/* SPDX-License-Identifier: Apache-2.0
*
* The OpenSearch Contributors require contributions made to
* this file be licensed under the Apache-2.0 license or a
* compatible open source license.
*/
/*
* Modifications Copyright OpenSearch Contributors. See
* GitHub history for details.
*
*  Licensed to Elasticsearch B.V. under one or more contributor
*  license agreements. See the NOTICE file distributed with
*  this work for additional information regarding copyright
*  ownership. Elasticsearch B.V. licenses this file to you under
*  the Apache License, Version 2.0 (the "License"); you may
*  not use this file except in compliance with the License.
*  You may obtain a copy of the License at
*
* 	http://www.apache.org/licenses/LICENSE-2.0
*
*  Unless required by applicable law or agreed to in writing,
*  software distributed under the License is distributed on an
*  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
*  KIND, either express or implied.  See the License for the
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#region Utf8Json License https://github.com/neuecc/Utf8Json/blob/master/LICENSE
// MIT License
//
// Copyright (c) 2017 Yoshifumi Kawai
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
#endregion

using System;
using System.Runtime.InteropServices;

namespace OpenSearch.Net.Utf8Json.Internal.DoubleConversion
{
	using uint32_t = UInt32;

	[StructLayout(LayoutKind.Explicit, Pack = 1)]
	internal struct UnionDoubleULong
	{
		[FieldOffset(0)]
		public double d;
		[FieldOffset(0)]
		public ulong u64;
	}

	[StructLayout(LayoutKind.Explicit, Pack = 1)]
	internal struct UnionFloatUInt
	{
		[FieldOffset(0)]
		public float f;
		[FieldOffset(0)]
		public uint u32;
	}

	// https://github.com/google/double-conversion/blob/master/double-conversion/ieee.h

	internal struct Double
	{
		private const ulong KSignMask = (0x8000000000000000);
		private const ulong KExponentMask = (0x7FF0000000000000);
		private const ulong KSignificandMask = (0x000FFFFFFFFFFFFF);
		private const ulong KHiddenBit = (0x0010000000000000);
		private const int KPhysicalSignificandSize = 52;  // Excludes the hidden bit.
		private const int KSignificandSize = 53;

		private const int KExponentBias = 0x3FF + KPhysicalSignificandSize;
		private const int KDenormalExponent = -KExponentBias + 1;
		private const int KMaxExponent = 0x7FF - KExponentBias;
		private const ulong KInfinity = (0x7FF0000000000000);
		private const ulong KNaN = (0x7FF8000000000000);

		private readonly ulong _d64;

		public Double(double d) => _d64 = new UnionDoubleULong { d = d }.u64;

		public Double(DiyFp d) => _d64 = DiyFpToUint64(d);

		// The value encoded by this Double must be greater or equal to +0.0.
		// It must not be special (infinity, or NaN).
		public DiyFp AsDiyFp() => new DiyFp(Significand(), Exponent());

		// The value encoded by this Double must be strictly greater than 0.
		public DiyFp AsNormalizedDiyFp()
		{
			var f = Significand();
			var e = Exponent();

			// The current double could be a denormal.
			while ((f & KHiddenBit) == 0)
			{
				f <<= 1;
				e--;
			}
			// Do the final shifts in one go.
			f <<= DiyFp.KSignificandSize - KSignificandSize;
			e -= DiyFp.KSignificandSize - KSignificandSize;
			return new DiyFp(f, e);
		}

		// Returns the double's bit as uint64.
		public ulong AsUint64() => _d64;

		// Returns the next greater double. Returns +infinity on input +infinity.
		public double NextDouble()
		{
			if (_d64 == KInfinity) return new Double(KInfinity).value();
			if (Sign() < 0 && Significand() == 0)
			{
				// -0.0
				return 0.0;
			}
			if (Sign() < 0)
				return new Double(_d64 - 1).value();

			return new Double(_d64 + 1).value();
		}

		public double PreviousDouble()
		{
			if (_d64 == (KInfinity | KSignMask)) return -Infinity();
			if (Sign() < 0)
				return new Double(_d64 + 1).value();

			if (Significand() == 0) return -0.0;
			return new Double(_d64 - 1).value();
		}

		public int Exponent()
		{
			if (IsDenormal()) return KDenormalExponent;

			var d64 = AsUint64();
			var biased_e =
				(int)((d64 & KExponentMask) >> KPhysicalSignificandSize);
			return biased_e - KExponentBias;
		}

		public ulong Significand()
		{
			var d64 = AsUint64();
			var significand = d64 & KSignificandMask;
			if (!IsDenormal())
				return significand + KHiddenBit;

			return significand;
		}

		// Returns true if the double is a denormal.
		public bool IsDenormal()
		{
			var d64 = AsUint64();
			return (d64 & KExponentMask) == 0;
		}

		// We consider denormals not to be special.
		// Hence only Infinity and NaN are special.
		public bool IsSpecial()
		{
			var d64 = AsUint64();
			return (d64 & KExponentMask) == KExponentMask;
		}

		public bool IsNan()
		{
			var d64 = AsUint64();
			return ((d64 & KExponentMask) == KExponentMask) &&
				((d64 & KSignificandMask) != 0);
		}

		public bool IsInfinite()
		{
			var d64 = AsUint64();
			return ((d64 & KExponentMask) == KExponentMask) &&
				((d64 & KSignificandMask) == 0);
		}

		public int Sign()
		{
			var d64 = AsUint64();
			return (d64 & KSignMask) == 0 ? 1 : -1;
		}

		// Precondition: the value encoded by this Double must be greater or equal
		// than +0.0.
		public DiyFp UpperBoundary() => new DiyFp(Significand() * 2 + 1, Exponent() - 1);

		// Computes the two boundaries of this.
		// The bigger boundary (m_plus) is normalized. The lower boundary has the same
		// exponent as m_plus.
		// Precondition: the value encoded by this Double must be greater than 0.
		public void NormalizedBoundaries(out DiyFp out_m_minus, out DiyFp out_m_plus)
		{
			var v = AsDiyFp();
			var __ = new DiyFp((v.F << 1) + 1, v.E - 1);
			var m_plus = DiyFp.Normalize(ref __);

			DiyFp m_minus;
			if (LowerBoundaryIsCloser())
				m_minus = new DiyFp((v.F << 2) - 1, v.E - 2);
			else
				m_minus = new DiyFp((v.F << 1) - 1, v.E - 1);
			m_minus.F = m_minus.F << (m_minus.E - m_plus.E);
			m_minus.E = (m_plus.E);
			out_m_plus = m_plus;
			out_m_minus = m_minus;
		}

		public bool LowerBoundaryIsCloser()
		{
			// The boundary is closer if the significand is of the form f == 2^p-1 then
			// the lower boundary is closer.
			// Think of v = 1000e10 and v- = 9999e9.
			// Then the boundary (== (v - v-)/2) is not just at a distance of 1e9 but
			// at a distance of 1e8.
			// The only exception is for the smallest normal: the largest denormal is
			// at the same distance as its successor.
			// Note: denormals have the same exponent as the smallest normals.
			var physical_significand_is_zero = ((AsUint64() & KSignificandMask) == 0);
			return physical_significand_is_zero && (Exponent() != KDenormalExponent);
		}

		public double value() => new UnionDoubleULong { u64 = _d64 }.d;

		// Returns the significand size for a given order of magnitude.
		// If v = f*2^e with 2^p-1 <= f <= 2^p then p+e is v's order of magnitude.
		// This function returns the number of significant binary digits v will have
		// once it's encoded into a double. In almost all cases this is equal to
		// kSignificandSize. The only exceptions are denormals. They start with
		// leading zeroes and their effective significand-size is hence smaller.
		public static int SignificandSizeForOrderOfMagnitude(int order)
		{
			if (order >= (KDenormalExponent + KSignificandSize))
				return KSignificandSize;
			if (order <= KDenormalExponent)
				return 0;

			return order - KDenormalExponent;
		}

		public static double Infinity() => new Double(KInfinity).value();

		public static double NaN() => new Double(KNaN).value();

		public static ulong DiyFpToUint64(DiyFp diy_fp)
		{
			var significand = diy_fp.F;
			var exponent = diy_fp.E;
			while (significand > KHiddenBit + KSignificandMask)
			{
				significand >>= 1;
				exponent++;
			}
			if (exponent >= KMaxExponent)
				return KInfinity;

			if (exponent < KDenormalExponent)
				return 0;

			while (exponent > KDenormalExponent && (significand & KHiddenBit) == 0)
			{
				significand <<= 1;
				exponent--;
			}
			ulong biased_exponent;
			if (exponent == KDenormalExponent && (significand & KHiddenBit) == 0)
				biased_exponent = 0;
			else
				biased_exponent = (ulong)(exponent + KExponentBias);

			return (significand & KSignificandMask) |
				(biased_exponent << KPhysicalSignificandSize);
		}
	}

	internal struct Single
	{
		private const int KExponentBias = 0x7F + KPhysicalSignificandSize;
		private const int KDenormalExponent = -KExponentBias + 1;
		private const int KMaxExponent = 0xFF - KExponentBias;
		private const uint KInfinity = 0x7F800000;
		private const uint KNaN = 0x7FC00000;

		private const uint KSignMask = 0x80000000;
		private const uint KExponentMask = 0x7F800000;
		private const uint KSignificandMask = 0x007FFFFF;
		private const uint KHiddenBit = 0x00800000;
		private const int KPhysicalSignificandSize = 23;  // Excludes the hidden bit.
		public const int KSignificandSize = 24;

		private readonly uint _d32;

		public Single(float f) => _d32 = new UnionFloatUInt { f = f }.u32;

		// The value encoded by this Single must be greater or equal to +0.0.
		// It must not be special (infinity, or NaN).
		public DiyFp AsDiyFp() => new DiyFp(Significand(), Exponent());

		// Returns the single's bit as uint64.
		public uint AsUint32() => _d32;

		public int Exponent()
		{
			if (IsDenormal()) return KDenormalExponent;

			var d32 = AsUint32();
			var biased_e = (int)((d32 & KExponentMask) >> KPhysicalSignificandSize);
			return biased_e - KExponentBias;
		}

		public uint Significand()
		{
			var d32 = AsUint32();
			var significand = d32 & KSignificandMask;
			if (!IsDenormal())
				return significand + KHiddenBit;

			return significand;
		}

		// Returns true if the single is a denormal.
		public bool IsDenormal()
		{
			var d32 = AsUint32();
			return (d32 & KExponentMask) == 0;
		}

		// We consider denormals not to be special.
		// Hence only Infinity and NaN are special.
		public bool IsSpecial()
		{
			var d32 = AsUint32();
			return (d32 & KExponentMask) == KExponentMask;
		}

		public bool IsNan()
		{
			var d32 = AsUint32();
			return ((d32 & KExponentMask) == KExponentMask) &&
				((d32 & KSignificandMask) != 0);
		}

		public bool IsInfinite()
		{
			var d32 = AsUint32();
			return ((d32 & KExponentMask) == KExponentMask) &&
				((d32 & KSignificandMask) == 0);
		}

		public int Sign()
		{
			var d32 = AsUint32();
			return (d32 & KSignMask) == 0 ? 1 : -1;
		}

		// Computes the two boundaries of this.
		// The bigger boundary (m_plus) is normalized. The lower boundary has the same
		// exponent as m_plus.
		// Precondition: the value encoded by this Single must be greater than 0.
		public void NormalizedBoundaries(out DiyFp out_m_minus, out DiyFp out_m_plus)
		{
			var v = AsDiyFp();
			var __ = new DiyFp((v.F << 1) + 1, v.E - 1);
			var m_plus = DiyFp.Normalize(ref __);
			DiyFp m_minus;
			if (LowerBoundaryIsCloser())
				m_minus = new DiyFp((v.F << 2) - 1, v.E - 2);
			else
				m_minus = new DiyFp((v.F << 1) - 1, v.E - 1);

			m_minus.F = (m_minus.F << (m_minus.E - m_plus.E));
			m_minus.E = (m_plus.E);
			out_m_plus = m_plus;
			out_m_minus = m_minus;
		}

		// Precondition: the value encoded by this Single must be greater or equal
		// than +0.0.
		public DiyFp UpperBoundary() => new DiyFp(Significand() * 2 + 1, Exponent() - 1);

		public bool LowerBoundaryIsCloser()
		{
			// The boundary is closer if the significand is of the form f == 2^p-1 then
			// the lower boundary is closer.
			// Think of v = 1000e10 and v- = 9999e9.
			// Then the boundary (== (v - v-)/2) is not just at a distance of 1e9 but
			// at a distance of 1e8.
			// The only exception is for the smallest normal: the largest denormal is
			// at the same distance as its successor.
			// Note: denormals have the same exponent as the smallest normals.
			var physical_significand_is_zero = ((AsUint32() & KSignificandMask) == 0);
			return physical_significand_is_zero && (Exponent() != KDenormalExponent);
		}

		public float value() => new UnionFloatUInt { u32 = _d32 }.f;

		public static float Infinity() => new Single(KInfinity).value();

		public static float NaN() => new Single(KNaN).value();
	}
}