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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 "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; }
/**
* Returns value [0...1) as a float
*/
float nextF() {
// const is 1 / (2^32 - 1)
return (float)(this->nextU() * 2.32830644e-10);
}
/**
* 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 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 [min..max).
*/
SkScalar nextRangeScalar(SkScalar min, SkScalar max) {
return SkScalarMul(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;
}
/** Return the next pseudo random number as a signed 64bit value.
*/
void next64(Sk64* a) {
SkASSERT(a);
a->set(this->nextS(), this->nextU());
}
/**
* Return the current seed. This allows the caller to later reset to the
* same seed (using setSeed) so it can generate the same sequence.
*/
int32_t getSeed() const { return fSeed; }
/** 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
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