wtf/RandomNumber.cpp

   1 /*
   2  * Copyright (C) 2006, 2007, 2008 Apple Inc. All rights reserved.
   3  *           (C) 2008, 2009 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 "CryptographicallyRandomNumber.h"
  31 #include "RandomNumberSeed.h"
  32
  33 #include <limits>
  34 #include <limits.h>
  35 #include <stdint.h>
  36 #include <stdlib.h>
  37
  38 #if USE(MERSENNE_TWISTER_19937)
  39 extern "C" {
  40 #include "mt19937ar.c"
  41 }
  42 #endif
  43
  44 #if PLATFORM(BREWMP)
  45 #include <AEEAppGen.h>
  46 #include <AEESource.h>
  47 #include <AEEStdLib.h>
  48 #include <wtf/brew/RefPtrBrew.h>
  49 #include <wtf/brew/ShellBrew.h>
  50 #endif
  51
  52 namespace WTF {
  53
  54 double randomNumber()
  55 {
  56 #if USE(OS_RANDOMNESS)
  57     uint32_t bits = cryptographicallyRandomNumber();
  58     return static_cast<double>(bits) / (static_cast<double>(std::numeric_limits<uint32_t>::max()) + 1.0);
  59 #else
  60     // Without OS_RANDOMNESS, we fall back to other random number generators
  61     // that might not be cryptographically secure. Ideally, most ports would
  62     // define USE(OS_RANDOMNESS).
  63
  64 #if !ENABLE(WTF_MULTIPLE_THREADS)
  65     static bool s_initialized = false;
  66     if (!s_initialized) {
  67         initializeRandomNumberGenerator();
  68         s_initialized = true;
  69     }
  70 #endif
  71
  72 #if USE(MERSENNE_TWISTER_19937)
  73     return genrand_res53();
  74 #elif PLATFORM(BREWMP)
  75     uint32_t bits;
  76     // Is this a cryptographically strong source of random numbers? If so, we
  77     // should move this into OSRandomSource.
  78     // http://csrc.nist.gov/groups/STM/cmvp/documents/140-1/140sp/140sp851.pdf
  79     // is slightly unclear on this point, although it seems to imply that it is
  80     // secure.
  81     RefPtr<ISource> randomSource = createRefPtrInstance<ISource>(AEECLSID_RANDOM);
  82     ISOURCE_Read(randomSource.get(), reinterpret_cast<char*>(&bits), 4);
  83
  84     return static_cast<double>(bits) / (static_cast<double>(std::numeric_limits<uint32_t>::max()) + 1.0);
  85 #else
  86     uint32_t part1 = rand() & (RAND_MAX - 1);
  87     uint32_t part2 = rand() & (RAND_MAX - 1);
  88     // rand only provides 31 bits, and the low order bits of that aren't very random
  89     // so we take the high 26 bits of part 1, and the high 27 bits of part2.
  90     part1 >>= 5; // drop the low 5 bits
  91     part2 >>= 4; // drop the low 4 bits
  92     uint64_t fullRandom = part1;
  93     fullRandom <<= 27;
  94     fullRandom |= part2;
  95
  96     // Mask off the low 53bits
  97     fullRandom &= (1LL << 53) - 1;
  98     return static_cast<double>(fullRandom)/static_cast<double>(1LL << 53);
  99 #endif
 100 #endif
 101 }
 102
 103 }