/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/.
 */

#pragma once

#ifndef __is_identifier
#define __is_identifier(x) 1  // Compatibility with non-clang compilers.
#endif

#define __has_keyword(__x) !(__is_identifier(__x))

// map a half float type, if available, to float16
#if __has_keyword(_Float16)
	typedef _Float16    float16;
#elif __has_keyword(__fp16)
	typedef __fp16      float16;
#else

class float16
{
	uint16_t m_data;

	union IEEE_FP16
	{
		uint16_t data;
		struct
		{
			uint16_t mantissa : 10;
			uint16_t exponent : 5;
			uint16_t sign     : 1;
		} IEEE;
	};

	// Helper for conversion
	union IEEE_FP32
	{
		float Float;
		struct
		{
			uint32_t mantissa : 23;
			uint32_t exponent : 8;
			uint32_t sign     : 1;
		} IEEE;
	};

	static constexpr uint16_t float2half(float value)
	{
		IEEE_FP32 f;
		f.Float = value;

		IEEE_FP16 fp16;
		fp16.IEEE.sign = f.IEEE.sign;

		if ( !f.IEEE.exponent)
		{
			fp16.IEEE.mantissa = 0;
			fp16.IEEE.exponent = 0;
		}
		else if (f.IEEE.exponent==0xff)
		{
			// NaN or INF
			fp16.IEEE.mantissa = (f.IEEE.mantissa!=0) ? 1 : 0;
			fp16.IEEE.exponent = 31;
		}
		else
		{
			// regular number
			int new_exp = f.IEEE.exponent-127;

			if (new_exp<-24)
			{ // this maps to 0
				fp16.IEEE.mantissa = 0;
				fp16.IEEE.exponent = 0;
			}

			else if (new_exp < -14)
			{
				// this maps to a denorm
				fp16.IEEE.exponent = 0;
				unsigned int exp_val = (unsigned int) (-14 - new_exp);  // 2^-exp_val
				switch (exp_val)
				{
					case 0:
						fp16.IEEE.mantissa = 0;
						break;
					case 1: fp16.IEEE.mantissa = 512 + (f.IEEE.mantissa>>14); break;
					case 2: fp16.IEEE.mantissa = 256 + (f.IEEE.mantissa>>15); break;
					case 3: fp16.IEEE.mantissa = 128 + (f.IEEE.mantissa>>16); break;
					case 4: fp16.IEEE.mantissa = 64 + (f.IEEE.mantissa>>17); break;
					case 5: fp16.IEEE.mantissa = 32 + (f.IEEE.mantissa>>18); break;
					case 6: fp16.IEEE.mantissa = 16 + (f.IEEE.mantissa>>19); break;
					case 7: fp16.IEEE.mantissa = 8 + (f.IEEE.mantissa>>20); break;
					case 8: fp16.IEEE.mantissa = 4 + (f.IEEE.mantissa>>21); break;
					case 9: fp16.IEEE.mantissa = 2 + (f.IEEE.mantissa>>22); break;
					case 10: fp16.IEEE.mantissa = 1; break;
				}
			}
			else if (new_exp>15)
			{ // map this value to infinity
				fp16.IEEE.mantissa = 0;
				fp16.IEEE.exponent = 31;
			}
			else
			{
				fp16.IEEE.exponent = new_exp+15;
				fp16.IEEE.mantissa = (f.IEEE.mantissa >> 13);
			}
		}
		return fp16.data;
	}

public:
	constexpr float16() : m_data(0) {}

	constexpr float16(const float16&) = default;

	constexpr float16(float16&&) = default;

	template<typename T, std::enable_if_t<std::is_convertible_v<T, float>, bool> = true>
	constexpr float16(const T& other) : m_data(float2half(static_cast<float>(other))) {}

	constexpr float16(uint16_t mantissa, uint16_t exponent, uint16_t sign)
	{
		IEEE_FP16 fp16;
		fp16.IEEE.mantissa = mantissa;
		fp16.IEEE.exponent = exponent;
		fp16.IEEE.sign = sign;
		m_data = fp16.data;
	}

	//region operators
	// Operator +=, -=, *=, /= and +, -, *, /
	#define BINARY_ARITHMETIC_OPERATOR(OP)                                                     \
		template<typename T, std::enable_if_t<std::is_convertible_v<T, float>, bool> = true>   \
		constexpr float16& operator OP##=(const T& rhs) {                                                \
			return *this = operator float() OP static_cast<float>(rhs);                        \
		}                                                                                      \
		template<typename T, std::enable_if_t<std::is_convertible_v<T, float>, bool> = true>   \
		[[nodiscard]] constexpr float16 operator OP(const T& rhs) const {                                      \
			return { operator float() OP static_cast<T>(rhs) };                               \
		}

	BINARY_ARITHMETIC_OPERATOR(+)
	BINARY_ARITHMETIC_OPERATOR(-)
	BINARY_ARITHMETIC_OPERATOR(*)
	BINARY_ARITHMETIC_OPERATOR(/)

	#undef BINARY_ARITHMETIC_OPERATOR

	// Operator ++, --
	constexpr float16& operator++()
	{
		return *this += 1;
	}

	constexpr float16 operator++(int)
	{
		float16 ret(*this);
		operator++();
		return ret;
	}

	constexpr float16& operator--()
	{
		return *this -= 1;
	}

	constexpr float16 operator--(int)
	{
		float16 ret(*this);
		operator--();
		return ret;
	}

	template<typename T, std::enable_if_t<std::is_convertible_v<T, float>, bool> = true>
	constexpr float16& operator=(const T& rhs)
	{
		m_data = float2half(rhs);
		return *this;
	}

	template<typename T, std::enable_if_t<std::is_convertible_v<T, float>, bool> = true>
	[[nodiscard]] constexpr auto operator<=>(const T& other) const { return operator float() <=> static_cast<float>(other); }
	//endregion

	// Operator float
	[[nodiscard]] constexpr operator float() const
	{
		IEEE_FP32 fp32;
		IEEE_FP16 fp16;
		fp16.data = m_data;
		fp32.IEEE.sign = fp16.IEEE.sign;

		if (!fp16.IEEE.exponent)
		{
			if (!fp16.IEEE.mantissa)
			{
				fp32.IEEE.mantissa = 0;
				fp32.IEEE.exponent = 0;
			}
			else
			{
				const float half_denorm = 1.0f / 16384.0f;
				float mantissa = static_cast<float>(fp16.IEEE.mantissa) / 1024.0f;
				float sgn = (fp16.IEEE.sign) ? -1.0f : 1.0f;
				fp32.Float = sgn * mantissa * half_denorm;
			}
		}
		else if (31 == fp16.IEEE.exponent)
		{
			fp32.IEEE.exponent = 0xff;
			fp32.IEEE.mantissa = (fp16.IEEE.mantissa != 0) ? 1 : 0;
		}
		else
		{
			fp32.IEEE.exponent = fp16.IEEE.exponent + 112;
			fp32.IEEE.mantissa = fp16.IEEE.mantissa << 13;
		}
		return fp32.Float;
	}

	template<typename Key> friend
	struct std::hash;
};

namespace std
{
	template<>
	struct hash<float16>
	{
		std::size_t operator()(const float16& key) const
		{
			return hash<uint16_t>()(key.m_data);
		}
	};

	template <>
	class numeric_limits<float16>
	{
	public:
		// General -- meaningful for all specializations.
		static const bool is_specialized = true;
		static float16 min() { return float16(0, 1, 0); }
		static float16 max() { return float16(~0, 30, 0); }
		static const int radix = 2;
		static const int digits = 10;   // conservative assumption
		static const int digits10 = 2;  // conservative assumption
		static const bool is_signed		= true;
		static const bool is_integer	= true;
		static const bool is_exact		= false;
		static const bool traps			= false;
		static const bool is_modulo		= false;
		static const bool is_bounded	= true;

		// Floating point specific.

		static float16 epsilon() { return float16(0.00097656f); } // from OpenEXR, needs to be confirmed
		static float16 round_error() { return float16(0.00097656f/2); }
		static const int min_exponent10 = -9;
		static const int max_exponent10 = 9;
		static const int min_exponent   = -15;
		static const int max_exponent   = 15;

		static const bool has_infinity			= true;
		static const bool has_quiet_NaN			= true;
		static const bool has_signaling_NaN		= true;
		static const bool is_iec559				= false;
		static const bool has_denorm			= denorm_present;
		static const bool tinyness_before		= false;
		static const float_round_style round_style = round_to_nearest;

		static float16 denorm_min() { return float16(1, 0, 1); }
		static float16 infinity() { return float16(0, 31, 0); }
		static float16 quiet_NaN() { return float16(1, 31, 0); }
		static float16 signaling_NaN () { return float16(1, 31, 0); }
	};
}

#endif
#undef __has_keyword


typedef float16 fp16;
typedef float16 half;