Dogcows Code - chaz/yoink/blob - src/random.cc

   1
   2 /*******************************************************************************
   3
   4  Copyright (c) 2009, Charles McGarvey
   5  All rights reserved.
   6
   7  Redistribution   and   use  in  source  and  binary  forms,  with  or  without
   8  modification, are permitted provided that the following conditions are met:
   9
  10    * Redistributions  of  source  code  must retain the above copyright notice,
  11      this list of conditions and the following disclaimer.
  12    * Redistributions  in binary form must reproduce the above copyright notice,
  13      this  list of conditions and the following disclaimer in the documentation
  14      and/or other materials provided with the distribution.
  15
  16  THIS  SOFTWARE  IS  PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  17  AND  ANY  EXPRESS  OR  IMPLIED  WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  18  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  19  DISCLAIMED.  IN  NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
  20  FOR  ANY  DIRECT,  INDIRECT,  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  21  DAMAGES  (INCLUDING,  BUT  NOT  LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  22  SERVICES;  LOSS  OF  USE,  DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  23  CAUSED  AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  24  OR  TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  25  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  26
  27 *******************************************************************************/
  28
  29 #include <cstdlib>              // srand, rand, RAND_MAX
  30 #include <ctime>                // time
  31 #include <cmath>                // log
  32 #include <climits>              // ULONG_MAX
  33
  34 #include "random.hh"
  35
  36
  37 namespace rng {
  38
  39 unsigned seed(unsigned theSeed)
  40 {
  41         srand(theSeed);
  42         return theSeed;
  43 }
  44
  45 unsigned seed()
  46 {
  47         return seed(time(0));
  48 }
  49
  50
  51 template <typename T>
  52 T get()
  53 {
  54         const  float ln2 = 0.693147;
  55         static const unsigned bitsPerPiece = std::log(float(RAND_MAX)) / ln2;
  56         static const unsigned sizeOfType = sizeof(T) * 8;
  57         static const unsigned pieces = sizeOfType / bitsPerPiece +
  58                                                                  ((sizeOfType % bitsPerPiece) ? 1 : 0);
  59
  60         T bits = 0;
  61
  62         // we need to call rand() multiple times if it won't provide enough random
  63         // bits to fill the size of the given type
  64         for (unsigned i = 0; i < pieces; i++)
  65         {
  66                 long piece = rand();
  67                 bits |= piece << (i * bitsPerPiece);
  68         }
  69
  70         return bits;
  71 }
  72
  73
  74 template <>
  75 bool get<bool>()
  76 {
  77         return rand() % 2;
  78 }
  79
  80 template <typename T>
  81 T get(T lower, T upper)
  82 {
  83         unsigned short randInt = get<unsigned int>();
  84         return lower + T(randInt % (upper - lower + 1));
  85 }
  86
  87 template <>
  88 float get(float lower, float upper)
  89 {
  90         unsigned long randInt = get<unsigned long>();
  91         return (float(randInt) / float(ULONG_MAX)) * (upper - lower) + lower;
  92 }
  93
  94 template <>
  95 double get(double lower, double upper)
  96 {
  97         unsigned long long randInt = get<unsigned long long>();
  98         return (double(randInt) / double(ULLONG_MAX)) * (upper - lower) + lower;
  99 }
 100
 101 template <>
 102 float get()
 103 {
 104         return get<float>(0.0, 1.0);
 105 }
 106
 107 template <>
 108 double get()
 109 {
 110         return get<double>(0.0, 1.0);
 111 }
 112
 113
 114 }; // namespace rng
 115