Project-Reboot-3.0/Project Reboot 3.0/UnrealMathUtility.h

#pragma once

#include "GenericPlatformMath.h"

struct FMath : public FGenericPlatformMath
{
	template< class T >
	static FORCEINLINE T Clamp(const T X, const T Min, const T Max)
	{
		return X < Min ? Min : X < Max ? X : Max;
	}

	template< class T >
	static FORCEINLINE T Square(const T A)
	{
		return A * A;
	}

	static float SRand() // T(REP)
	{
		return rand();
	}

	static FORCEINLINE uint32 FloorLog2(uint32 Value)
	{
		/*		// reference implementation
				// 1500ms on test data
				uint32 Bit = 32;
				for (; Bit > 0;)
				{
					Bit--;
					if (Value & (1<<Bit))
					{
						break;
					}
				}
				return Bit;
		*/
		// same output as reference

		// see http://codinggorilla.domemtech.com/?p=81 or http://en.wikipedia.org/wiki/Binary_logarithm but modified to return 0 for a input value of 0
		// 686ms on test data
		uint32 pos = 0;
		if (Value >= 1 << 16) { Value >>= 16; pos += 16; }
		if (Value >= 1 << 8) { Value >>= 8; pos += 8; }
		if (Value >= 1 << 4) { Value >>= 4; pos += 4; }
		if (Value >= 1 << 2) { Value >>= 2; pos += 2; }
		if (Value >= 1 << 1) { pos += 1; }
		return (Value == 0) ? 0 : pos;

		// even faster would be method3 but it can introduce more cache misses and it would need to store the table somewhere
		// 304ms in test data
		/*int LogTable256[256];

		void prep()
		{
			LogTable256[0] = LogTable256[1] = 0;
			for (int i = 2; i < 256; i++)
			{
				LogTable256[i] = 1 + LogTable256[i / 2];
			}
			LogTable256[0] = -1; // if you want log(0) to return -1
		}

		int _forceinline method3(uint32 v)
		{
			int r;     // r will be lg(v)
			uint32 tt; // temporaries

			if ((tt = v >> 24) != 0)
			{
				r = (24 + LogTable256[tt]);
			}
			else if ((tt = v >> 16) != 0)
			{
				r = (16 + LogTable256[tt]);
			}
			else if ((tt = v >> 8 ) != 0)
			{
				r = (8 + LogTable256[tt]);
			}
			else
			{
				r = LogTable256[v];
			}
			return r;
		}*/
	}

	static FORCEINLINE uint32 CountLeadingZeros(uint32 Value)
	{
		if (Value == 0) return 32;
		return 31 - FloorLog2(Value);
	}

	template <class T>
	static constexpr FORCEINLINE T DivideAndRoundUp(T Dividend, T Divisor)
	{
		return (Dividend + Divisor - 1) / Divisor;
	}

	static FORCEINLINE int32 Rand() { return rand(); }

	static FORCEINLINE float FRand() { return Rand() / (float)RAND_MAX; }

#define FASTASIN_HALF_PI (1.5707963050f)
	/**
	* Computes the ASin of a scalar value.
	*
	* @param Value  input angle
	* @return ASin of Value
	*/
	static FORCEINLINE float FastAsin(float Value)
	{
		// Clamp input to [-1,1].
		bool nonnegative = (Value >= 0.0f);
		float x = FMath::Abs(Value);
		float omx = 1.0f - x;
		if (omx < 0.0f)
		{
			omx = 0.0f;
		}
		float root = FMath::Sqrt(omx);
		// 7-degree minimax approximation
		float result = ((((((-0.0012624911f * x + 0.0066700901f) * x - 0.0170881256f) * x + 0.0308918810f) * x - 0.0501743046f) * x + 0.0889789874f) * x - 0.2145988016f) * x + FASTASIN_HALF_PI;
		result *= root;  // acos(|x|)
		// acos(x) = pi - acos(-x) when x < 0, asin(x) = pi/2 - acos(x)
		return (nonnegative ? FASTASIN_HALF_PI - result : result - FASTASIN_HALF_PI);
	}
#undef FASTASIN_HALF_PI
};