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      1 /*
      2  * Copyright (C) 2006 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #ifndef SkRandom_DEFINED
     18 #define SkRandom_DEFINED
     19 
     20 #include "Sk64.h"
     21 #include "SkScalar.h"
     22 
     23 /** \class SkRandom
     24 
     25     Utility class that implements pseudo random 32bit numbers using a fast
     26     linear equation. Unlike rand(), this class holds its own seed (initially
     27     set to 0), so that multiple instances can be used with no side-effects.
     28 */
     29 class SkRandom {
     30 public:
     31     SkRandom() : fSeed(0) {}
     32     SkRandom(uint32_t seed) : fSeed(seed) {}
     33 
     34     /** Return the next pseudo random number as an unsigned 32bit value.
     35     */
     36     uint32_t nextU() { uint32_t r = fSeed * kMul + kAdd; fSeed = r; return r; }
     37 
     38     /** Return the next pseudo random number as a signed 32bit value.
     39     */
     40     int32_t nextS() { return (int32_t)this->nextU(); }
     41 
     42     /** Return the next pseudo random number as an unsigned 16bit value.
     43     */
     44     U16CPU nextU16() { return this->nextU() >> 16; }
     45 
     46     /** Return the next pseudo random number as a signed 16bit value.
     47     */
     48     S16CPU nextS16() { return this->nextS() >> 16; }
     49 
     50     /** Return the next pseudo random number, as an unsigned value of
     51         at most bitCount bits.
     52         @param bitCount The maximum number of bits to be returned
     53     */
     54     uint32_t nextBits(unsigned bitCount) {
     55         SkASSERT(bitCount > 0 && bitCount <= 32);
     56         return this->nextU() >> (32 - bitCount);
     57     }
     58 
     59     /** Return the next pseudo random unsigned number, mapped to lie within
     60         [min, max] inclusive.
     61     */
     62     uint32_t nextRangeU(uint32_t min, uint32_t max) {
     63         SkASSERT(min <= max);
     64         return min + this->nextU() % (max - min + 1);
     65     }
     66 
     67     /** Return the next pseudo random number expressed as an unsigned SkFixed
     68         in the range [0..SK_Fixed1).
     69     */
     70     SkFixed nextUFixed1() { return this->nextU() >> 16; }
     71 
     72     /** Return the next pseudo random number expressed as a signed SkFixed
     73         in the range (-SK_Fixed1..SK_Fixed1).
     74     */
     75     SkFixed nextSFixed1() { return this->nextS() >> 15; }
     76 
     77     /** Return the next pseudo random number expressed as a SkScalar
     78         in the range [0..SK_Scalar1).
     79     */
     80     SkScalar nextUScalar1() { return SkFixedToScalar(this->nextUFixed1()); }
     81 
     82     /** Return the next pseudo random number expressed as a SkScalar
     83         in the range (-SK_Scalar1..SK_Scalar1).
     84     */
     85     SkScalar nextSScalar1() { return SkFixedToScalar(this->nextSFixed1()); }
     86 
     87     /** Return the next pseudo random number as a signed 64bit value.
     88     */
     89     void next64(Sk64* a) {
     90         SkASSERT(a);
     91         a->set(this->nextS(), this->nextU());
     92     }
     93 
     94     /** Set the seed of the random object. The seed is initialized to 0 when the
     95         object is first created, and is updated each time the next pseudo random
     96         number is requested.
     97     */
     98     void setSeed(int32_t seed) { fSeed = (uint32_t)seed; }
     99 
    100 private:
    101     //  See "Numerical Recipes in C", 1992 page 284 for these constants
    102     enum {
    103         kMul = 1664525,
    104         kAdd = 1013904223
    105     };
    106     uint32_t fSeed;
    107 };
    108 
    109 #endif
    110 
    111