Move random from core to utils

Review URL: https://codereview.appspot.com/7193064

git-svn-id: http://skia.googlecode.com/svn/trunk@7395 2bbb7eff-a529-9590-31e7-b0007b416f81

1 files changed, 150 insertions, 0 deletions

diff --git a/include/utils/SkRandom.h b/include/utils/SkRandom.h
new file mode 100644
index 0000000000..73dc4917d7
--- /dev/null
+++ b/include/utils/SkRandom.h
@@ -0,0 +1,150 @@
+
+/*
+ * 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);
+        return min + this->nextU() % (max - min + 1);
+    }
+
+    /** 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
+