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Source/Engine/Core/RandomStream.h

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+// Copyright (c) 2012-2020 Wojciech Figat. All rights reserved.
+
+#pragma once
+
+#include "Types/BaseTypes.h"
+#include "Math/Vector3.h"
+#include "Math/Math.h"
+#include <stdlib.h>
+
+/// <summary>
+/// Very basic pseudo numbers generator.
+/// </summary>
+class RandomStream
+{
+private:
+
+    /// <summary>
+    /// Holds the initial seed.
+    /// </summary>
+    int32 _initialSeed;
+
+    /// <summary>
+    /// Holds the current seed.
+    /// </summary>
+    mutable int32 _seed;
+
+public:
+
+    /// <summary>
+    /// Init
+    /// </summary>
+    RandomStream()
+        : _initialSeed(0)
+        , _seed(0)
+    {
+    }
+
+    /// <summary>
+    /// Creates and initializes a new random stream from the specified seed value.
+    /// </summary>
+    /// <param name="seed">The seed value.</param>
+    RandomStream(int32 seed)
+        : _initialSeed(seed)
+        , _seed(seed)
+    {
+    }
+
+public:
+
+    /// <summary>
+    /// Gets initial seed value
+    /// </summary>
+    /// <returns>Initial seed.</returns>
+    int32 GetInitialSeed() const
+    {
+        return _initialSeed;
+    }
+
+public:
+
+    /// <summary>
+    /// Gets the current seed.
+    /// </summary>
+    /// <returns>Current seed value.</returns>
+    int32 GetCurrentSeed() const
+    {
+        return _seed;
+    }
+
+    /// <summary>
+    /// Initializes this random stream with the specified seed value.
+    /// </summary>
+    /// <param name="seed">The seed value.</param>
+    void Initialize(int32 seed)
+    {
+        _initialSeed = seed;
+        _seed = seed;
+    }
+
+    /// <summary>
+    /// Resets this random stream to the initial seed value.
+    /// </summary>
+    void Reset() const
+    {
+        _seed = _initialSeed;
+    }
+
+    /// <summary>
+    /// Generates a new random seed.
+    /// </summary>
+    void GenerateNewSeed()
+    {
+        Initialize(rand());
+    }
+
+public:
+
+    /// <summary>
+    /// Returns a random number between 0 and MAXUINT.
+    /// </summary>
+    /// <returns>Random number.</returns>
+    uint32 GetUnsignedInt() const
+    {
+        MutateSeed();
+
+        return *(uint32*)&_seed;
+    }
+
+    /// <summary>
+    /// Returns a random number between 0 and 1.
+    /// </summary>
+    /// <returns>Random number.</returns>
+    float GetFraction() const
+    {
+        MutateSeed();
+        const float temp = 1.0f;
+        float result;
+        *(int32*)&result = (*(int32*)&temp & 0xff800000) | (_seed & 0x007fffff);
+        return Math::Fractional(result);
+    }
+
+    /// <summary>
+    /// Returns a random number between 0 and 1.
+    /// </summary>
+    /// <returns>Random number.</returns>
+    FORCE_INLINE float Rand() const
+    {
+        return GetFraction();
+    }
+
+    /// <summary>
+    /// Returns a random vector of unit size.
+    /// </summary>
+    /// <returns>Random unit length vector</returns>
+    Vector3 GetUnitVector() const
+    {
+        Vector3 result;
+        float l;
+        do
+        {
+            result.X = GetFraction() * 2.f - 1.f;
+            result.Y = GetFraction() * 2.f - 1.f;
+            result.Z = GetFraction() * 2.f - 1.f;
+            l = result.LengthSquared();
+        } while (l > 1.0f || l < ZeroTolerance);
+        return Vector3::Normalize(result);
+    }
+
+    /// <summary>
+    /// Helper function for rand implementations.
+    /// </summary>
+    /// <param name="A">Top border</param>
+    /// <returns>A random number in [0..A)</returns>
+    FORCE_INLINE int32 RandHelper(int32 A) const
+    {
+        return A > 0 ? Math::TruncToInt(GetFraction() * ((float)A - ZeroTolerance)) : 0;
+    }
+
+    /// <summary>
+    /// Helper function for rand implementations
+    /// </summary>
+    /// <param name="min">Minimum value</param>
+    /// <param name="max">Maximum value</param>
+    /// <returns>A random number in [min; max] range</returns>
+    FORCE_INLINE int32 RandRange(int32 min, int32 max) const
+    {
+        const int32 range = max - min + 1;
+        return min + RandHelper(range);
+    }
+
+    /// <summary>
+    /// Helper function for rand implementations
+    /// </summary>
+    /// <param name="min">Minimum value</param>
+    /// <param name="max">Maximum value</param>
+    /// <returns>A random number in [min; max] range</returns>
+    FORCE_INLINE float RandRange(float min, float max) const
+    {
+        return min + (max - min) * Rand();
+    }
+
+protected:
+
+    /// <summary>
+    /// Mutates the current seed into the next seed.
+    /// </summary>
+    void MutateSeed() const
+    {
+        // This can be modified to provide better randomization
+        _seed = _seed * 196314165 + 907633515;
+    }
+};