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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/private/base/SkAssert.h" #include "include/private/base/SkFixed.h" #include "include/private/base/SkFloatBits.h" #include typedef float SkScalar; /** \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() { int floatint = 0x3f800000 | (int)(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 <= 1); 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