RandomExtensionMethods.cs

using System;
using System.Collections.Generic;

namespace RPG.Util {
    public static class RandomExtensionMethods
    {
        /// <summary>
        /// Returns a random long from min (inclusive) to max (exclusive)
        /// </summary>
        /// <param name="random">The given random instance</param>
        /// <param name="min">The inclusive minimum bound</param>
        /// <param name="max">The exclusive maximum bound.  Must be greater or equal to min</param>
        public static long NextLong(this Random random, long min, long max)
        {
            if(max < min)
                throw new ArgumentOutOfRangeException("max", "max must be >= min!");

            //Working with ulong so that modulo works correctly with values > long.MaxValue
            ulong uRange = (ulong)(max - min);

            //Loop to prevent a modolo bias; see http://stackoverflow.com/a/10984975/238419
            //for more information.
            //In the worst case, the expected number of calls is 2 (though usually it's
            //much closer to 1, depending on min/max) so this loop doesn't really hurt performance at all.
            ulong ulongRand;
            do
            {
                byte[] buf = new byte[8];
                random.NextBytes(buf);
                ulongRand = (ulong)BitConverter.ToInt64(buf, 0);
            } while(ulongRand > ulong.MaxValue - ((ulong.MaxValue % uRange) + 1) % uRange);

            return (long)(ulongRand % uRange) + min;
        }

        /// <summary>
        /// Returns a random long from 0 (inclusive) to max (exclusive)
        /// </summary>
        /// <param name="random">The given random instance</param>
        /// <param name="max">The exclusive maximum bound.  Must be greater or equal to min</param>
        public static long NextLong(this Random random, long max)
        {
            return random.NextLong(0, max);
        }

        /// <summary>
        /// Returns a random long over all possible values of long (except long.MaxValue, similar to
        /// random.Next())
        /// </summary>
        /// <param name="random">The given random instance</param>
        public static long NextLong(this Random random)
        {
            return random.NextLong(long.MinValue, long.MaxValue);
        }

        // Return a random item from an array.
        public static T RandomElement<T>(this T[] items) {
            // Return a random item.
            return items[UnityEngine.Random.Range(0, items.Length)];
        }

        // Return a random item from a list.
        public static T RandomElement<T>(this List<T> items) {
            // Return a random item.
            return items[UnityEngine.Random.Range(0, items.Count)];
        }
    }
}