rand_util.cc revision 3345a6884c488ff3a535c2c9acdd33d74b37e311 
1// Copyright (c) 2010 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#include "base/rand_util.h"
6
7#include <math.h>
8
9#include <limits>
10
11#include "base/basictypes.h"
12#include "base/logging.h"
13
14namespace base {
15
16int RandInt(int min, int max) {
17  DCHECK(min <= max);
18
19  uint64 range = static_cast<uint64>(max) - min + 1;
20  int result = min + static_cast<int>(base::RandGenerator(range));
21  DCHECK(result >= min && result <= max);
22  return result;
23}
24
25double RandDouble() {
26  // We try to get maximum precision by masking out as many bits as will fit
27  // in the target type's mantissa, and raising it to an appropriate power to
28  // produce output in the range [0, 1).  For IEEE 754 doubles, the mantissa
29  // is expected to accommodate 53 bits.
30
31  COMPILE_ASSERT(std::numeric_limits<double>::radix == 2, otherwise_use_scalbn);
32  static const int kBits = std::numeric_limits<double>::digits;
33  uint64 random_bits = base::RandUint64() & ((GG_UINT64_C(1) << kBits) - 1);
34  double result = ldexp(static_cast<double>(random_bits), -1 * kBits);
35  DCHECK(result >= 0.0 && result < 1.0);
36  return result;
37}
38
39uint64 RandGenerator(uint64 max) {
40  DCHECK(max > 0);
41  return base::RandUint64() % max;
42}
43
44}  // namespace base
45