src/base/random.cc

   1 /*
   2  * Copyright (c) 2003-2005 The Regents of The University of Michigan
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions are
   7  * met: redistributions of source code must retain the above copyright
   8  * notice, this list of conditions and the following disclaimer;
   9  * redistributions in binary form must reproduce the above copyright
  10  * notice, this list of conditions and the following disclaimer in the
  11  * documentation and/or other materials provided with the distribution;
  12  * neither the name of the copyright holders nor the names of its
  13  * contributors may be used to endorse or promote products derived from
  14  * this software without specific prior written permission.
  15  *
  16  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  17  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  18  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  19  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  20  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  21  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  22  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  26  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27  *
  28  * Authors: Nathan Binkert
  29  *          Ali Saidi
  30  */
  31
  32 #include <limits>
  33 #include "base/fenv.hh"
  34 #include "base/intmath.hh"
  35 #include "base/misc.hh"
  36 #include "base/random.hh"
  37 #include "sim/serialize.hh"
  38
  39 using namespace std;
  40
  41 Random::Random()
  42 {
  43     // default random seed taken from original source
  44     init(5489);
  45 }
  46
  47 Random::Random(uint32_t s)
  48 {
  49     init(s);
  50 }
  51
  52 Random::Random(uint32_t init_key[], int key_length)
  53 {
  54     init(init_key, key_length);
  55 }
  56
  57 Random::~Random()
  58 {
  59 }
  60
  61 // To preserve the uniform random distribution between min and max,
  62 // and allow all numbers to be represented, we generate a uniform
  63 // random number to the nearest power of two greater than max.  If
  64 // this number doesn't fall between 0 and max, we try again.  Anything
  65 // else would skew the distribution.
  66 uint32_t
  67 Random::genrand(uint32_t max)
  68 {
  69     if (max == 0)
  70         return 0;
  71     if (max == std::numeric_limits<uint32_t>::max())
  72         return genrand();
  73
  74     int log = ceilLog2(max + 1);
  75     int shift = (sizeof(uint32_t) * 8 - log);
  76     uint32_t random;
  77
  78     do {
  79         random = genrand() >> shift;
  80     } while (random > max);
  81
  82     return random;
  83 }
  84
  85 uint64_t
  86 Random::genrand(uint64_t max)
  87 {
  88     if (max == 0)
  89         return 0;
  90     if (max == std::numeric_limits<uint64_t>::max())
  91         return genrand();
  92
  93     int log = ceilLog2(max + 1);
  94     int shift = (sizeof(uint64_t) * 8 - log);
  95     uint64_t random;
  96
  97     do {
  98         random = (uint64_t)genrand() << 32 | (uint64_t)genrand();
  99         random = random >> shift;
 100     } while (random > max);
 101
 102     return random;
 103 }
 104
 105 void
 106 Random::serialize(const string &base, ostream &os)
 107 {
 108     int length = N;
 109     paramOut(os, base + ".mti", mti);
 110     paramOut(os, base + ".length", length);
 111     arrayParamOut(os, base + ".data", mt, length);
 112 }
 113
 114 void
 115 Random::unserialize(const string &base, Checkpoint *cp, const string &section)
 116 {
 117     int length;
 118
 119     paramIn(cp, section, base + ".mti", mti);
 120     paramIn(cp, section, base + ".length", length);
 121     if (length != N)
 122         panic("cant unserialize random number data. length != %d\n", length);
 123
 124     arrayParamIn(cp, section, base + ".data", mt, length);
 125 }
 126
 127 Random random_mt;