeder;
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inline F64 ll_internal_random_double()
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{
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#if LL_WINDOWS
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return (F64)rand() / (F64)RAND_MAX;
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#else
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return drand48();
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#endif
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}
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inline F32 ll_internal_random_float()
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{
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#if LL_WINDOWS
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return (F32)rand() / (F32)RAND_MAX;
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#else
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return (F32)drand48();
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#endif
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}
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#else
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static LLRandLagFib2281 gRandomGenerator(LLUUID::getRandomSeed());
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inline F64 ll_internal_random_double()
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{
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// *HACK: Through experimentation, we have found that dual core
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// CPUs (or at least multi-threaded processes) seem to
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// occasionally give an obviously incorrect random number -- like
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// 5^15 or something. Sooooo, clamp it as described above.
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F64 rv = gRandomGenerator();
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if(!((rv >= 0.0) && (rv < 1.0))) return fmod(rv, 1.0);
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return rv;
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}
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inline F32 ll_internal_random_float()
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{
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// The clamping rules are described above.
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F32 rv = (F32)gRandomGenerator();
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if(!((rv >= 0.0f) && (rv < 1.0f))) return fmod(rv, 1.f);
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return rv;
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}
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#endif
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S32 ll_rand()
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{
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return ll_rand(RAND_MAX);
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}
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S32 ll_rand(S32 val)
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{
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// The clamping rules are described above.
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S32 rv = (S32)(ll_internal_random_double() * val);
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if(rv == val) return 0;
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return rv;
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}
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F32 ll_frand()
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{
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return ll_internal_random_float();
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}
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F32 ll_frand(F32 val)
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{
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// The clamping rules are described above.
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F32 rv = ll_internal_random_float() * val;
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if(val > 0)
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{
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if(rv >= val) return 0.0f;
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}
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else
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{
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if(rv <= val) return 0.0f;
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}
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return rv;
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}
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F64 ll_drand()
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{
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return ll_internal_random_double();
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}
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F64 ll_drand(F64 val)
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{
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// The clamping rules are described above.
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F64 rv = ll_internal_random_double() * val;
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if(val > 0)
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{
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if(rv >= val) return 0.0;
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}
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else
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{
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if(rv <= val) return 0.0;
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}
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return rv;
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}
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