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Extensions.cs
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Extensions.cs
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using System;
using KeePassLib.Cryptography;
namespace KeePassDiceware
{
internal static class Extensions
{
/// <summary>
/// Generates a pseudorandom value in range [0, <paramref name="maxInclusive"/>] (both ends are inclusive).
/// </summary>
/// <param name="maxInclusive"> maximal value (inclusive) of random number.</param>
/// <returns>
/// Pseudorandom value from [0, <paramref name="maxInclusive"/>] range.
/// </returns>
public static ulong AtMost(this CryptoRandomStream random, ulong maxInclusive)
{
const ulong RANDOM_MAX = ulong.MaxValue; // GetRandomUInt64 max return value
if (maxInclusive == RANDOM_MAX)
{
return random.GetRandomUInt64();
}
ulong modulus = maxInclusive + 1;
ulong ceil = RANDOM_MAX - (RANDOM_MAX % modulus);
ulong generated;
do
{
generated = random.GetRandomUInt64();
} while (generated >= ceil);
return generated % modulus;
}
/// <summary>
/// Generates a pseudorandom value in range [0, <paramref name="maxInclusive"/>] (both ends are inclusive).
/// </summary>
/// <param name="maxInclusive"> maximal value (inclusive) of random number.</param>
/// <returns>
/// Pseudorandom value from [0, <paramref name="maxInclusive"/>] range.
/// </returns>
public static int AtMost(this CryptoRandomStream random, int maxInclusive)
{
if (maxInclusive < 0)
{
throw new ArgumentOutOfRangeException(nameof(maxInclusive), $"Must be positive");
}
ulong val = random.AtMost(Convert.ToUInt64(maxInclusive));
return checked((int)val); // maxInclusive <= int.MaxValue -> wont throw
}
/// <summary>
/// Generates a pseudorandom value in range [<paramref name="minInclusive"/>, <paramref name="maxInclusive"/>] (both ends are inclusive).
/// </summary>
/// <param name="minInclusive"> minimal value (inclusive) of random number.</param>
/// <param name="maxInclusive"> maximal value (inclusive) of random number.</param>
/// <returns>
/// Pseudorandom value from [<paramref name="minInclusive"/>, <paramref name="maxInclusive"/>] range.
/// </returns>
/// <exception cref="ArgumentOutOfRangeException">
/// Thrown when the <paramref name="minInclusive"/> is larger than <paramref name="maxInclusive"/>.
/// </exception>
public static int Range(this CryptoRandomStream random, int minInclusive, int maxInclusive)
{
if (minInclusive > maxInclusive)
{
throw new ArgumentOutOfRangeException(nameof(minInclusive), $"Must be smaller or equal to {nameof(maxInclusive)}");
}
int randomValue = AtMost(random, maxInclusive - minInclusive);
return randomValue + minInclusive;
}
/// <summary>
/// Selects a pseudorandom element from <paramref name="array"/>.
/// </summary>
/// <param name="array"> array from which to select the random element.</param>
/// <returns>
/// A pseudorandom element from <paramref name="array"/>.
/// </returns>
/// <exception cref="ArgumentException">
/// Thrown when <paramref name="array"/> is empty.
/// </exception>
public static T SelectRandom<T>(this T[] array, CryptoRandomStream random)
{
if (array.Length <= 0)
{
throw new ArgumentException(nameof(array), $"Unable to select a random member of empty object.");
}
int choice = random.AtMost(array.Length - 1);
return array[choice];
}
/// <summary>
/// Return TRUE with 50% probability. Simulates a perfect coin toss.
/// </summary>
/// <returns>
/// TRUE / FALSE with equal probabilities.
/// </returns>
public static bool CoinToss(this CryptoRandomStream random) => (random.GetRandomBytes(1)[0] & 1) == 0;
}
}