/// <summary>
/// LCG constructor.
/// <para>It is possible to define a randMax value less than or equal to m-1, as used by
/// Rand48Lcg. Setting m to 0 negates the modulus.</para>
/// </summary>
/// <param name="randMax">Maximum value returned by Next()</param>
/// <param name="a">Multiplier</param>
/// <param name="c">Increment</param>
/// <param name="m">Modulus</param>
public LcgRng(ulong randMax, ulong a, ulong c, ulong m)
: base(randMax)
{
if (m != 0 && m <= randMax)
{
throw new ArgumentException("randMax", "The RandMax value " + randMax +
"is invalid (not possible with modulus " + m + ").");
}
mult = a;
inc = c;
mod = m;
// Determine a bit mask to use instead of modulus, if possible.
// This yields as big performance improvement as the C# "%" operator
// does not appear optimized where the maximum result is a power of 2 value.
// Default where modulus is 0,
// which implicitly means 2^64.
modMask = UInt64.MaxValue;
if (mod != 0)
{
modMask = mod - 1;
// Number of bits needed by modulus
int mbits = CleromUtil.BitSize(modMask);
// If not equal, we can't use a mask.
if (modMask != UInt64.MaxValue >> (64 - mbits))
{
modMask = 0;
}
}
}
/// <summary>
/// Subclasses must supply 'randMax', the maximum possible value returned by the
/// implementation of the Next() method.
/// </summary>
/// <param name="randMax">Maximum value returned by Next()</param>
public Rng(ulong randMax)
{
if (randMax == 0)
{
throw new ArgumentException("randMax", "RandMax cannot be zero!");
}
// Set read-only values
nativeMax = randMax;
native64 = (randMax == UInt64.MaxValue);
native32 = (randMax == UInt32.MaxValue);
// Get number of bits to use from Next().
// A RandMax of 2^31-1 gives us 31.
shiftBits = CleromUtil.BitSize(randMax);
shiftMax = UInt64.MaxValue >> (64 - shiftBits);
if (randMax != shiftMax)
{
--shiftBits;
shiftMax >>= 1;
}
// Initialize cache values
ResetCache();
// Useful for confirming properties when debugging
/*
* Console.WriteLine();
* Console.WriteLine("NAME : " + AlgorithmName);
* Console.WriteLine("RandMax : " + randMax);
* Console.WriteLine("RandMax : 0x" + randMax.ToString("X16"));
* Console.WriteLine("Native32 : " + native32);
* Console.WriteLine("Native64 : " + native64);
* Console.WriteLine("BitShift : " + shiftBits);
* Console.WriteLine();
*/
}