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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 "include/core/SkScalar.h"
- #include "include/private/SkFixed.h"
- #include "include/private/SkFloatBits.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(); }
- /**
- * 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;
- }
- /** 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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