﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace Voron.Graph
{
	public static class Util
	{
		//taken from here
		//http://jasonf-blog.blogspot.co.il/2006/08/hanselmans-endianess-converter.html
		private static readonly byte[] _flippedBytes = {
			0x00, 0x80, 0x40, 0xC0, 0x20, 0xA0, 0x60, 0xE0,
			0x10, 0x90, 0x50, 0xD0, 0x30, 0xB0, 0x70, 0xF0,
			0x08, 0x88, 0x48, 0xC8, 0x28, 0xA8, 0x68, 0xE8,
			0x18, 0x98, 0x58, 0xD8, 0x38, 0xB8, 0x78, 0xF8,
			0x04, 0x84, 0x44, 0xC4, 0x24, 0xA4, 0x64, 0xE4,
			0x14, 0x94, 0x54, 0xD4, 0x34, 0xB4, 0x74, 0xF4,
			0x0C, 0x8C, 0x4C, 0xCC, 0x2C, 0xAC, 0x6C, 0xEC,
			0x1C, 0x9C, 0x5C, 0xDC, 0x3C, 0xBC, 0x7C, 0xFC,
			0x02, 0x82, 0x42, 0xC2, 0x22, 0xA2, 0x62, 0xE2,
			0x12, 0x92, 0x52, 0xD2, 0x32, 0xB2, 0x72, 0xF2,
			0x0A, 0x8A, 0x4A, 0xCA, 0x2A, 0xAA, 0x6A, 0xEA,
			0x1A, 0x9A, 0x5A, 0xDA, 0x3A, 0xBA, 0x7A, 0xFA,
			0x06, 0x86, 0x46, 0xC6, 0x26, 0xA6, 0x66, 0xE6,
			0x16, 0x96, 0x56, 0xD6, 0x36, 0xB6, 0x76, 0xF6,
			0x0E, 0x8E, 0x4E, 0xCE, 0x2E, 0xAE, 0x6E, 0xEE,
			0x1E, 0x9E, 0x5E, 0xDE, 0x3E, 0xBE, 0x7E, 0xFE,
			0x01, 0x81, 0x41, 0xC1, 0x21, 0xA1, 0x61, 0xE1,
			0x11, 0x91, 0x51, 0xD1, 0x31, 0xB1, 0x71, 0xF1,
			0x09, 0x89, 0x49, 0xC9, 0x29, 0xA9, 0x69, 0xE9,
			0x19, 0x99, 0x59, 0xD9, 0x39, 0xB9, 0x79, 0xF9,
			0x05, 0x85, 0x45, 0xC5, 0x25, 0xA5, 0x65, 0xE5,
			0x15, 0x95, 0x55, 0xD5, 0x35, 0xB5, 0x75, 0xF5,
			0x0D, 0x8D, 0x4D, 0xCD, 0x2D, 0xAD, 0x6D, 0xED,
			0x1D, 0x9D, 0x5D, 0xDD, 0x3D, 0xBD, 0x7D, 0xFD,
			0x03, 0x83, 0x43, 0xC3, 0x23, 0xA3, 0x63, 0xE3,
			0x13, 0x93, 0x53, 0xD3, 0x33, 0xB3, 0x73, 0xF3,
			0x0B, 0x8B, 0x4B, 0xCB, 0x2B, 0xAB, 0x6B, 0xEB,
			0x1B, 0x9B, 0x5B, 0xDB, 0x3B, 0xBB, 0x7B, 0xFB,
			0x07, 0x87, 0x47, 0xC7, 0x27, 0xA7, 0x67, 0xE7,
			0x17, 0x97, 0x57, 0xD7, 0x37, 0xB7, 0x77, 0xF7,
			0x0F, 0x8F, 0x4F, 0xCF, 0x2F, 0xAF, 0x6F, 0xEF,
			0x1F, 0x9F, 0x5F, 0xDF, 0x3F, 0xBF, 0x7F, 0xFF
		};

		private static readonly ushort[] _flippedWords = new ushort[1 << 16];

		static Util()
		{
			for (int i = 0; i < _flippedWords.Length; i++)
			{
				_flippedWords[i] = (ushort)((_flippedBytes[i & 0xff] << 8)
										   | _flippedBytes[(i >> 8)]);
			}
		}

		public static long ReverseBits(long num)
		{
			long z = 0;
			const int bits = sizeof(long) * 8;
			z = (z << 16) | _flippedWords[num & 0xffff];
			num = num >> 16;
			z = (z << 16) | _flippedWords[num & 0xffff];
			num = num >> 16;
			z = (z << 16) | _flippedWords[num & 0xffff];
			num = num >> 16;
			z = (z << 16) | _flippedWords[num & 0xffff];
			num = num >> 16;

			return z >> (64 - bits);
		}
	}
}
