RNGCryptoServiceProvider - Random Number Review

Question

While looking for best attempts at generating truly random numbers, I stumbled upon this code example.

Looking for opinions on this snippet.

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Answer 1

I felt like this could be a lot simpler and achieved in fewer lines of code so I'll throw my effort in - this will always return a positive number between 0 and 1:

public double Random()
{
    using var csp = new RNGCryptoServiceProvider();

    byte[] b = new byte[8];
    csp.GetBytes(b);
    var lng = BitConverter.ToInt64(b, 0);
    var dbl = (double)(lng < 0 ? ~lng : lng);

    // Convert to a random number between 0 and 1
    return dbl / long.MaxValue;
}

Instead of creating a new RNGCryptoServiceProvider each time, a simple static field would do fine.

To return a random positive integer between two numbers this works fine - though you need to check min is less than max, and that both are positive:

public long RandomInt64(long min = 0, long max = long.MaxValue)
{
    // Check arguments
    if (min >= max)
    {
        throw new ArgumentOutOfRangeException(nameof(min), min, "Minimium value must be less than the maximum value.");
    }

    if (min < 0)
    {
        throw new ArgumentException("Minimum value must be at least 0.", nameof(min));
    }

    // Get the range between the specified minimum and maximum values
    var range = max - min;

    // Now add a random amount of the range to the minimum value - it will never exceed maximum value
    var add = Math.Round(range * Random());
    return (long)(min + add);
}