blob: 31e9dd1d286954e410a84781afae8b8754d0c30f (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
|
// Copyright (c) 2026 Progmasoft.
// SPDX-License-Identifier: MPL-2.0 WITH AdditionRef-Progmasoft-Exception-1.1
#pragma once
#include <Progmasoft/Catch3/Detail/InvalidArgument.hpp>
#include <Progmasoft/Catch3/Detail/TypeTraits.hpp>
#include <cstdint>
#include <limits>
#include <stdexcept>
#include <type_traits>
namespace Progmasoft::Catch3
{
/// Small, deterministic random source for repeatable property-test cases.
///
/// The SplitMix64 sequence is specified here instead of delegating to a
/// standard-library engine, whose output sequence is not portable between
/// library implementations. A Random object is intentionally not
/// thread-safe; property trials receive independent instances derived from
/// the root seed.
class Random final
{
public:
explicit constexpr Random(std::uint64_t seed) noexcept
: state_(seed)
{}
/// Returns the next value in the stable SplitMix64 sequence.
[[nodiscard]] constexpr std::uint64_t
Next() noexcept
{
state_ += kGamma;
std::uint64_t value = state_;
value = (value ^ (value >> 30U)) * kMultiplierOne;
value = (value ^ (value >> 27U)) * kMultiplierTwo;
return value ^ (value >> 31U);
}
/// Returns a value in [0, bound); bound == 0 requests the full uint64
/// range.
[[nodiscard]] constexpr std::uint64_t
Below(std::uint64_t bound) noexcept
{
if (bound == 0)
{
return Next();
}
// Rejection sampling avoids the modulo bias of a single `% bound`.
const std::uint64_t threshold
= (std::uint64_t{ 0 } - bound) % bound;
while (true)
{
const std::uint64_t value = Next();
if (value >= threshold)
{
return value % bound;
}
}
}
/// Returns an inclusive integral value without overflowing at type
/// limits.
template<typename IntegerType, Detail::EnableIfInteger<IntegerType> = 0>
[[nodiscard]] IntegerType
Between(IntegerType minimum, IntegerType maximum)
{
if (minimum > maximum)
{
Detail::RejectInvalidArgument(
"Random::Between requires minimum <= maximum");
}
using UnsignedType = std::make_unsigned_t<IntegerType>;
static_assert(std::numeric_limits<UnsignedType>::digits <= 64);
constexpr unsigned kBitCount = static_cast<unsigned>(
std::numeric_limits<UnsignedType>::digits);
constexpr UnsignedType kSignBit = UnsignedType{ 1 }
<< (kBitCount - 1U);
// Flipping the sign bit orders signed values as unsigned ones.
const UnsignedType flip
= std::is_signed_v<IntegerType> ? kSignBit : UnsignedType{};
const auto lower
= static_cast<UnsignedType>(static_cast<UnsignedType>(minimum)
^ flip);
const auto upper
= static_cast<UnsignedType>(static_cast<UnsignedType>(maximum)
^ flip);
// Unsigned wrap to zero represents the complete value domain.
const UnsignedType width
= static_cast<UnsignedType>(upper - lower + UnsignedType{ 1 });
const UnsignedType offset
= width == 0 ? static_cast<UnsignedType>(Next())
: static_cast<UnsignedType>(
Below(static_cast<std::uint64_t>(width)));
return static_cast<IntegerType>(
static_cast<UnsignedType>(lower + offset) ^ flip);
}
/// Derives an independent, reproducible seed for one trial.
[[nodiscard]] static constexpr std::uint64_t
DeriveSeed(std::uint64_t rootSeed, std::uint64_t trialIndex) noexcept
{
Random trialRandom(rootSeed + kGamma * (trialIndex + 1U));
return trialRandom.Next();
}
private:
static constexpr std::uint64_t kGamma = 0x9E3779B97F4A7C15ULL;
static constexpr std::uint64_t kMultiplierOne = 0xBF58476D1CE4E5B9ULL;
static constexpr std::uint64_t kMultiplierTwo = 0x94D049BB133111EBULL;
std::uint64_t state_;
};
} // namespace Progmasoft::Catch3
|