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//===-- runtime/random.cpp ------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
// Implements the intrinsic subroutines RANDOM_INIT, RANDOM_NUMBER, and
// RANDOM_SEED.
#include "flang/Runtime/random.h"
#include "lock.h"
#include "flang/Common/leading-zero-bit-count.h"
#include "flang/Common/uint128.h"
#include "flang/Runtime/cpp-type.h"
#include "flang/Runtime/descriptor.h"
#include <algorithm>
#include <cmath>
#include <cstdint>
#include <ctime>
#include <limits>
#include <memory>
#include <random>
namespace Fortran::runtime {
// Newer "Minimum standard", recommended by Park, Miller, and Stockmeyer in
// 1993. Same as C++17 std::minstd_rand, but explicitly instantiated for
// permanence.
using Generator =
std::linear_congruential_engine<std::uint_fast32_t, 48271, 0, 2147483647>;
using GeneratedWord = typename Generator::result_type;
static constexpr std::uint64_t range{
static_cast<std::uint64_t>(Generator::max() - Generator::min() + 1)};
static constexpr bool rangeIsPowerOfTwo{(range & (range - 1)) == 0};
static constexpr int rangeBits{
64 - common::LeadingZeroBitCount(range) - !rangeIsPowerOfTwo};
static Lock lock;
static Generator generator;
template <typename REAL, int PREC>
inline void Generate(const Descriptor &harvest) {
static constexpr std::size_t minBits{
std::max<std::size_t>(PREC, 8 * sizeof(GeneratedWord))};
using Int = common::HostUnsignedIntType<minBits>;
static constexpr std::size_t words{
static_cast<std::size_t>(PREC + rangeBits - 1) / rangeBits};
std::size_t elements{harvest.Elements()};
SubscriptValue at[maxRank];
harvest.GetLowerBounds(at);
{
CriticalSection critical{lock};
for (std::size_t j{0}; j < elements; ++j) {
Int fraction{generator()};
if constexpr (words > 1) {
for (std::size_t k{1}; k < words; ++k) {
static constexpr auto rangeMask{(GeneratedWord{1} << rangeBits) - 1};
GeneratedWord word{(generator() - generator.min()) & rangeMask};
fraction = (fraction << rangeBits) | word;
}
}
fraction >>= words * rangeBits - PREC;
*harvest.Element<REAL>(at) =
std::ldexp(static_cast<REAL>(fraction), -(PREC + 1));
harvest.IncrementSubscripts(at);
}
}
}
extern "C" {
void RTNAME(RandomInit)(bool repeatable, bool /*image_distinct*/) {
// TODO: multiple images and image_distinct: add image number
{
CriticalSection critical{lock};
if (repeatable) {
generator.seed(0);
} else {
generator.seed(std::time(nullptr));
}
}
}
void RTNAME(RandomNumber)(
const Descriptor &harvest, const char *source, int line) {
Terminator terminator{source, line};
auto typeCode{harvest.type().GetCategoryAndKind()};
RUNTIME_CHECK(terminator, typeCode && typeCode->first == TypeCategory::Real);
int kind{typeCode->second};
switch (kind) {
// TODO: REAL (2 & 3)
case 4:
Generate<CppTypeFor<TypeCategory::Real, 4>, 24>(harvest);
break;
case 8:
Generate<CppTypeFor<TypeCategory::Real, 8>, 53>(harvest);
break;
#if LONG_DOUBLE == 80
case 10:
Generate<CppTypeFor<TypeCategory::Real, 10>, 64>(harvest);
break;
#elif LONG_DOUBLE == 128
case 16:
Generate<CppTypeFor<TypeCategory::Real, 16>, 113>(harvest);
break;
#endif
default:
terminator.Crash("RANDOM_NUMBER(): unsupported REAL kind %d", kind);
}
}
void RTNAME(RandomSeedSize)(
const Descriptor &size, const char *source, int line) {
Terminator terminator{source, line};
auto typeCode{size.type().GetCategoryAndKind()};
RUNTIME_CHECK(terminator,
size.rank() == 0 && typeCode && typeCode->first == TypeCategory::Integer);
int kind{typeCode->second};
switch (kind) {
case 4:
*size.OffsetElement<CppTypeFor<TypeCategory::Integer, 4>>() = 1;
break;
case 8:
*size.OffsetElement<CppTypeFor<TypeCategory::Integer, 8>>() = 1;
break;
default:
terminator.Crash("RANDOM_SEED(SIZE=): bad kind %d\n", kind);
}
}
void RTNAME(RandomSeedPut)(
const Descriptor &put, const char *source, int line) {
Terminator terminator{source, line};
auto typeCode{put.type().GetCategoryAndKind()};
RUNTIME_CHECK(terminator,
put.rank() == 1 && typeCode && typeCode->first == TypeCategory::Integer &&
put.GetDimension(0).Extent() >= 1);
int kind{typeCode->second};
GeneratedWord seed;
switch (kind) {
case 4:
seed = *put.OffsetElement<CppTypeFor<TypeCategory::Integer, 4>>();
break;
case 8:
seed = *put.OffsetElement<CppTypeFor<TypeCategory::Integer, 8>>();
break;
default:
terminator.Crash("RANDOM_SEED(PUT=): bad kind %d\n", kind);
}
{
CriticalSection critical{lock};
generator.seed(seed);
}
}
void RTNAME(RandomSeedDefaultPut)() {
// TODO: should this be time &/or image dependent?
{
CriticalSection critical{lock};
generator.seed(0);
}
}
void RTNAME(RandomSeedGet)(
const Descriptor &got, const char *source, int line) {
Terminator terminator{source, line};
auto typeCode{got.type().GetCategoryAndKind()};
RUNTIME_CHECK(terminator,
got.rank() == 1 && typeCode && typeCode->first == TypeCategory::Integer &&
got.GetDimension(0).Extent() >= 1);
int kind{typeCode->second};
GeneratedWord seed;
{
CriticalSection critical{lock};
seed = generator();
generator.seed(seed);
}
switch (kind) {
case 4:
*got.OffsetElement<CppTypeFor<TypeCategory::Integer, 4>>() = seed;
break;
case 8:
*got.OffsetElement<CppTypeFor<TypeCategory::Integer, 8>>() = seed;
break;
default:
terminator.Crash("RANDOM_SEED(GET=): bad kind %d\n", kind);
}
}
} // extern "C"
} // namespace Fortran::runtime
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