Utils.cs

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#region License
/*This file is part of Satsuma Graph Library
Copyright © 2013 Balázs Szalkai

This software is provided 'as-is', without any express or implied
warranty. In no event will the authors be held liable for any damages
arising from the use of this software.

Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute it
freely, subject to the following restrictions:

   1. The origin of this software must not be misrepresented; you must not
   claim that you wrote the original software. If you use this software
   in a product, an acknowledgment in the product documentation would be
   appreciated but is not required.

   2. Altered source versions must be plainly marked as such, and must not be
   misrepresented as being the original software.

   3. This notice may not be removed or altered from any source
   distribution.*/
#endregion

using System;
using System.Collections.Generic;
using System.Linq;
using System.Xml.Linq;

namespace Satsuma
{
    public interface IClearable
    {
        void Clear();
    }

    internal static class Utils
    {
        public static double LargestPowerOfTwo(double d)
        {
            long bits = BitConverter.DoubleToInt64Bits(d);
            bits &= 0x7FF0000000000000; // clear mantissa
            if (bits == 0x7FF0000000000000) bits = 0x7FE0000000000000; // deal with infinity
            return BitConverter.Int64BitsToDouble(bits);
        }

        public static V MakeEntry<K, V>(Dictionary<K, V> dict, K key)
            where V : new()
        {
            V result;
            if (dict.TryGetValue(key, out result)) return result;
            return (dict[key] = new V());
        }

        public static void RemoveAll<T>(List<T> list, Func<T, bool> condition)
        {
            for (int i = 0; i < list.Count; ++i)
            {
                if (condition(list[i]))
                {
                    if (i < list.Count - 1)
                        list[i] = list[list.Count - 1];
                    list.RemoveAt(list.Count - 1);
                }
            }
        }

        public static void RemoveAll<T>(HashSet<T> set, Func<T, bool> condition)
        {
            foreach (var x in set.Where(condition).ToList())
                set.Remove(x);
        }

        public static void RemoveAll<K, V>(Dictionary<K, V> dict, Func<K, bool> condition)
        {
            foreach (var key in dict.Keys.Where(condition).ToList())
                dict.Remove(key);
        }

        public static void RemoveLast<T>(List<T> list, T element)
            where T : IEquatable<T>
        {
            for (int i = list.Count - 1; i >= 0; i--)
            {
                if (element.Equals(list[i]))
                {
                    list.RemoveAt(i);
                    break;
                }
            }
        }

        public static IEnumerable<XElement> ElementsLocal(XElement xParent, string localName)
        {
            return xParent.Elements().Where(x => x.Name.LocalName == localName);
        }

        public static XElement ElementLocal(XElement xParent, string localName)
        {
            return ElementsLocal(xParent, localName).FirstOrDefault();
        }
    }

    internal abstract class IdAllocator
    {
        private long randomSeed;
        private long lastAllocated;

        public IdAllocator()
        {
            randomSeed = 205891132094649; // 3^30
            Rewind();
        }

        private long Random()
        {
            return (randomSeed *= 3);
        }

        protected abstract bool IsAllocated(long id);

        public void Rewind()
        {
            lastAllocated = 0;
        }

        public long Allocate()
        {
            long id = lastAllocated+1;
            int streak = 0;
            while (true)
            {
                if (id == 0) id = 1;
                if (!IsAllocated(id))
                {
                    lastAllocated = id;
                    return id;
                }

                id++;
                streak++;
                if (streak >= 100)
                {
                    id = Random();
                    streak = 0;
                }
            }
        }
    }
}