111 lines
3.5 KiB
C++
111 lines
3.5 KiB
C++
/*
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* Copyright (C) 2006 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef SkRandom_DEFINED
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#define SkRandom_DEFINED
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#include "Sk64.h"
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#include "SkScalar.h"
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/** \class SkRandom
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Utility class that implements pseudo random 32bit numbers using a fast
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linear equation. Unlike rand(), this class holds its own seed (initially
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set to 0), so that multiple instances can be used with no side-effects.
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*/
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class SkRandom {
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public:
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SkRandom() : fSeed(0) {}
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SkRandom(uint32_t seed) : fSeed(seed) {}
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/** Return the next pseudo random number as an unsigned 32bit value.
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*/
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uint32_t nextU() { uint32_t r = fSeed * kMul + kAdd; fSeed = r; return r; }
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/** Return the next pseudo random number as a signed 32bit value.
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*/
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int32_t nextS() { return (int32_t)this->nextU(); }
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/** Return the next pseudo random number as an unsigned 16bit value.
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*/
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U16CPU nextU16() { return this->nextU() >> 16; }
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/** Return the next pseudo random number as a signed 16bit value.
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*/
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S16CPU nextS16() { return this->nextS() >> 16; }
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/** Return the next pseudo random number, as an unsigned value of
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at most bitCount bits.
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@param bitCount The maximum number of bits to be returned
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*/
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uint32_t nextBits(unsigned bitCount) {
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SkASSERT(bitCount > 0 && bitCount <= 32);
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return this->nextU() >> (32 - bitCount);
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}
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/** Return the next pseudo random unsigned number, mapped to lie within
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[min, max] inclusive.
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*/
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uint32_t nextRangeU(uint32_t min, uint32_t max) {
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SkASSERT(min <= max);
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return min + this->nextU() % (max - min + 1);
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}
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/** Return the next pseudo random number expressed as an unsigned SkFixed
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in the range [0..SK_Fixed1).
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*/
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SkFixed nextUFixed1() { return this->nextU() >> 16; }
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/** Return the next pseudo random number expressed as a signed SkFixed
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in the range (-SK_Fixed1..SK_Fixed1).
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*/
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SkFixed nextSFixed1() { return this->nextS() >> 15; }
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/** Return the next pseudo random number expressed as a SkScalar
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in the range [0..SK_Scalar1).
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*/
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SkScalar nextUScalar1() { return SkFixedToScalar(this->nextUFixed1()); }
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/** Return the next pseudo random number expressed as a SkScalar
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in the range (-SK_Scalar1..SK_Scalar1).
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*/
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SkScalar nextSScalar1() { return SkFixedToScalar(this->nextSFixed1()); }
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/** Return the next pseudo random number as a signed 64bit value.
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*/
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void next64(Sk64* a) {
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SkASSERT(a);
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a->set(this->nextS(), this->nextU());
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}
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/** Set the seed of the random object. The seed is initialized to 0 when the
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object is first created, and is updated each time the next pseudo random
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number is requested.
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*/
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void setSeed(int32_t seed) { fSeed = (uint32_t)seed; }
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private:
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// See "Numerical Recipes in C", 1992 page 284 for these constants
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enum {
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kMul = 1664525,
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kAdd = 1013904223
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};
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uint32_t fSeed;
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};
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#endif
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