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/*
* 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 "../private/SkFixed.h"
#include "../private/SkFloatBits.h"
#include "SkScalar.h"
/** \class SkRandom
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 SkRandom {
public:
SkRandom() { init(0); }
SkRandom(uint32_t seed) { init(seed); }
SkRandom(const SkRandom& rand) : fK(rand.fK), fJ(rand.fJ) {}
SkRandom& operator=(const SkRandom& 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 = SkBits2Float(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 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 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.
*/
int64_t next64() {
int64_t hi = this->nextS();
return (hi << 32) | 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; }
/** 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; }
// 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
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