1 files changed, 81 insertions, 0 deletions
diff --git a/Runtime/Math/Random/rand.h b/Runtime/Math/Random/rand.h
new file mode 100644
index 0000000..1971ab4
--- /dev/null
+++ b/Runtime/Math/Random/rand.h
@@ -0,0 +1,81 @@
+#ifndef RAND_H
+#define RAND_H
+
+/*
+Some random generator timings:
+MacBook Pro w/ Core 2 Duo 2.4GHz. Times are for gcc 4.0.1 (OS X 10.6.2) / VS2008 SP1 (Win XP SP3),
+in milliseconds for this loop (4915200 calls):
+
+ for (int j = 0; j < 100; ++j)
+   for (int i = 0; i < 128*128*3; ++i)
+     data[i] = (rnd.get() & 0x3) << 6;
+
+                  gcc   vs2008    Size
+C's rand():       57.0  109.3 ms     1
+Mersenne Twister: 56.0   37.4 ms  2500
+Unity 2.x LCG:    11.1    9.2 ms     4
+Xorshift 128:     15.0   17.8 ms    16
+Xorshift 32:      20.6   10.7 ms     4
+WELL 512:         43.6   55.1 ms    68 
+*/
+
+
+// Xorshift 128 implementation
+// Xorshift paper: http://www.jstatsoft.org/v08/i14/paper
+// Wikipedia: http://en.wikipedia.org/wiki/Xorshift
+class Rand {
+public:
+	
+	Rand (UInt32 seed = 0)
+	{
+		SetSeed (seed);
+	}
+	
+	UInt32 Get ()
+	{
+		UInt32 t;
+		t = x ^ (x << 11);
+		x = y; y = z; z = w;
+		return w = (w ^ (w >> 19)) ^ (t ^ (t >> 8));
+	}
+
+	inline static float GetFloatFromInt (UInt32 value)
+	{
+		// take 23 bits of integer, and divide by 2^23-1
+		return float(value & 0x007FFFFF) * (1.0f / 8388607.0f);
+	}
+
+	inline static UInt8 GetByteFromInt (UInt32 value)
+	{
+		// take the most significant byte from the 23-bit value
+		return UInt8(value >> (23 - 8));
+	}
+	
+	// random number between 0.0 and 1.0
+	float GetFloat ()
+	{
+		return GetFloatFromInt (Get ());
+	}
+
+	// random number between -1.0 and 1.0
+	float GetSignedFloat ()
+	{
+	    return GetFloat() * 2.0f - 1.0f;
+	}
+
+	void SetSeed (UInt32 seed)
+	{
+		x = seed;
+		y = x * 1812433253U + 1;
+		z = y * 1812433253U + 1;
+		w = z * 1812433253U + 1;
+	}
+	
+	UInt32 GetSeed () const { return x; }
+	
+private:
+	UInt32 x, y, z, w;
+};
+
+
+#endif