C# Class SharpNeat.Utility.FastRandom

A fast random number generator for .NET Colin Green, January 2005 Key points: 1) Based on a simple and fast xor-shift pseudo random number generator (RNG) specified in: Marsaglia, George. (2003). Xorshift RNGs. http://www.jstatsoft.org/v08/i14/paper This particular implementation of xorshift has a period of 2^128-1. See the above paper to see how this can be easily extened if you need a longer period. At the time of writing I could find no information on the period of System.Random for comparison. 2) Faster than System.Random. Up to 8x faster, depending on which methods are called. 3) Direct replacement for System.Random. This class implements all of the methods that System.Random does plus some additional methods. The like named methods are functionally equivalent. 4) Allows fast re-initialisation with a seed, unlike System.Random which accepts a seed at construction time which then executes a relatively expensive initialisation routine. This provides a vast speed improvement if you need to reset the pseudo-random number sequence many times, e.g. if you want to re-generate the same sequence of random numbers many times. An alternative might be to cache random numbers in an array, but that approach is limited by memory capacity and the fact that you may also want a large number of different sequences cached. Each sequence can be represented by a single seed value (int) when using FastRandom. Notes. A further performance improvement can be obtained by declaring local variables as static, thus avoiding re-allocation of variables on each call. However care should be taken if multiple instances of FastRandom are in use or if being used in a multi-threaded environment. Colin Green, September 4th 2005 - Added NextBytesUnsafe() - commented out by default. - Fixed bug in Reinitialise() - y,z and w variables were not being reset. Colin Green, December 2008. - Fix to Next() - Was previously able to return int.MaxValue, contrary to the method's contract and comments. - Modified NextBool() to use _bitMask instead of a count of remaining bits. Also reset the bit buffer in Reinitialise(). Colin Green, 2011-08-31 - Added NextByte() method. - Added new statically declared seedRng FastRandom to allow easy creation of multiple FastRandoms with different seeds within a single clock tick. Colin Green, 2011-10-04 - Seeds are now hashed. Without this the first random sample for nearby seeds (1,2,3, etc.) are very similar (have a similar bit pattern). Thanks to Francois Guibert for identifying this problem.
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Public Methods

Method Description
FastRandom ( ) : System

Initialises a new instance using time dependent seed.
FastRandom ( int seed ) : System

Initialises a new instance using an int value as seed. This constructor signature is provided to maintain compatibility with System.Random
Next ( ) : int

Generates a random int over the range 0 to int.MaxValue-1. MaxValue is not generated in order to remain functionally equivalent to System.Random.Next(). This does slightly eat into some of the performance gain over System.Random, but not much. For better performance see: Call NextInt() for an int over the range 0 to int.MaxValue. Call NextUInt() and cast the result to an int to generate an int over the full Int32 value range including negative values.
Next ( int upperBound ) : int

Generates a random int over the range 0 to upperBound-1, and not including upperBound.
Next ( int lowerBound, int upperBound ) : int

Generates a random int over the range lowerBound to upperBound-1, and not including upperBound. upperBound must be >= lowerBound. lowerBound may be negative.
NextBool ( ) : bool

Generates a single random bit. This method's performance is improved by generating 32 bits in one operation and storing them ready for future calls.
NextBytes ( byte buffer ) : void

Fills the provided byte array with random bytes. This method is functionally equivalent to System.Random.NextBytes().
NextDouble ( ) : double

Generates a random double. Values returned are from 0.0 up to but not including 1.0.
NextInt ( ) : int

Generates a random int over the range 0 to int.MaxValue, inclusive. This method differs from Next() only in that the range is 0 to int.MaxValue and not 0 to int.MaxValue-1. The slight difference in range means this method is slightly faster than Next() but is not functionally equivalent to System.Random.Next().
NextUInt ( ) : uint

Generates a uint. Values returned are over the full range of a uint, uint.MinValue to uint.MaxValue, inclusive. This is the fastest method for generating a single random number because the underlying random number generator algorithm generates 32 random bits that can be cast directly to a uint.
Reinitialise ( int seed ) : void

Reinitialises using an int value as a seed.

Method Details

FastRandom() public method

Initialises a new instance using time dependent seed.
public FastRandom ( ) : System
return System

FastRandom() public method

Initialises a new instance using an int value as seed. This constructor signature is provided to maintain compatibility with System.Random
public FastRandom ( int seed ) : System
seed int
return System

Next() public method

Generates a random int over the range 0 to int.MaxValue-1. MaxValue is not generated in order to remain functionally equivalent to System.Random.Next(). This does slightly eat into some of the performance gain over System.Random, but not much. For better performance see: Call NextInt() for an int over the range 0 to int.MaxValue. Call NextUInt() and cast the result to an int to generate an int over the full Int32 value range including negative values.
public Next ( ) : int
return int

Next() public method

Generates a random int over the range 0 to upperBound-1, and not including upperBound.
public Next ( int upperBound ) : int
upperBound int
return int

Next() public method

Generates a random int over the range lowerBound to upperBound-1, and not including upperBound. upperBound must be >= lowerBound. lowerBound may be negative.
public Next ( int lowerBound, int upperBound ) : int
lowerBound int
upperBound int
return int

NextBool() public method

Generates a single random bit. This method's performance is improved by generating 32 bits in one operation and storing them ready for future calls.
public NextBool ( ) : bool
return bool

NextBytes() public method

Fills the provided byte array with random bytes. This method is functionally equivalent to System.Random.NextBytes().
public NextBytes ( byte buffer ) : void
buffer byte
return void

NextDouble() public method

Generates a random double. Values returned are from 0.0 up to but not including 1.0.
public NextDouble ( ) : double
return double

NextInt() public method

Generates a random int over the range 0 to int.MaxValue, inclusive. This method differs from Next() only in that the range is 0 to int.MaxValue and not 0 to int.MaxValue-1. The slight difference in range means this method is slightly faster than Next() but is not functionally equivalent to System.Random.Next().
public NextInt ( ) : int
return int

NextUInt() public method

Generates a uint. Values returned are over the full range of a uint, uint.MinValue to uint.MaxValue, inclusive. This is the fastest method for generating a single random number because the underlying random number generator algorithm generates 32 random bits that can be cast directly to a uint.
public NextUInt ( ) : uint
return uint

Reinitialise() public method

Reinitialises using an int value as a seed.
public Reinitialise ( int seed ) : void
seed int
return void