Added the cFastRandom class

git-svn-id: http://mc-server.googlecode.com/svn/trunk@1672 0a769ca7-a7f5-676a-18bf-c427514a06d6

VC2008/MCServer.vcproj

@@ -402,6 +402,14 @@
 				RelativePath="..\source\Endianness.h"
 				>
 			</File>
+			<File
+				RelativePath="..\source\FastRandom.cpp"
+				>
+			</File>
+			<File
+				RelativePath="..\source\FastRandom.h"
+				>
+			</File>
 			<File
 				RelativePath="..\source\FurnaceRecipe.cpp"
 				>

source/FastRandom.cpp

@@ -0,0 +1,174 @@
+
+// FastRandom.cpp
+
+// Implements the cFastRandom class representing a fast random number generator
+
+#include "Globals.h"
+#include <time.h>
+#include "FastRandom.h"
+
+
+
+
+
+#if 0 && defined(_DEBUG)
+// Self-test
+// Both ints and floats are quick-tested to see if the random is calculated correctly, checking the range in ASSERTs,
+// and if it performs well in terms of distribution (checked by avg, expected to be in the range midpoint
+class cFastRandomTest
+{
+public:
+	cFastRandomTest(void)
+	{
+		TestInts();
+		TestFloats();
+	}
+	
+	
+	void TestInts(void)
+	{
+		printf("Testing ints...\n");
+		cFastRandom rnd;
+		int sum = 0;
+		const int BUCKETS = 8;
+		int Counts[BUCKETS];
+		memset(Counts, 0, sizeof(Counts));
+		const int ITER = 10000;
+		for (int i = 0; i < ITER; i++)
+		{
+			int v = rnd.NextInt(1000);
+			ASSERT(v >= 0);
+			ASSERT(v < 1000);
+			Counts[v % BUCKETS]++;
+			sum += v;
+		}
+		double avg = (double)sum / ITER;
+		printf("avg: %f\n", avg);
+		for (int i = 0; i < BUCKETS; i++)
+		{
+			printf("  bucket %d: %d\n", i, Counts[i]);
+		}
+	}
+
+
+	void TestFloats(void)
+	{
+		printf("Testing floats...\n");
+		cFastRandom rnd;
+		float sum = 0;
+		const int BUCKETS = 8;
+		int Counts[BUCKETS];
+		memset(Counts, 0, sizeof(Counts));
+		const int ITER = 10000;
+		for (int i = 0; i < ITER; i++)
+		{
+			float v = rnd.NextFloat(1000);
+			ASSERT(v >= 0);
+			ASSERT(v <= 1000);
+			Counts[((int)v) % BUCKETS]++;
+			sum += v;
+		}
+		sum = sum / ITER;
+		printf("avg: %f\n", sum);
+		for (int i = 0; i < BUCKETS; i++)
+		{
+			printf("  bucket %d: %d\n", i, Counts[i]);
+		}
+	}
+} g_Test;
+
+#endif
+
+
+
+
+
+
+int cFastRandom::m_SeedCounter = 0;
+
+
+
+
+
+cFastRandom::cFastRandom(void) :
+	m_Seed(m_SeedCounter++)
+{
+}
+
+
+
+
+
+int cFastRandom::NextInt(int a_Range)
+{
+	ASSERT(a_Range <= 1000000);  // The random is not sufficiently linearly distributed with bigger ranges
+	ASSERT(a_Range > 0);
+	
+	// Make the m_Counter operations as minimal as possible, to emulate atomicity
+	int Counter = m_Counter++;
+	
+	// Use a_Range, m_Counter and m_Seed as inputs to the pseudorandom function:
+	int n = a_Range + m_Counter * 57 + m_Seed * 57 * 57;
+	n = (n << 13) ^ n;
+	n = ((n * (n * n * 15731 + 789221) + 1376312589) & 0x7fffffff);
+	return ((n / 11) % a_Range);
+}
+
+
+
+
+
+int cFastRandom::NextInt(int a_Range, int a_Salt)
+{
+	ASSERT(a_Range <= 1000000);  // The random is not sufficiently linearly distributed with bigger ranges
+	ASSERT(a_Range > 0);
+	
+	// Make the m_Counter operations as minimal as possible, to emulate atomicity
+	int Counter = m_Counter++;
+	
+	// Use a_Range, a_Salt, m_Counter and m_Seed as inputs to the pseudorandom function:
+	int n = a_Range + m_Counter * 57 + m_Seed * 57 * 57 + a_Salt * 57 * 57 * 57;
+	n = (n << 13) ^ n;
+	n = ((n * (n * n * 15731 + 789221) + 1376312589) & 0x7fffffff);
+	return ((n / 11) % a_Range);
+}
+
+
+
+
+
+float cFastRandom::NextFloat(float a_Range)
+{
+	// Make the m_Counter operations as minimal as possible, to emulate atomicity
+	int Counter = m_Counter++;
+	
+	// Use a_Range, a_Salt, m_Counter and m_Seed as inputs to the pseudorandom function:
+	int n = (int)a_Range + m_Counter * 57 + m_Seed * 57 * 57;
+	n = (n << 13) ^ n;
+	n = ((n * (n * n * 15731 + 789221) + 1376312589) & 0x7fffffff);
+	
+	// Convert the integer into float with the specified range:
+	return (((float)n / (float)0x7fffffff) * a_Range);
+}
+
+
+
+
+
+float cFastRandom::NextFloat(float a_Range, int a_Salt)
+{
+	// Make the m_Counter operations as minimal as possible, to emulate atomicity
+	int Counter = m_Counter++;
+	
+	// Use a_Range, a_Salt, m_Counter and m_Seed as inputs to the pseudorandom function:
+	int n = (int)a_Range + m_Counter * 57 + m_Seed * 57 * 57 + a_Salt * 57 * 57 * 57;
+	n = (n << 13) ^ n;
+	n = ((n * (n * n * 15731 + 789221) + 1376312589) & 0x7fffffff);
+	
+	// Convert the integer into float with the specified range:
+	return (((float)n / (float)0x7fffffff) * a_Range);
+}
+
+
+
+

source/FastRandom.h

@@ -0,0 +1,57 @@
+
+// FastRandom.h
+
+// Declares the cFastRandom class representing a fast random number generator
+
+/*
+The cFastRandom aims to provide a very fast, although not very cryptographically secure, random generator.
+It is fast to instantiate, fast to query next, and partially multi-thread-safe.
+It is multi-thread-safe in the sense that it can be accessed from multiple threads without crashing, but it may
+yield duplicate numbers in that case.
+
+Internally, this works similar to cNoise's integral noise generation, with some predefined inputs: the seed is
+taken from a global counter and the random is calculated using a counter that is incremented on each use (hence
+the multi-thread duplication). Two alternatives exists for each function, one that takes a range parameter,
+and another that takes an additional "salt" parameter; this salt is used as an additional input to the random,
+in order to avoid multi-thread duplication. If two threads both use the class at the same time with different
+salts, the values they get will be different.
+*/
+
+
+
+
+
+#pragma once
+
+
+
+
+
+class cFastRandom
+{
+public:
+	cFastRandom(void);
+	
+	/// Returns a random int in the range [0 .. a_Range - 1]; a_Range must be less than 1M
+	int NextInt(int a_Range);
+
+	/// Returns a random int in the range [0 .. a_Range - 1]; a_Range must be less than 1M; a_Salt is additional source of randomness
+	int NextInt(int a_Range, int a_Salt);
+	
+	/// Returns a random float in the range [0 .. a_Range]; a_Range must be less than 1M
+	float NextFloat(float a_Range);
+
+	/// Returns a random float in the range [0 .. a_Range]; a_Range must be less than 1M; a_Salt is additional source of randomness
+	float NextFloat(float a_Range, int a_Salt);
+	
+protected:
+	int m_Seed;
+	int m_Counter;
+	
+	/// Counter that is used to initialize the seed, incremented for each object created
+	static int m_SeedCounter;
+} ;
+
+
+
+