skia2/include/core/SkRandom.h
reed@android.com 8a1c16ff38 grab from latest android
git-svn-id: http://skia.googlecode.com/svn/trunk@27 2bbb7eff-a529-9590-31e7-b0007b416f81
2008-12-17 15:59:43 +00:00

111 lines
3.5 KiB
C++

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