Imported existing code

indra/llcommon/llrand.cpp

@@ -0,0 +1,177 @@
+/** 
+ * @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.
+ * $/LicenseInfo$
+ */
+
+#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;
+}