RandomStream.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "uLang/Common/Common.h"
#include <cstring> // for memcpy().
 
namespace uLang
{
 
class CRandomStream
{
public:
 
    CRandomStream(int32_t Seed = 0)
        : _Seed(Seed)
    {}
 
    void Initialize(int32_t Seed)
    {
        _Seed = uint32_t(Seed);
    }
 
    int32_t RandRange(int32_t Min, int32_t Max)
    {
        MutateSeed();
 
        const int64_t Range = int64_t(Max) - int64_t(Min) + 1;
        return Min + uint32_t(Range == 0 ? 0 : (int64_t(_Seed) % Range));
    }
    
    float FRandRange(float Min, float Max)
    {
        MutateSeed();
 
        uint32_t UnitFractionAsInt = 0x3F800000U | (_Seed >> 9);
        float UnitFraction;
        memcpy(&UnitFraction, &UnitFractionAsInt, sizeof(float));
 
        return Min + (UnitFraction - 1.0f) * (Max - Min);
    }
 
    bool RandBool()
    {
        MutateSeed();
        return !!(_Seed & 1);
    }
 
protected:
 
    void MutateSeed()
    {
        _Seed = (_Seed * 196314165U) + 907633515U; 
    }
 
private:
 
    // Holds the current seed. This should be an uint32 so that any shift to obtain top bits
    // is a logical shift, rather than an arithmetic shift (which smears down the negative bit).
    uint32_t _Seed;
};
 
}