include/utils/SkRandom.h - platform/external/skia - Git at Google


 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */


 #ifndef SkRandom_DEFINED
 #define SkRandom_DEFINED

 #include "Sk64.h"
 #include "SkScalar.h"

 /** \class SkRandom

     Utility class that implements pseudo random 32bit numbers using a fast
     linear equation. Unlike rand(), this class holds its own seed (initially
     set to 0), so that multiple instances can be used with no side-effects.
 */
 class SkRandom {
 public:
     SkRandom() : fSeed(0) {}
     SkRandom(uint32_t seed) : fSeed(seed) {}

     /** Return the next pseudo random number as an unsigned 32bit value.
     */
     uint32_t nextU() { uint32_t r = fSeed * kMul + kAdd; fSeed = r; return r; }

     /** Return the next pseudo random number as a signed 32bit value.
     */
     int32_t nextS() { return (int32_t)this->nextU(); }

     /** Return the next pseudo random number as an unsigned 16bit value.
     */
     U16CPU nextU16() { return this->nextU() >> 16; }

     /** Return the next pseudo random number as a signed 16bit value.
     */
     S16CPU nextS16() { return this->nextS() >> 16; }

     /**
      *  Returns value [0...1) as a float
      */
     float nextF() {
         // const is 1 / (2^32 - 1)
         return (float)(this->nextU() * 2.32830644e-10);
     }

     /**
      *  Returns value [min...max) as a float
      */
     float nextRangeF(float min, float max) {
         return min + this->nextF() * (max - min);
     }

     /** Return the next pseudo random number, as an unsigned value of
         at most bitCount bits.
         @param bitCount The maximum number of bits to be returned
     */
     uint32_t nextBits(unsigned bitCount) {
         SkASSERT(bitCount > 0 && bitCount <= 32);
         return this->nextU() >> (32 - bitCount);
     }

     /** Return the next pseudo random unsigned number, mapped to lie within
         [min, max] inclusive.
     */
     uint32_t nextRangeU(uint32_t min, uint32_t max) {
         SkASSERT(min <= max);
         uint32_t range = max - min + 1;
         if (0 == range) {
             return this->nextU();
         } else {
             return min + this->nextU() % range;
         }
     }

     /** Return the next pseudo random unsigned number, mapped to lie within
         [0, count).
      */
     uint32_t nextULessThan(uint32_t count) {
         SkASSERT(count > 0);
         return this->nextRangeU(0, count - 1);
     }

     /** Return the next pseudo random number expressed as an unsigned SkFixed
         in the range [0..SK_Fixed1).
     */
     SkFixed nextUFixed1() { return this->nextU() >> 16; }

     /** Return the next pseudo random number expressed as a signed SkFixed
         in the range (-SK_Fixed1..SK_Fixed1).
     */
     SkFixed nextSFixed1() { return this->nextS() >> 15; }

     /** Return the next pseudo random number expressed as a SkScalar
         in the range [0..SK_Scalar1).
     */
     SkScalar nextUScalar1() { return SkFixedToScalar(this->nextUFixed1()); }

     /** Return the next pseudo random number expressed as a SkScalar
         in the range [min..max).
     */
     SkScalar nextRangeScalar(SkScalar min, SkScalar max) {
         return SkScalarMul(this->nextUScalar1(), (max - min)) + min;
     }

     /** Return the next pseudo random number expressed as a SkScalar
         in the range (-SK_Scalar1..SK_Scalar1).
     */
     SkScalar nextSScalar1() { return SkFixedToScalar(this->nextSFixed1()); }

     /** Return the next pseudo random number as a bool.
     */
     bool nextBool() { return this->nextU() >= 0x80000000; }

     /** A biased version of nextBool().
      */
     bool nextBiasedBool(SkScalar fractionTrue) {
         SkASSERT(fractionTrue >= 0 && fractionTrue <= SK_Scalar1);
         return this->nextUScalar1() <= fractionTrue;
     }

     /** Return the next pseudo random number as a signed 64bit value.
     */
     void next64(Sk64* a) {
         SkASSERT(a);
         a->set(this->nextS(), this->nextU());
     }

     /**
      *  Return the current seed. This allows the caller to later reset to the
      *  same seed (using setSeed) so it can generate the same sequence.
      */
     int32_t getSeed() const { return fSeed; }

     /** Set the seed of the random object. The seed is initialized to 0 when the
         object is first created, and is updated each time the next pseudo random
         number is requested.
     */
     void setSeed(int32_t seed) { fSeed = (uint32_t)seed; }

 private:
     //  See "Numerical Recipes in C", 1992 page 284 for these constants
     enum {
         kMul = 1664525,
         kAdd = 1013904223
     };
     uint32_t fSeed;
 };

 /** \class SkMWCRandom

  Utility class that implements pseudo random 32bit numbers using Marsaglia's
  multiply-with-carry "mother of all" algorithm. Unlike rand(), this class holds
  its own state, so that multiple instances can be used with no side-effects.

  Has a large period and all bits are well-randomized.
  */
 class SkMWCRandom {
 public:
     SkMWCRandom() { init(0); }
     SkMWCRandom(uint32_t seed) { init(seed); }
     SkMWCRandom(const SkMWCRandom& rand) : fK(rand.fK), fJ(rand.fJ) {}

     SkMWCRandom& operator=(const SkMWCRandom& rand) {
         fK = rand.fK;
         fJ = rand.fJ;

         return *this;
     }

     /** Return the next pseudo random number as an unsigned 32bit value.
      */
     uint32_t nextU() {
         fK = kKMul*(fK & 0xffff) + (fK >> 16);
         fJ = kJMul*(fJ & 0xffff) + (fJ >> 16);
         return (((fK << 16) | (fK >> 16)) + fJ);
     }

     /** Return the next pseudo random number as a signed 32bit value.
      */
     int32_t nextS() { return (int32_t)this->nextU(); }

     /** Return the next pseudo random number as an unsigned 16bit value.
      */
     U16CPU nextU16() { return this->nextU() >> 16; }

     /** Return the next pseudo random number as a signed 16bit value.
      */
     S16CPU nextS16() { return this->nextS() >> 16; }

     /**
      *  Returns value [0...1) as an IEEE float
      */
     float nextF() {
         unsigned int floatint = 0x3f800000 | (this->nextU() >> 9);
         float f = *(float*)(&floatint) - 1.0f;
         return f;
     }

     /**
      *  Returns value [min...max) as a float
      */
     float nextRangeF(float min, float max) {
         return min + this->nextF() * (max - min);
     }

     /** Return the next pseudo random number, as an unsigned value of
      at most bitCount bits.
      @param bitCount The maximum number of bits to be returned
      */
     uint32_t nextBits(unsigned bitCount) {
         SkASSERT(bitCount > 0 && bitCount <= 32);
         return this->nextU() >> (32 - bitCount);
     }

     /** Return the next pseudo random unsigned number, mapped to lie within
      [min, max] inclusive.
      */
     uint32_t nextRangeU(uint32_t min, uint32_t max) {
         SkASSERT(min <= max);
         uint32_t range = max - min + 1;
         if (0 == range) {
             return this->nextU();
         } else {
             return min + this->nextU() % range;
         }
     }

     /** Return the next pseudo random unsigned number, mapped to lie within
      [0, count).
      */
     uint32_t nextULessThan(uint32_t count) {
         SkASSERT(count > 0);
         return this->nextRangeU(0, count - 1);
     }

     /** Return the next pseudo random number expressed as an unsigned SkFixed
      in the range [0..SK_Fixed1).
      */
     SkFixed nextUFixed1() { return this->nextU() >> 16; }

     /** Return the next pseudo random number expressed as a signed SkFixed
      in the range (-SK_Fixed1..SK_Fixed1).
      */
     SkFixed nextSFixed1() { return this->nextS() >> 15; }

     /** Return the next pseudo random number expressed as a SkScalar
      in the range [0..SK_Scalar1).
      */
     SkScalar nextUScalar1() { return SkFixedToScalar(this->nextUFixed1()); }

     /** Return the next pseudo random number expressed as a SkScalar
      in the range [min..max).
      */
     SkScalar nextRangeScalar(SkScalar min, SkScalar max) {
         return SkScalarMul(this->nextUScalar1(), (max - min)) + min;
     }

     /** Return the next pseudo random number expressed as a SkScalar
      in the range (-SK_Scalar1..SK_Scalar1).
      */
     SkScalar nextSScalar1() { return SkFixedToScalar(this->nextSFixed1()); }

     /** Return the next pseudo random number as a bool.
      */
     bool nextBool() { return this->nextU() >= 0x80000000; }

     /** A biased version of nextBool().
      */
     bool nextBiasedBool(SkScalar fractionTrue) {
         SkASSERT(fractionTrue >= 0 && fractionTrue <= SK_Scalar1);
         return this->nextUScalar1() <= fractionTrue;
     }

     /** Return the next pseudo random number as a signed 64bit value.
      */
     void next64(Sk64* a) {
         SkASSERT(a);
         a->set(this->nextS(), this->nextU());
     }

     /** Reset the random object.
      */
     void setSeed(uint32_t seed) { init(seed); }

 private:
     // Initialize state variables with LCG.
     // We must ensure that both J and K are non-zero, otherwise the
     // multiply-with-carry step will forevermore return zero.
     void init(uint32_t seed) {
         fK = NextLCG(seed);
         if (0 == fK) {
             fK = NextLCG(fK);
         }
         fJ = NextLCG(fK);
         if (0 == fJ) {
             fJ = NextLCG(fJ);
         }
         SkASSERT(0 != fK && 0 != fJ);
     }
     static uint32_t NextLCG(uint32_t seed) { return kMul*seed + kAdd; }

     //  See "Numerical Recipes in C", 1992 page 284 for these constants
     //  For the LCG that sets the initial state from a seed
     enum {
         kMul = 1664525,
         kAdd = 1013904223
     };
     // Constants for the multiply-with-carry steps
     enum {
         kKMul = 30345,
         kJMul = 18000,
     };

     uint32_t fK;
     uint32_t fJ;
 };

 #endif

	/*
	* Copyright 2006 The Android Open Source Project
	*
	* Use of this source code is governed by a BSD-style license that can be
	* found in the LICENSE file.
	*/


	#ifndef SkRandom_DEFINED
	#define SkRandom_DEFINED

	#include "Sk64.h"
	#include "SkScalar.h"

	/** \class SkRandom

	Utility class that implements pseudo random 32bit numbers using a fast
	linear equation. Unlike rand(), this class holds its own seed (initially
	set to 0), so that multiple instances can be used with no side-effects.
	*/
	class SkRandom {
	public:
	SkRandom() : fSeed(0) {}
	SkRandom(uint32_t seed) : fSeed(seed) {}

	/** Return the next pseudo random number as an unsigned 32bit value.
	*/
	uint32_t nextU() { uint32_t r = fSeed * kMul + kAdd; fSeed = r; return r; }

	/** Return the next pseudo random number as a signed 32bit value.
	*/
	int32_t nextS() { return (int32_t)this->nextU(); }

	/** Return the next pseudo random number as an unsigned 16bit value.
	*/
	U16CPU nextU16() { return this->nextU() >> 16; }

	/** Return the next pseudo random number as a signed 16bit value.
	*/
	S16CPU nextS16() { return this->nextS() >> 16; }

	/**
	* Returns value [0...1) as a float
	*/
	float nextF() {
	// const is 1 / (2^32 - 1)
	return (float)(this->nextU() * 2.32830644e-10);
	}

	/**
	* Returns value [min...max) as a float
	*/
	float nextRangeF(float min, float max) {
	return min + this->nextF() * (max - min);
	}

	/** Return the next pseudo random number, as an unsigned value of
	at most bitCount bits.
	@param bitCount The maximum number of bits to be returned
	*/
	uint32_t nextBits(unsigned bitCount) {
	SkASSERT(bitCount > 0 && bitCount <= 32);
	return this->nextU() >> (32 - bitCount);
	}

	/** Return the next pseudo random unsigned number, mapped to lie within
	[min, max] inclusive.
	*/
	uint32_t nextRangeU(uint32_t min, uint32_t max) {
	SkASSERT(min <= max);
	uint32_t range = max - min + 1;
	if (0 == range) {
	return this->nextU();
	} else {
	return min + this->nextU() % range;
	}
	}

	/** Return the next pseudo random unsigned number, mapped to lie within
	[0, count).
	*/
	uint32_t nextULessThan(uint32_t count) {
	SkASSERT(count > 0);
	return this->nextRangeU(0, count - 1);
	}

	/** Return the next pseudo random number expressed as an unsigned SkFixed
	in the range [0..SK_Fixed1).
	*/
	SkFixed nextUFixed1() { return this->nextU() >> 16; }

	/** Return the next pseudo random number expressed as a signed SkFixed
	in the range (-SK_Fixed1..SK_Fixed1).
	*/
	SkFixed nextSFixed1() { return this->nextS() >> 15; }

	/** Return the next pseudo random number expressed as a SkScalar
	in the range [0..SK_Scalar1).
	*/
	SkScalar nextUScalar1() { return SkFixedToScalar(this->nextUFixed1()); }

	/** Return the next pseudo random number expressed as a SkScalar
	in the range [min..max).
	*/
	SkScalar nextRangeScalar(SkScalar min, SkScalar max) {
	return SkScalarMul(this->nextUScalar1(), (max - min)) + min;
	}

	/** Return the next pseudo random number expressed as a SkScalar
	in the range (-SK_Scalar1..SK_Scalar1).
	*/
	SkScalar nextSScalar1() { return SkFixedToScalar(this->nextSFixed1()); }

	/** Return the next pseudo random number as a bool.
	*/
	bool nextBool() { return this->nextU() >= 0x80000000; }

	/** A biased version of nextBool().
	*/
	bool nextBiasedBool(SkScalar fractionTrue) {
	SkASSERT(fractionTrue >= 0 && fractionTrue <= SK_Scalar1);
	return this->nextUScalar1() <= fractionTrue;
	}

	/** Return the next pseudo random number as a signed 64bit value.
	*/
	void next64(Sk64* a) {
	SkASSERT(a);
	a->set(this->nextS(), this->nextU());
	}

	/**
	* Return the current seed. This allows the caller to later reset to the
	* same seed (using setSeed) so it can generate the same sequence.
	*/
	int32_t getSeed() const { return fSeed; }

	/** Set the seed of the random object. The seed is initialized to 0 when the
	object is first created, and is updated each time the next pseudo random
	number is requested.
	*/
	void setSeed(int32_t seed) { fSeed = (uint32_t)seed; }

	private:
	// See "Numerical Recipes in C", 1992 page 284 for these constants
	enum {
	kMul = 1664525,
	kAdd = 1013904223
	};
	uint32_t fSeed;
	};

	/** \class SkMWCRandom

	Utility class that implements pseudo random 32bit numbers using Marsaglia's
	multiply-with-carry "mother of all" algorithm. Unlike rand(), this class holds
	its own state, so that multiple instances can be used with no side-effects.

	Has a large period and all bits are well-randomized.
	*/
	class SkMWCRandom {
	public:
	SkMWCRandom() { init(0); }
	SkMWCRandom(uint32_t seed) { init(seed); }
	SkMWCRandom(const SkMWCRandom& rand) : fK(rand.fK), fJ(rand.fJ) {}

	SkMWCRandom& operator=(const SkMWCRandom& rand) {
	fK = rand.fK;
	fJ = rand.fJ;

	return *this;
	}

	/** Return the next pseudo random number as an unsigned 32bit value.
	*/
	uint32_t nextU() {
	fK = kKMul*(fK & 0xffff) + (fK >> 16);
	fJ = kJMul*(fJ & 0xffff) + (fJ >> 16);
	return (((fK << 16) \| (fK >> 16)) + fJ);
	}

	/** Return the next pseudo random number as a signed 32bit value.
	*/
	int32_t nextS() { return (int32_t)this->nextU(); }

	/** Return the next pseudo random number as an unsigned 16bit value.
	*/
	U16CPU nextU16() { return this->nextU() >> 16; }

	/** Return the next pseudo random number as a signed 16bit value.
	*/
	S16CPU nextS16() { return this->nextS() >> 16; }

	/**
	* Returns value [0...1) as an IEEE float
	*/
	float nextF() {
	unsigned int floatint = 0x3f800000 \| (this->nextU() >> 9);
	float f = (float)(&floatint) - 1.0f;
	return f;
	}

	/**
	* Returns value [min...max) as a float
	*/
	float nextRangeF(float min, float max) {
	return min + this->nextF() * (max - min);
	}

	/** Return the next pseudo random number, as an unsigned value of
	at most bitCount bits.
	@param bitCount The maximum number of bits to be returned
	*/
	uint32_t nextBits(unsigned bitCount) {
	SkASSERT(bitCount > 0 && bitCount <= 32);
	return this->nextU() >> (32 - bitCount);
	}

	/** Return the next pseudo random unsigned number, mapped to lie within
	[min, max] inclusive.
	*/
	uint32_t nextRangeU(uint32_t min, uint32_t max) {
	SkASSERT(min <= max);
	uint32_t range = max - min + 1;
	if (0 == range) {
	return this->nextU();
	} else {
	return min + this->nextU() % range;
	}
	}

	/** Return the next pseudo random unsigned number, mapped to lie within
	[0, count).
	*/
	uint32_t nextULessThan(uint32_t count) {
	SkASSERT(count > 0);
	return this->nextRangeU(0, count - 1);
	}

	/** Return the next pseudo random number expressed as an unsigned SkFixed
	in the range [0..SK_Fixed1).
	*/
	SkFixed nextUFixed1() { return this->nextU() >> 16; }

	/** Return the next pseudo random number expressed as a signed SkFixed
	in the range (-SK_Fixed1..SK_Fixed1).
	*/
	SkFixed nextSFixed1() { return this->nextS() >> 15; }

	/** Return the next pseudo random number expressed as a SkScalar
	in the range [0..SK_Scalar1).
	*/
	SkScalar nextUScalar1() { return SkFixedToScalar(this->nextUFixed1()); }

	/** Return the next pseudo random number expressed as a SkScalar
	in the range [min..max).
	*/
	SkScalar nextRangeScalar(SkScalar min, SkScalar max) {
	return SkScalarMul(this->nextUScalar1(), (max - min)) + min;
	}

	/** Return the next pseudo random number expressed as a SkScalar
	in the range (-SK_Scalar1..SK_Scalar1).
	*/
	SkScalar nextSScalar1() { return SkFixedToScalar(this->nextSFixed1()); }

	/** Return the next pseudo random number as a bool.
	*/
	bool nextBool() { return this->nextU() >= 0x80000000; }

	/** A biased version of nextBool().
	*/
	bool nextBiasedBool(SkScalar fractionTrue) {
	SkASSERT(fractionTrue >= 0 && fractionTrue <= SK_Scalar1);
	return this->nextUScalar1() <= fractionTrue;
	}

	/** Return the next pseudo random number as a signed 64bit value.
	*/
	void next64(Sk64* a) {
	SkASSERT(a);
	a->set(this->nextS(), this->nextU());
	}

	/** Reset the random object.
	*/
	void setSeed(uint32_t seed) { init(seed); }

	private:
	// Initialize state variables with LCG.
	// We must ensure that both J and K are non-zero, otherwise the
	// multiply-with-carry step will forevermore return zero.
	void init(uint32_t seed) {
	fK = NextLCG(seed);
	if (0 == fK) {
	fK = NextLCG(fK);
	}
	fJ = NextLCG(fK);
	if (0 == fJ) {
	fJ = NextLCG(fJ);
	}
	SkASSERT(0 != fK && 0 != fJ);
	}
	static uint32_t NextLCG(uint32_t seed) { return kMul*seed + kAdd; }

	// See "Numerical Recipes in C", 1992 page 284 for these constants
	// For the LCG that sets the initial state from a seed
	enum {
	kMul = 1664525,
	kAdd = 1013904223
	};
	// Constants for the multiply-with-carry steps
	enum {
	kKMul = 30345,
	kJMul = 18000,
	};

	uint32_t fK;
	uint32_t fJ;
	};

	#endif