//
// Mono.Security.BitConverterLE.cs
//  Like System.BitConverter but always little endian
//
// Author:
//   Bernie Solomon
//

//
// 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.
//

using System;

namespace Mono.Security
{
	internal sealed class BitConverterLE
	{
		private BitConverterLE()
		{
		}

		unsafe private static byte[] GetUShortBytes(byte* bytes)
		{
			if (BitConverter.IsLittleEndian)
				return new byte[] { bytes[0], bytes[1] };
			else
				return new byte[] { bytes[1], bytes[0] };
		}

		unsafe private static byte[] GetUIntBytes(byte* bytes)
		{
			if (BitConverter.IsLittleEndian)
				return new byte[] { bytes[0], bytes[1], bytes[2], bytes[3] };
			else
				return new byte[] { bytes[3], bytes[2], bytes[1], bytes[0] };
		}

		unsafe private static byte[] GetULongBytes(byte* bytes)
		{
			if (BitConverter.IsLittleEndian)
				return new byte[] { bytes [0], bytes [1], bytes [2], bytes [3],
							 bytes [4], bytes [5], bytes [6], bytes [7] };
			else
				return new byte[] { bytes [7], bytes [6], bytes [5], bytes [4],
							 bytes [3], bytes [2], bytes [1], bytes [0] };
		}

		unsafe internal static byte[] GetBytes(bool value)
		{
			return new byte[] { value ? (byte)1 : (byte)0 };
		}

		unsafe internal static byte[] GetBytes(char value)
		{
			return GetUShortBytes((byte*)&value);
		}

		unsafe internal static byte[] GetBytes(short value)
		{
			return GetUShortBytes((byte*)&value);
		}

		unsafe internal static byte[] GetBytes(int value)
		{
			return GetUIntBytes((byte*)&value);
		}

		unsafe internal static byte[] GetBytes(long value)
		{
			return GetULongBytes((byte*)&value);
		}

		unsafe internal static byte[] GetBytes(ushort value)
		{
			return GetUShortBytes((byte*)&value);
		}

		unsafe internal static byte[] GetBytes(uint value)
		{
			return GetUIntBytes((byte*)&value);
		}

		unsafe internal static byte[] GetBytes(ulong value)
		{
			return GetULongBytes((byte*)&value);
		}

		unsafe internal static byte[] GetBytes(float value)
		{
			return GetUIntBytes((byte*)&value);
		}

		unsafe internal static byte[] GetBytes(double value)
		{
			return GetULongBytes((byte*)&value);
		}

		unsafe private static void UShortFromBytes(byte* dst, byte[] src, int startIndex)
		{
			if (BitConverter.IsLittleEndian)
			{
				dst[0] = src[startIndex];
				dst[1] = src[startIndex + 1];
			}
			else
			{
				dst[0] = src[startIndex + 1];
				dst[1] = src[startIndex];
			}
		}

		unsafe private static void UIntFromBytes(byte* dst, byte[] src, int startIndex)
		{
			if (BitConverter.IsLittleEndian)
			{
				dst[0] = src[startIndex];
				dst[1] = src[startIndex + 1];
				dst[2] = src[startIndex + 2];
				dst[3] = src[startIndex + 3];
			}
			else
			{
				dst[0] = src[startIndex + 3];
				dst[1] = src[startIndex + 2];
				dst[2] = src[startIndex + 1];
				dst[3] = src[startIndex];
			}
		}

		unsafe private static void ULongFromBytes(byte* dst, byte[] src, int startIndex)
		{
			if (BitConverter.IsLittleEndian)
			{
				for (int i = 0; i < 8; ++i)
					dst[i] = src[startIndex + i];
			}
			else
			{
				for (int i = 0; i < 8; ++i)
					dst[i] = src[startIndex + (7 - i)];
			}
		}

		unsafe internal static bool ToBoolean(byte[] value, int startIndex)
		{
			return value[startIndex] != 0;
		}

		unsafe internal static char ToChar(byte[] value, int startIndex)
		{
			char ret;

			UShortFromBytes((byte*)&ret, value, startIndex);

			return ret;
		}

		unsafe internal static short ToInt16(byte[] value, int startIndex)
		{
			short ret;

			UShortFromBytes((byte*)&ret, value, startIndex);

			return ret;
		}

		unsafe internal static int ToInt32(byte[] value, int startIndex)
		{
			int ret;

			UIntFromBytes((byte*)&ret, value, startIndex);

			return ret;
		}

		unsafe internal static long ToInt64(byte[] value, int startIndex)
		{
			long ret;

			ULongFromBytes((byte*)&ret, value, startIndex);

			return ret;
		}

		unsafe internal static ushort ToUInt16(byte[] value, int startIndex)
		{
			ushort ret;

			UShortFromBytes((byte*)&ret, value, startIndex);

			return ret;
		}

		unsafe internal static uint ToUInt32(byte[] value, int startIndex)
		{
			uint ret;

			UIntFromBytes((byte*)&ret, value, startIndex);

			return ret;
		}

		unsafe internal static ulong ToUInt64(byte[] value, int startIndex)
		{
			ulong ret;

			ULongFromBytes((byte*)&ret, value, startIndex);

			return ret;
		}

		unsafe internal static float ToSingle(byte[] value, int startIndex)
		{
			float ret;

			UIntFromBytes((byte*)&ret, value, startIndex);

			return ret;
		}

		unsafe internal static double ToDouble(byte[] value, int startIndex)
		{
			double ret;

			ULongFromBytes((byte*)&ret, value, startIndex);

			return ret;
		}
	}
}
