wtf/RandomNumber.cpp

   1 /*
   2  * Copyright (C) 2006, 2007, 2008 Apple Inc. All rights reserved.
   3  *           (C) 2008 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
  15  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  17  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
  18  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  19  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  20  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  21  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  22  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  23  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  24  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  25  */
  26
  27 #include "config.h"
  28 #include "RandomNumber.h"
  29
  30 #include "RandomNumberSeed.h"
  31
  32 #include <limits>
  33 #include <limits.h>
  34 #include <stdint.h>
  35 #include <stdlib.h>
  36
  37 namespace WTF {
  38
  39 double weakRandomNumber()
  40 {
  41 #if COMPILER(MSVC) && defined(_CRT_RAND_S)
  42     // rand_s is incredibly slow on windows so we fall back on rand for Math.random
  43     return (rand() + (rand() / (RAND_MAX + 1.0))) / (RAND_MAX + 1.0);
  44 #else
  45     return randomNumber();
  46 #endif
  47 }
  48
  49 double randomNumber()
  50 {
  51 #if !ENABLE(JSC_MULTIPLE_THREADS)
  52     static bool s_initialized = false;
  53     if (!s_initialized) {
  54         initializeRandomNumberGenerator();
  55         s_initialized = true;
  56     }
  57 #endif
  58
  59 #if COMPILER(MSVC) && defined(_CRT_RAND_S)
  60     uint32_t bits;
  61     rand_s(&bits);
  62     return static_cast<double>(bits) / (static_cast<double>(std::numeric_limits<uint32_t>::max()) + 1.0);
  63 #elif PLATFORM(DARWIN)
  64     uint32_t bits = arc4random();
  65     return static_cast<double>(bits) / (static_cast<double>(std::numeric_limits<uint32_t>::max()) + 1.0);
  66 #elif PLATFORM(UNIX)
  67     uint32_t part1 = random() & (RAND_MAX - 1);
  68     uint32_t part2 = random() & (RAND_MAX - 1);
  69     // random only provides 31 bits
  70     uint64_t fullRandom = part1;
  71     fullRandom <<= 31;
  72     fullRandom |= part2;
  73
  74     // Mask off the low 53bits
  75     fullRandom &= (1LL << 53) - 1;
  76     return static_cast<double>(fullRandom)/static_cast<double>(1LL << 53);
  77 #else
  78     uint32_t part1 = rand() & (RAND_MAX - 1);
  79     uint32_t part2 = rand() & (RAND_MAX - 1);
  80     // rand only provides 31 bits, and the low order bits of that aren't very random
  81     // so we take the high 26 bits of part 1, and the high 27 bits of part2.
  82     part1 >>= 5; // drop the low 5 bits
  83     part2 >>= 4; // drop the low 4 bits
  84     uint64_t fullRandom = part1;
  85     fullRandom <<= 27;
  86     fullRandom |= part2;
  87
  88     // Mask off the low 53bits
  89     fullRandom &= (1LL << 53) - 1;
  90     return static_cast<double>(fullRandom)/static_cast<double>(1LL << 53);
  91 #endif
  92 }
  93
  94 }