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using System;
namespace NLangDetect.Core.Extensions
{
public static class RandomExtensions
{
private const double _Epsilon = 2.22044604925031E-15;
private static readonly object _mutex = new object();
private static double _nextNextGaussian;
private static bool _hasNextNextGaussian;
/// <summary>
/// Returns the next pseudorandom, Gaussian ("normally") distributed double value with mean 0.0 and standard deviation 1.0 from this random number generator's sequence.
/// The general contract of nextGaussian is that one double value, chosen from (approximately) the usual normal distribution with mean 0.0 and standard deviation 1.0, is pseudorandomly generated and returned.
/// </summary>
/// <remarks>
/// Taken from: http://download.oracle.com/javase/6/docs/api/java/util/Random.html (nextGaussian())
/// </remarks>
public static double NextGaussian(this Random random)
{
lock (_mutex)
{
if (_hasNextNextGaussian)
{
_hasNextNextGaussian = false;
return _nextNextGaussian;
}
double v1, v2, s;
do
{
v1 = 2.0 * random.NextDouble() - 1.0; // between -1.0 and 1.0
v2 = 2.0 * random.NextDouble() - 1.0; // between -1.0 and 1.0
s = v1 * v1 + v2 * v2;
}
while (s >= 1.0 || Math.Abs(s - 0.0) < _Epsilon);
double multiplier = Math.Sqrt(-2.0 * Math.Log(s) / s);
_nextNextGaussian = v2 * multiplier;
_hasNextNextGaussian = true;
return v1 * multiplier;
}
}
}
}
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