using System;
using HeuristicLab.Common;
using HeuristicLab.Core;
using HEAL.Attic;
namespace HeuristicLab.Random {
///
/// A fast random number generator for .NET
/// Colin Green, January 2005
///
/// September 4th 2005
/// Added NextBytesUnsafe() - commented out by default.
/// Fixed bug in Reinitialise() - y,z and w variables were not being reset.
///
/// 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/xorshift.pdf
///
/// 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 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 each 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.
///
/// August 2010:
/// adapted for HeuristicLab by gkronber (cloning, persistence, IRandom interface)
///
///
[StorableType("BC86BFF3-80B5-4C77-9D8C-B29576032634")]
public sealed class FastRandom : Item, IRandom {
// The +1 ensures NextDouble doesn't generate 1.0
private const double REAL_UNIT_INT = 1.0 / ((double)int.MaxValue + 1.0);
private const double REAL_UNIT_UINT = 1.0 / ((double)uint.MaxValue + 1.0);
private const uint Y = 842502087, Z = 3579807591, W = 273326509;
[Storable]
private uint x, y, z, w;
#region Constructors
///
/// Used by HeuristicLab.Persistence to initialize new instances during deserialization.
///
/// true, if the constructor is called during deserialization.
[StorableConstructor]
private FastRandom(StorableConstructorFlag _) : base(_) { }
///
/// Initializes a new instance from an existing one (copy constructor).
///
/// The original instance which is used to initialize the new instance.
/// A which is used to track all already cloned objects in order to avoid cycles.
private FastRandom(FastRandom original, Cloner cloner)
: base(original, cloner) {
x = original.x;
y = original.y;
z = original.z;
w = original.w;
bitBuffer = original.bitBuffer;
bitMask = original.bitMask;
}
///
/// Initialises a new instance using time dependent seed.
///
public FastRandom() {
// Initialise using the system tick count.
Reinitialise((int)Environment.TickCount);
}
///
/// 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) {
Reinitialise(seed);
}
#endregion
#region Public Methods [Reinitialisation]
///
/// Reinitialises using an int value as a seed.
///
///
public void Reinitialise(int seed) {
// The only stipulation stated for the xorshift RNG is that at least one of
// the seeds x,y,z,w is non-zero. We fulfill that requirement by only allowing
// resetting of the x seed
x = (uint)seed;
y = Y;
z = Z;
w = W;
}
#endregion
#region Public Methods [System.Random functionally equivalent methods]
///
/// 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 int Next() {
uint t = (x ^ (x << 11));
x = y; y = z; z = w;
w = (w ^ (w >> 19)) ^ (t ^ (t >> 8));
// Handle the special case where the value int.MaxValue is generated. This is outside of
// the range of permitted values, so we therefore call Next() to try again.
uint rtn = w & 0x7FFFFFFF;
if (rtn == 0x7FFFFFFF)
return Next();
return (int)rtn;
}
///
/// Generates a random int over the range 0 to upperBound-1, and not including upperBound.
///
///
///
public int Next(int upperBound) {
if (upperBound < 0)
throw new ArgumentOutOfRangeException("upperBound", upperBound, "upperBound must be >=0");
uint t = (x ^ (x << 11));
x = y; y = z; z = w;
// The explicit int cast before the first multiplication gives better performance.
// See comments in NextDouble.
return (int)((REAL_UNIT_INT * (int)(0x7FFFFFFF & (w = (w ^ (w >> 19)) ^ (t ^ (t >> 8))))) * upperBound);
}
///
/// Generates a random int over the range lowerBound to upperBound-1, and not including upperBound.
/// upperBound must be >= lowerBound. lowerBound may be negative.
///
///
///
///
public int Next(int lowerBound, int upperBound) {
if (lowerBound > upperBound)
throw new ArgumentOutOfRangeException("upperBound", upperBound, "upperBound must be >=lowerBound");
uint t = (x ^ (x << 11));
x = y; y = z; z = w;
// The explicit int cast before the first multiplication gives better performance.
// See comments in NextDouble.
int range = upperBound - lowerBound;
if (range < 0) { // If range is <0 then an overflow has occured and must resort to using long integer arithmetic instead (slower).
// We also must use all 32 bits of precision, instead of the normal 31, which again is slower.
return lowerBound + (int)((REAL_UNIT_UINT * (double)(w = (w ^ (w >> 19)) ^ (t ^ (t >> 8)))) * (double)((long)upperBound - (long)lowerBound));
}
// 31 bits of precision will suffice if range<=int.MaxValue. This allows us to cast to an int and gain
// a little more performance.
return lowerBound + (int)((REAL_UNIT_INT * (double)(int)(0x7FFFFFFF & (w = (w ^ (w >> 19)) ^ (t ^ (t >> 8))))) * (double)range);
}
///
/// Generates a random double. Values returned are from 0.0 up to but not including 1.0.
///
///
public double NextDouble() {
uint t = (x ^ (x << 11));
x = y; y = z; z = w;
// Here we can gain a 2x speed improvement by generating a value that can be cast to
// an int instead of the more easily available uint. If we then explicitly cast to an
// int the compiler will then cast the int to a double to perform the multiplication,
// this final cast is a lot faster than casting from a uint to a double. The extra cast
// to an int is very fast (the allocated bits remain the same) and so the overall effect
// of the extra cast is a significant performance improvement.
//
// Also note that the loss of one bit of precision is equivalent to what occurs within
// System.Random.
return (REAL_UNIT_INT * (int)(0x7FFFFFFF & (w = (w ^ (w >> 19)) ^ (t ^ (t >> 8)))));
}
///
/// Fills the provided byte array with random bytes.
/// This method is functionally equivalent to System.Random.NextBytes().
///
///
public void NextBytes(byte[] buffer) {
// Fill up the bulk of the buffer in chunks of 4 bytes at a time.
uint x = this.x, y = this.y, z = this.z, w = this.w;
int i = 0;
uint t;
for (int bound = buffer.Length - 3; i < bound; ) {
// Generate 4 bytes.
// Increased performance is achieved by generating 4 random bytes per loop.
// Also note that no mask needs to be applied to zero out the higher order bytes before
// casting because the cast ignores thos bytes. Thanks to Stefan Trosch�tz for pointing this out.
t = (x ^ (x << 11));
x = y; y = z; z = w;
w = (w ^ (w >> 19)) ^ (t ^ (t >> 8));
buffer[i++] = (byte)w;
buffer[i++] = (byte)(w >> 8);
buffer[i++] = (byte)(w >> 16);
buffer[i++] = (byte)(w >> 24);
}
// Fill up any remaining bytes in the buffer.
if (i < buffer.Length) {
// Generate 4 bytes.
t = (x ^ (x << 11));
x = y; y = z; z = w;
w = (w ^ (w >> 19)) ^ (t ^ (t >> 8));
buffer[i++] = (byte)w;
if (i < buffer.Length) {
buffer[i++] = (byte)(w >> 8);
if (i < buffer.Length) {
buffer[i++] = (byte)(w >> 16);
if (i < buffer.Length) {
buffer[i] = (byte)(w >> 24);
}
}
}
}
this.x = x; this.y = y; this.z = z; this.w = w;
}
// ///
// /// A version of NextBytes that uses a pointer to set 4 bytes of the byte buffer in one operation
// /// thus providing a nice speedup. The loop is also partially unrolled to allow out-of-order-execution,
// /// this results in about a x2 speedup on an AMD Athlon. Thus performance may vary wildly on different CPUs
// /// depending on the number of execution units available.
// ///
// /// Another significant speedup is obtained by setting the 4 bytes by indexing pDWord (e.g. pDWord[i++]=w)
// /// instead of adjusting it dereferencing it (e.g. *pDWord++=w).
// ///
// /// Note that this routine requires the unsafe compilation flag to be specified and so is commented out by default.
// ///
// ///
// public unsafe void NextBytesUnsafe(byte[] buffer)
// {
// if(buffer.Length % 8 != 0)
// throw new ArgumentException("Buffer length must be divisible by 8", "buffer");
//
// uint x=this.x, y=this.y, z=this.z, w=this.w;
//
// fixed(byte* pByte0 = buffer)
// {
// uint* pDWord = (uint*)pByte0;
// for(int i=0, len=buffer.Length>>2; i < len; i+=2)
// {
// uint t=(x^(x<<11));
// x=y; y=z; z=w;
// pDWord[i] = w = (w^(w>>19))^(t^(t>>8));
//
// t=(x^(x<<11));
// x=y; y=z; z=w;
// pDWord[i+1] = w = (w^(w>>19))^(t^(t>>8));
// }
// }
//
// this.x=x; this.y=y; this.z=z; this.w=w;
// }
#endregion
#region Public Methods [Methods not present on System.Random]
///
/// 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 uint NextUInt() {
uint t = (x ^ (x << 11));
x = y; y = z; z = w;
return (w = (w ^ (w >> 19)) ^ (t ^ (t >> 8)));
}
///
/// 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 int NextInt() {
uint t = (x ^ (x << 11));
x = y; y = z; z = w;
return (int)(0x7FFFFFFF & (w = (w ^ (w >> 19)) ^ (t ^ (t >> 8))));
}
///
/// 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 bool NextBool() {
if (bitMask == 1) {
// Generate 32 more bits.
uint t = (x ^ (x << 11));
x = y; y = z; z = w;
bitBuffer = w = (w ^ (w >> 19)) ^ (t ^ (t >> 8));
// Reset the bitMask that tells us which bit to read next.
bitMask = 0x80000000;
return (bitBuffer & bitMask) == 0;
}
return (bitBuffer & (bitMask >>= 1)) == 0;
}
// Buffer 32 bits in bitBuffer, return 1 at a time, keep track of how many have been returned
// with bitBufferIdx.
[Storable]
private uint bitBuffer;
[Storable]
private uint bitMask = 1;
#endregion
#region IRandom Members
public void Reset() {
Reinitialise((int)Environment.TickCount);
}
public void Reset(int seed) {
Reinitialise(seed);
}
#endregion
public override IDeepCloneable Clone(Cloner cloner) {
return new FastRandom(this, cloner);
}
}
}