/indra/llcommon/llrand.cpp
C++ | 171 lines | 96 code | 13 blank | 62 comment | 12 complexity | a6c17e933cd22997caebaa5443e5fbe9 MD5 | raw file
Possible License(s): LGPL-2.1
- /**
- * @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.
- */
- // *NOTE: The system rand implementation is probably not correct.
- #define LL_USE_SYSTEM_RAND 0
- #if LL_USE_SYSTEM_RAND
- #include <cstdlib>
- #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 fmod(rv, 1.0);
- 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 fmod(rv, 1.f);
- 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;
- }