1 // Copyright 2018 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 #ifndef QUICHE_HTTP2_TEST_TOOLS_HTTP2_RANDOM_H_
6 #define QUICHE_HTTP2_TEST_TOOLS_HTTP2_RANDOM_H_
7 
8 #include <cmath>
9 #include <cstdint>
10 #include <limits>
11 #include <random>
12 #include <string>
13 
14 #include "absl/strings/string_view.h"
15 
16 namespace http2 {
17 namespace test {
18 
19 // The random number generator used for unit tests.  Since the algorithm is
20 // deterministic and fixed, this can be used to reproduce flakes in the unit
21 // tests caused by specific random values.
22 class Http2Random {
23  public:
24   Http2Random();
25 
26   Http2Random(const Http2Random&) = delete;
27   Http2Random& operator=(const Http2Random&) = delete;
28 
29   // Reproducible random number generation: by using the same key, the same
30   // sequence of results is obtained.
31   explicit Http2Random(absl::string_view key);
32   std::string Key() const;
33 
34   void FillRandom(void* buffer, size_t buffer_size);
35   std::string RandString(int length);
36 
37   // Returns a random 64-bit value.
38   uint64_t Rand64();
39 
40   // Return a uniformly distrubted random number in [0, n).
Uniform(uint32_t n)41   uint32_t Uniform(uint32_t n) { return Rand64() % n; }
42   // Return a uniformly distrubted random number in [lo, hi).
UniformInRange(uint64_t lo,uint64_t hi)43   uint64_t UniformInRange(uint64_t lo, uint64_t hi) {
44     return lo + Rand64() % (hi - lo);
45   }
46   // Return an integer of logarithmically random scale.
Skewed(uint32_t max_log)47   uint32_t Skewed(uint32_t max_log) {
48     const uint32_t base = Rand32() % (max_log + 1);
49     const uint32_t mask = ((base < 32) ? (1u << base) : 0u) - 1u;
50     return Rand32() & mask;
51   }
52   // Return a random number in [0, max] range that skews low.
RandomSizeSkewedLow(uint64_t max)53   uint64_t RandomSizeSkewedLow(uint64_t max) {
54     return std::round(max * std::pow(RandDouble(), 2));
55   }
56 
57   // Returns a random double between 0 and 1.
58   double RandDouble();
RandFloat()59   float RandFloat() { return RandDouble(); }
60 
61   // Has 1/n chance of returning true.
OneIn(int n)62   bool OneIn(int n) { return Uniform(n) == 0; }
63 
Rand8()64   uint8_t Rand8() { return Rand64(); }
Rand16()65   uint16_t Rand16() { return Rand64(); }
Rand32()66   uint32_t Rand32() { return Rand64(); }
67 
68   // Return a random string consisting of the characters from the specified
69   // alphabet.
70   std::string RandStringWithAlphabet(int length, absl::string_view alphabet);
71 
72   // STL UniformRandomNumberGenerator implementation.
73   using result_type = uint64_t;
min()74   static constexpr result_type min() { return 0; }
max()75   static constexpr result_type max() {
76     return std::numeric_limits<result_type>::max();
77   }
operator()78   result_type operator()() { return Rand64(); }
79 
80  private:
81   uint8_t key_[32];
82   uint32_t counter_ = 0;
83 };
84 
85 }  // namespace test
86 }  // namespace http2
87 
88 #endif  // QUICHE_HTTP2_TEST_TOOLS_HTTP2_RANDOM_H_
89