1 //===-- runtime/random.cpp ------------------------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 // Implements the intrinsic subroutines RANDOM_INIT, RANDOM_NUMBER, and
10 // RANDOM_SEED.
11 
12 #include "random.h"
13 #include "cpp-type.h"
14 #include "descriptor.h"
15 #include "lock.h"
16 #include "flang/Common/leading-zero-bit-count.h"
17 #include "flang/Common/uint128.h"
18 #include <algorithm>
19 #include <cmath>
20 #include <cstdint>
21 #include <ctime>
22 #include <limits>
23 #include <memory>
24 #include <random>
25 
26 namespace Fortran::runtime {
27 
28 // Newer "Minimum standard", recommended by Park, Miller, and Stockmeyer in
29 // 1993. Same as C++17 std::minstd_rand, but explicitly instantiated for
30 // permanence.
31 using Generator =
32     std::linear_congruential_engine<std::uint_fast32_t, 48271, 0, 2147483647>;
33 
34 using GeneratedWord = typename Generator::result_type;
35 static constexpr std::uint64_t range{
36     static_cast<std::uint64_t>(Generator::max() - Generator::min() + 1)};
37 static constexpr bool rangeIsPowerOfTwo{(range & (range - 1)) == 0};
38 static constexpr int rangeBits{
39     64 - common::LeadingZeroBitCount(range) - !rangeIsPowerOfTwo};
40 
41 static Lock lock;
42 static Generator generator;
43 
44 template <typename REAL, int PREC>
Generate(const Descriptor & harvest)45 inline void Generate(const Descriptor &harvest) {
46   static constexpr std::size_t minBits{
47       std::max<std::size_t>(PREC, 8 * sizeof(GeneratedWord))};
48   using Int = common::HostUnsignedIntType<minBits>;
49   static constexpr std::size_t words{
50       static_cast<std::size_t>(PREC + rangeBits - 1) / rangeBits};
51   std::size_t elements{harvest.Elements()};
52   SubscriptValue at[maxRank];
53   harvest.GetLowerBounds(at);
54   {
55     CriticalSection critical{lock};
56     for (std::size_t j{0}; j < elements; ++j) {
57       Int fraction{generator()};
58       if constexpr (words > 1) {
59         for (std::size_t k{1}; k < words; ++k) {
60           static constexpr auto rangeMask{(GeneratedWord{1} << rangeBits) - 1};
61           GeneratedWord word{(generator() - generator.min()) & rangeMask};
62           fraction = (fraction << rangeBits) | word;
63         }
64       }
65       fraction >>= words * rangeBits - PREC;
66       *harvest.Element<REAL>(at) =
67           std::ldexp(static_cast<REAL>(fraction), -(PREC + 1));
68       harvest.IncrementSubscripts(at);
69     }
70   }
71 }
72 
73 extern "C" {
74 
RTNAME(RandomInit)75 void RTNAME(RandomInit)(bool repeatable, bool /*image_distinct*/) {
76   // TODO: multiple images and image_distinct: add image number
77   {
78     CriticalSection critical{lock};
79     if (repeatable) {
80       generator.seed(0);
81     } else {
82       generator.seed(std::time(nullptr));
83     }
84   }
85 }
86 
RTNAME(RandomNumber)87 void RTNAME(RandomNumber)(
88     const Descriptor &harvest, const char *source, int line) {
89   Terminator terminator{source, line};
90   auto typeCode{harvest.type().GetCategoryAndKind()};
91   RUNTIME_CHECK(terminator, typeCode && typeCode->first == TypeCategory::Real);
92   int kind{typeCode->second};
93   switch (kind) {
94   // TODO: REAL (2 & 3)
95   case 4:
96     Generate<CppTypeFor<TypeCategory::Real, 4>, 24>(harvest);
97     break;
98   case 8:
99     Generate<CppTypeFor<TypeCategory::Real, 8>, 53>(harvest);
100     break;
101 #if LONG_DOUBLE == 80
102   case 10:
103     Generate<CppTypeFor<TypeCategory::Real, 10>, 64>(harvest);
104     break;
105 #elif LONG_DOUBLE == 128
106   case 16:
107     Generate<CppTypeFor<TypeCategory::Real, 16>, 113>(harvest);
108     break;
109 #endif
110   default:
111     terminator.Crash("RANDOM_NUMBER(): unsupported REAL kind %d", kind);
112   }
113 }
114 
RTNAME(RandomSeedSize)115 void RTNAME(RandomSeedSize)(
116     const Descriptor &size, const char *source, int line) {
117   Terminator terminator{source, line};
118   auto typeCode{size.type().GetCategoryAndKind()};
119   RUNTIME_CHECK(terminator,
120       size.rank() == 0 && typeCode && typeCode->first == TypeCategory::Integer);
121   int kind{typeCode->second};
122   switch (kind) {
123   case 4:
124     *size.OffsetElement<CppTypeFor<TypeCategory::Integer, 4>>() = 1;
125     break;
126   case 8:
127     *size.OffsetElement<CppTypeFor<TypeCategory::Integer, 8>>() = 1;
128     break;
129   default:
130     terminator.Crash("RANDOM_SEED(SIZE=): bad kind %d\n", kind);
131   }
132 }
133 
RTNAME(RandomSeedPut)134 void RTNAME(RandomSeedPut)(
135     const Descriptor &put, const char *source, int line) {
136   Terminator terminator{source, line};
137   auto typeCode{put.type().GetCategoryAndKind()};
138   RUNTIME_CHECK(terminator,
139       put.rank() == 1 && typeCode && typeCode->first == TypeCategory::Integer &&
140           put.GetDimension(0).Extent() >= 1);
141   int kind{typeCode->second};
142   GeneratedWord seed;
143   switch (kind) {
144   case 4:
145     seed = *put.OffsetElement<CppTypeFor<TypeCategory::Integer, 4>>();
146     break;
147   case 8:
148     seed = *put.OffsetElement<CppTypeFor<TypeCategory::Integer, 8>>();
149     break;
150   default:
151     terminator.Crash("RANDOM_SEED(PUT=): bad kind %d\n", kind);
152   }
153   {
154     CriticalSection critical{lock};
155     generator.seed(seed);
156   }
157 }
158 
RTNAME(RandomSeedDefaultPut)159 void RTNAME(RandomSeedDefaultPut)() {
160   // TODO: should this be time &/or image dependent?
161   {
162     CriticalSection critical{lock};
163     generator.seed(0);
164   }
165 }
166 
RTNAME(RandomSeedGet)167 void RTNAME(RandomSeedGet)(
168     const Descriptor &got, const char *source, int line) {
169   Terminator terminator{source, line};
170   auto typeCode{got.type().GetCategoryAndKind()};
171   RUNTIME_CHECK(terminator,
172       got.rank() == 1 && typeCode && typeCode->first == TypeCategory::Integer &&
173           got.GetDimension(0).Extent() >= 1);
174   int kind{typeCode->second};
175   GeneratedWord seed;
176   {
177     CriticalSection critical{lock};
178     seed = generator();
179     generator.seed(seed);
180   }
181   switch (kind) {
182   case 4:
183     *got.OffsetElement<CppTypeFor<TypeCategory::Integer, 4>>() = seed;
184     break;
185   case 8:
186     *got.OffsetElement<CppTypeFor<TypeCategory::Integer, 8>>() = seed;
187     break;
188   default:
189     terminator.Crash("RANDOM_SEED(GET=): bad kind %d\n", kind);
190   }
191 }
192 } // extern "C"
193 } // namespace Fortran::runtime
194