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170 lines
6.5 KiB
170 lines
6.5 KiB
#include "pch.hxx"
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#include "randpeak.hxx"
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/////////////////////////////////////////////////////////////////////////////
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// //
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// randpeak.c -- Functions to provide 32-bit random numbers, including //
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// a linear distribution (Random32 and RandomInRange), //
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// and a peaked distribution (RandomPeaked). //
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// //
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// Assumptions: ULONG is 32-bit unsigned data type, and //
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// BOOL is an integral boolean type. //
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// //
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// If MULTITHREADED is defined, critical //
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// section primitives must be defined and //
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// supported. //
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// //
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// Two's complement wraparound (mod 2^32) //
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// occurs on addition and multiplication //
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// where result is greater than (2^32-1) //
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// //
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// Author: Tom McGuire (tommcg), 03/29/94 //
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// //
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// (C) Copyright 1994, Microsoft Corporation //
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// //
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/////////////////////////////////////////////////////////////////////////////
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#define MULTIPLIER ((ULONG) 1664525 ) // From Knuth. Guarantees 2^32 non-
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// repeating values.
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ULONG ulInternalSeed;
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ULONG ulInternalAdder;
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#ifdef MULTITHREADED
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CRITICAL_SECTION ulInternalSeedCritSect;
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BOOL bInternalSeedCritSectInitialized;
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#endif
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ULONG BitReverse32( ULONG ulNumber ) {
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ULONG ulNewValue = 0;
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ULONG ulReadMask = 0x00000001;
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ULONG ulWriteBit = 0x80000000;
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do {
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if ( ulNumber & ulReadMask )
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ulNewValue |= ulWriteBit;
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ulReadMask <<= 1;
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ulWriteBit >>= 1;
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}
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while ( ulWriteBit );
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return ulNewValue;
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}
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void SeedRandom32( ULONG ulSeed ) {
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//
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// Assume this is called from a single thread only before any calls
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// to Random32(), RandomInRange(), or RandomPeaked().
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//
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#ifdef MULTITHREADED
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if ( ! bInternalSeedCritSectInitialized ) {
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InitializeCriticalSection( &ulInternalSeedCritSect );
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bInternalSeedCritSectInitialized = TRUE;
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}
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#endif
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ulInternalSeed = ulSeed;
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ulInternalAdder = ((( ulSeed ^ 0xFFFFFFFF ) | 0x00000001 ) & 0x7FFFFFFF );
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}
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ULONG Random32( void ) {
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ULONG ulRand;
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#ifdef MULTITHREADED
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EnterCriticalSection( &ulInternalSeedCritSect );
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#endif
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ulRand = ( ulInternalSeed * MULTIPLIER ) + ulInternalAdder;
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ulInternalSeed = ulRand;
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#ifdef MULTITHREADED
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LeaveCriticalSection( &ulInternalSeedCritSect );
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#endif
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return BitReverse32( ulRand );
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}
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ULONG RandomInRange( ULONG ulMinInclusive, ULONG ulMaxInclusive ) {
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ULONG ulRange = ( ulMaxInclusive - ulMinInclusive + 1 );
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ULONG ulRand = Random32();
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if ( ulRange )
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ulRand %= ulRange;
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return ( ulRand + ulMinInclusive );
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}
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ULONG RandomPeaked( ULONG ulMaxInclusive,
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ULONG ulPeakFrequency,
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ULONG ulPeakWidth,
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ULONG ulPeakDensity,
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ULONG ulPeakDecay ) {
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ULONG ulWhichPeak, ulPeakValue, ulRange, ulHigh, ulLow;
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ulWhichPeak = ( ulMaxInclusive / ulPeakFrequency );
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do {
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ulWhichPeak = RandomInRange( 0, ulWhichPeak );
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}
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while ( ulPeakDecay-- );
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ulPeakValue = ulWhichPeak * ulPeakFrequency;
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ulRange = ( ulPeakFrequency * ( ulPeakDensity + 1 )) / ( ulPeakDensity + 2 );
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while ( ulPeakDensity-- )
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ulRange = RandomInRange( ulPeakWidth / 2, ulRange );
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ulLow = ( ulPeakValue > ulRange ) ? ( ulPeakValue - ulRange ) : 0;
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ulHigh = ( ulPeakValue + ulRange );
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if ( ulHigh > ulMaxInclusive )
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ulHigh = ulMaxInclusive;
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ulPeakValue = RandomInRange( ulLow, ulHigh );
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return ulPeakValue;
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}
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/////////////////////////////////////////////////////////////////////////////
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// //
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// | Peaked Distribution | //
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// |_ | //
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// | \ | //
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// | \ _ | //
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// | \ / \ _ | //
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// | \ / \ / \ _ | //
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// | \ / \ / \ / \ _| //
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// | \_____/ \________/ \__ __/ \____________/ | //
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// |_______________________________________________________________| //
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// 0 P 2P nP Max //
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// //
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// The center of each peak occurs at ulPeakFreq intervals starting //
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// from zero, and the tops of the peaks are linear-distributed across //
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// ulPeakWidth (ie, +/- ulPeakWidth/2). ulPeakDensity controls the //
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// slope of the distribution off each peak with higher numbers causing //
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// steeper slopes (and hence wider, lower valleys). ulPeakDecay //
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// controls the declining peak-to-peak slope with higher numbers //
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// causing higher peaks near zero and lower peaks toward ulMax. //
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// Note that ulPeakDensity and ulPeakDecay are computationally //
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// expensive with higher values (they represent internal iteration //
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// counts), so moderate numbers such as 3-5 for ulPeakDensity and //
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// 1-2 for ulPeakDecay are recommended. //
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// //
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/////////////////////////////////////////////////////////////////////////////
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