QUIC - cleanup changes to sync chromium tree with internal source.
[chromium-blink-merge.git] / base / rand_util.cc
blob931eb4e943e646e2f39e2848b33683247b5b4725
1 // Copyright (c) 2011 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.
5 #include "base/rand_util.h"
7 #include <math.h>
8 #include <stdint.h>
10 #include <algorithm>
11 #include <limits>
13 #include "base/basictypes.h"
14 #include "base/logging.h"
15 #include "base/strings/string_util.h"
17 namespace base {
19 int RandInt(int min, int max) {
20 DCHECK_LE(min, max);
22 uint64 range = static_cast<uint64>(max) - min + 1;
23 int result = min + static_cast<int>(base::RandGenerator(range));
24 DCHECK_GE(result, min);
25 DCHECK_LE(result, max);
26 return result;
29 double RandDouble() {
30 return BitsToOpenEndedUnitInterval(base::RandUint64());
33 double BitsToOpenEndedUnitInterval(uint64 bits) {
34 // We try to get maximum precision by masking out as many bits as will fit
35 // in the target type's mantissa, and raising it to an appropriate power to
36 // produce output in the range [0, 1). For IEEE 754 doubles, the mantissa
37 // is expected to accommodate 53 bits.
39 COMPILE_ASSERT(std::numeric_limits<double>::radix == 2, otherwise_use_scalbn);
40 static const int kBits = std::numeric_limits<double>::digits;
41 uint64 random_bits = bits & ((UINT64_C(1) << kBits) - 1);
42 double result = ldexp(static_cast<double>(random_bits), -1 * kBits);
43 DCHECK_GE(result, 0.0);
44 DCHECK_LT(result, 1.0);
45 return result;
48 uint64 RandGenerator(uint64 range) {
49 DCHECK_GT(range, 0u);
50 // We must discard random results above this number, as they would
51 // make the random generator non-uniform (consider e.g. if
52 // MAX_UINT64 was 7 and |range| was 5, then a result of 1 would be twice
53 // as likely as a result of 3 or 4).
54 uint64 max_acceptable_value =
55 (std::numeric_limits<uint64>::max() / range) * range - 1;
57 uint64 value;
58 do {
59 value = base::RandUint64();
60 } while (value > max_acceptable_value);
62 return value % range;
65 std::string RandBytesAsString(size_t length) {
66 DCHECK_GT(length, 0u);
67 std::string result;
68 RandBytes(WriteInto(&result, length + 1), length);
69 return result;
72 } // namespace base