rand_util.cc revision c7f5f8508d98d5952d42ed7648c2a8f30a4da156 
1// Copyright (c) 2008 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<int64>(max) - min + 1;
20  uint64 number = base::RandUint64();
21  int result = min + static_cast<int>(number % range);
22  DCHECK(result >= min && result <= max);
23  return result;
24}
25
26double RandDouble() {
27  // We try to get maximum precision by masking out as many bits as will fit
28  // in the target type's mantissa, and raising it to an appropriate power to
29  // produce output in the range [0, 1).  For IEEE 754 doubles, the mantissa
30  // is expected to accommodate 53 bits.
31
32  COMPILE_ASSERT(std::numeric_limits<double>::radix == 2, otherwise_use_scalbn);
33  static const int kBits = std::numeric_limits<double>::digits;
34  uint64 random_bits = base::RandUint64() & ((GG_UINT64_C(1) << kBits) - 1);
35  double result = ldexp(static_cast<double>(random_bits), -1 * kBits);
36  DCHECK(result >= 0.0 && result < 1.0);
37  return result;
38}
39
40}  // namespace base
41