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// ==++==
//
// Copyright (c) Microsoft Corporation. All rights reserved.
//
// ==--==
/*============================================================
**
** Class: Random
**
**
** Purpose: A random number generator.
**
**
===========================================================*/
namespace System {
using System;
using System.Runtime;
using System.Runtime.CompilerServices;
using System.Globalization;
using System.Diagnostics.Contracts;
[System.Runtime.InteropServices.ComVisible(true)]
[Serializable]
public class Random {
//
// Private Constants
//
private const int MBIG = Int32.MaxValue;
private const int MSEED = 161803398;
private const int MZ = 0;
//
// Member Variables
//
private int inext;
private int inextp;
private int[] SeedArray = new int[56];
//
// Public Constants
//
//
// Native Declarations
//
//
// Constructors
//
public Random()
: this(Environment.TickCount) {
}
public Random(int Seed) {
int ii;
int mj, mk;
//Initialize our Seed array.
//This algorithm comes from Numerical Recipes in C (2nd Ed.)
int subtraction = (Seed == Int32.MinValue) ? Int32.MaxValue : Math.Abs(Seed);
mj = MSEED - subtraction;
SeedArray[55]=mj;
mk=1;
for (int i=1; i<55; i++) { //Apparently the range [1..55] is special (Knuth) and so we're wasting the 0'th position.
ii = (21*i)%55;
SeedArray[ii]=mk;
mk = mj - mk;
if (mk<0) mk+=MBIG;
mj=SeedArray[ii];
}
for (int k=1; k<5; k++) {
for (int i=1; i<56; i++) {
SeedArray[i] -= SeedArray[1+(i+30)%55];
if (SeedArray[i]<0) SeedArray[i]+=MBIG;
}
}
inext=0;
inextp = 21;
Seed = 1;
}
//
// Package Private Methods
//
/*====================================Sample====================================
**Action: Return a new random number [0..1) and reSeed the Seed array.
**Returns: A double [0..1)
**Arguments: None
**Exceptions: None
==============================================================================*/
protected virtual double Sample() {
//Including this division at the end gives us significantly improved
//random number distribution.
return (InternalSample()*(1.0/MBIG));
}
private int InternalSample() {
int retVal;
int locINext = inext;
int locINextp = inextp;
if (++locINext >=56) locINext=1;
if (++locINextp>= 56) locINextp = 1;
retVal = SeedArray[locINext]-SeedArray[locINextp];
if (retVal == MBIG) retVal--;
if (retVal<0) retVal+=MBIG;
SeedArray[locINext]=retVal;
inext = locINext;
inextp = locINextp;
return retVal;
}
//
// Public Instance Methods
//
/*=====================================Next=====================================
**Returns: An int [0..Int32.MaxValue)
**Arguments: None
**Exceptions: None.
==============================================================================*/
public virtual int Next() {
return InternalSample();
}
private double GetSampleForLargeRange() {
// The distribution of double value returned by Sample
// is not distributed well enough for a large range.
// If we use Sample for a range [Int32.MinValue..Int32.MaxValue)
// We will end up getting even numbers only.
int result = InternalSample();
// Note we can't use addition here. The distribution will be bad if we do that.
bool negative = (InternalSample()%2 == 0) ? true : false; // decide the sign based on second sample
if( negative) {
result = -result;
}
double d = result;
d += (Int32.MaxValue - 1); // get a number in range [0 .. 2 * Int32MaxValue - 1)
d /= 2*(uint)Int32.MaxValue - 1 ;
return d;
}
/*=====================================Next=====================================
**Returns: An int [minvalue..maxvalue)
**Arguments: minValue -- the least legal value for the Random number.
** maxValue -- One greater than the greatest legal return value.
**Exceptions: None.
==============================================================================*/
public virtual int Next(int minValue, int maxValue) {
if (minValue>maxValue) {
throw new ArgumentOutOfRangeException("minValue",Environment.GetResourceString("Argument_MinMaxValue", "minValue", "maxValue"));
}
Contract.EndContractBlock();
long range = (long)maxValue-minValue;
if( range <= (long)Int32.MaxValue) {
return ((int)(Sample() * range) + minValue);
}
else {
return (int)((long)(GetSampleForLargeRange() * range) + minValue);
}
}
/*=====================================Next=====================================
**Returns: An int [0..maxValue)
**Arguments: maxValue -- One more than the greatest legal return value.
**Exceptions: None.
==============================================================================*/
public virtual int Next(int maxValue) {
if (maxValue<0) {
throw new ArgumentOutOfRangeException("maxValue", Environment.GetResourceString("ArgumentOutOfRange_MustBePositive", "maxValue"));
}
Contract.EndContractBlock();
return (int)(Sample()*maxValue);
}
/*=====================================Next=====================================
**Returns: A double [0..1)
**Arguments: None
**Exceptions: None
==============================================================================*/
public virtual double NextDouble() {
return Sample();
}
/*==================================NextBytes===================================
**Action: Fills the byte array with random bytes [0..0x7f]. The entire array is filled.
**Returns:Void
**Arugments: buffer -- the array to be filled.
**Exceptions: None
==============================================================================*/
public virtual void NextBytes(byte [] buffer){
if (buffer==null) throw new ArgumentNullException("buffer");
Contract.EndContractBlock();
for (int i=0; i<buffer.Length; i++) {
buffer[i]=(byte)(InternalSample()%(Byte.MaxValue+1));
}
}
}
}
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