| /* |
| * 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 <cstdint> |
| |
| 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 |