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
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
|
// Copyright 2017 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#ifndef ABSL_RANDOM_INTERNAL_SALTED_SEED_SEQ_H_
#define ABSL_RANDOM_INTERNAL_SALTED_SEED_SEQ_H_
#include <cstdint>
#include <cstdlib>
#include <initializer_list>
#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>
#include <vector>
#include "absl/container/inlined_vector.h"
#include "absl/meta/type_traits.h"
#include "absl/random/internal/seed_material.h"
#include "absl/types/optional.h"
#include "absl/types/span.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace random_internal {
// This class conforms to the C++ Standard "Seed Sequence" concept
// [rand.req.seedseq].
//
// A `SaltedSeedSeq` is meant to wrap an existing seed sequence and modify
// generated sequence by mixing with extra entropy. This entropy may be
// build-dependent or process-dependent. The implementation may change to be
// have either or both kinds of entropy. If salt is not available sequence is
// not modified.
template <typename SSeq>
class SaltedSeedSeq {
public:
using inner_sequence_type = SSeq;
using result_type = typename SSeq::result_type;
SaltedSeedSeq() : seq_(absl::make_unique<SSeq>()) {}
template <typename Iterator>
SaltedSeedSeq(Iterator begin, Iterator end)
: seq_(absl::make_unique<SSeq>(begin, end)) {}
template <typename T>
SaltedSeedSeq(std::initializer_list<T> il)
: SaltedSeedSeq(il.begin(), il.end()) {}
SaltedSeedSeq(const SaltedSeedSeq&) = delete;
SaltedSeedSeq& operator=(const SaltedSeedSeq&) = delete;
SaltedSeedSeq(SaltedSeedSeq&&) = default;
SaltedSeedSeq& operator=(SaltedSeedSeq&&) = default;
template <typename RandomAccessIterator>
void generate(RandomAccessIterator begin, RandomAccessIterator end) {
using U = typename std::iterator_traits<RandomAccessIterator>::value_type;
// The common case is that generate is called with ContiguousIterators
// to uint arrays. Such contiguous memory regions may be optimized,
// which we detect here.
using TagType = absl::conditional_t<
(std::is_same<U, uint32_t>::value &&
(std::is_pointer<RandomAccessIterator>::value ||
std::is_same<RandomAccessIterator,
typename std::vector<U>::iterator>::value)),
ContiguousAndUint32Tag, DefaultTag>;
if (begin != end) {
generate_impl(TagType{}, begin, end, std::distance(begin, end));
}
}
template <typename OutIterator>
void param(OutIterator out) const {
seq_->param(out);
}
size_t size() const { return seq_->size(); }
private:
struct ContiguousAndUint32Tag {};
struct DefaultTag {};
// Generate which requires the iterators are contiguous pointers to uint32_t.
// Fills the initial seed buffer the underlying SSeq::generate() call,
// then mixes in the salt material.
template <typename Contiguous>
void generate_impl(ContiguousAndUint32Tag, Contiguous begin, Contiguous end,
size_t n) {
seq_->generate(begin, end);
const uint32_t salt = absl::random_internal::GetSaltMaterial().value_or(0);
auto span = absl::Span<uint32_t>(&*begin, n);
MixIntoSeedMaterial(absl::MakeConstSpan(&salt, 1), span);
}
// The uncommon case for generate is that it is called with iterators over
// some other buffer type which is assignable from a 32-bit value. In this
// case we allocate a temporary 32-bit buffer and then copy-assign back
// to the initial inputs.
template <typename RandomAccessIterator>
void generate_impl(DefaultTag, RandomAccessIterator begin,
RandomAccessIterator, size_t n) {
// Allocates a seed buffer of `n` elements, generates the seed, then
// copies the result into the `out` iterator.
absl::InlinedVector<uint32_t, 8> data(n, 0);
generate_impl(ContiguousAndUint32Tag{}, data.begin(), data.end(), n);
std::copy(data.begin(), data.end(), begin);
}
// Because [rand.req.seedseq] is not required to be copy-constructible,
// copy-assignable nor movable, we wrap it with unique pointer to be able
// to move SaltedSeedSeq.
std::unique_ptr<SSeq> seq_;
};
// is_salted_seed_seq indicates whether the type is a SaltedSeedSeq.
template <typename T, typename = void>
struct is_salted_seed_seq : public std::false_type {};
template <typename T>
struct is_salted_seed_seq<
T, typename std::enable_if<std::is_same<
T, SaltedSeedSeq<typename T::inner_sequence_type>>::value>::type>
: public std::true_type {};
// MakeSaltedSeedSeq returns a salted variant of the seed sequence.
// When provided with an existing SaltedSeedSeq, returns the input parameter,
// otherwise constructs a new SaltedSeedSeq which embodies the original
// non-salted seed parameters.
template <
typename SSeq, //
typename EnableIf = absl::enable_if_t<is_salted_seed_seq<SSeq>::value>>
SSeq MakeSaltedSeedSeq(SSeq&& seq) {
return SSeq(std::forward<SSeq>(seq));
}
template <
typename SSeq, //
typename EnableIf = absl::enable_if_t<!is_salted_seed_seq<SSeq>::value>>
SaltedSeedSeq<typename std::decay<SSeq>::type> MakeSaltedSeedSeq(SSeq&& seq) {
using sseq_type = typename std::decay<SSeq>::type;
using result_type = typename sseq_type::result_type;
absl::InlinedVector<result_type, 8> data;
seq.param(std::back_inserter(data));
return SaltedSeedSeq<sseq_type>(data.begin(), data.end());
}
} // namespace random_internal
ABSL_NAMESPACE_END
} // namespace absl
#endif // ABSL_RANDOM_INTERNAL_SALTED_SEED_SEQ_H_
|
