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Implement LWG-3809 Is subtract_with_carry_engine<uint16_t> supposed to work? #4194

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Merged
Stephan T. Lavavej (StephanTLavavej) merged 3 commits into from
Nov 17, 2023
Merged

Implement LWG-3809 Is subtract_with_carry_engine<uint16_t> supposed to work? #4194

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47044a5
Implement LWG-3809 Is `subtract_with_carry_engine<uint16_t>`...
frederick-vs-ja Nov 14, 2023
632084b
Fix narrowing conversion
frederick-vs-ja Nov 14, 2023
1e023af
Change `default_seed` usage to `0u` in more places.
StephanTLavavej Nov 15, 2023
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24 changes: 13 additions & 11 deletions stl/inc/random
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Original file line number Diff line number Diff line change
Expand Up @@ -677,9 +677,9 @@ public:
using _Mybase = _Circ_buf<_Ty, _Rx>;
using _Seed_t = typename _Swc_Traits::_Seed_t;

static constexpr size_t short_lag = _Sx;
static constexpr size_t long_lag = _Rx;
static constexpr _Seed_t default_seed = static_cast<_Seed_t>(19780503U);
static constexpr size_t short_lag = _Sx;
static constexpr size_t long_lag = _Rx;
static constexpr uint_least32_t default_seed = 19780503u;

_Swc_base() {
seed();
Expand All @@ -694,8 +694,9 @@ public:
seed(_Gx);
}

void seed(_Seed_t _Value = default_seed, bool _Readcy = false) { // set initial values from specified seed value
linear_congruential<_Seed_t, 40014U, 0U, 2147483563U> _Lc{_Value == 0U ? default_seed : _Value};
void seed(_Seed_t _Value = 0u, bool _Readcy = false) { // set initial values from specified seed value
linear_congruential_engine<uint_least32_t, 40014U, 0U, 2147483563U> _Lc{
static_cast<uint_least32_t>(_Value == 0U ? default_seed : _Value)};
Comment on lines +697 to +699

@jovibor jovibor Nov 15, 2023

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Style:
Case inconsistency between u and U literals, or it doesn't matter?

@frederick-vs-ja A. Jiang (frederick-vs-ja) Nov 16, 2023

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It seems that the standard wording consistently uses lowercase (u) in [rand], while MSVC STL consistently uses uppercase (U)...

_Reset(_Lc, _Readcy);
}

Expand Down Expand Up @@ -805,7 +806,7 @@ struct _Swc_traits { // traits for subtract_with_carry generator

static constexpr _Cy_t _Cy = 1;
static constexpr _Mod_t _Mod = _Mx;
static constexpr _Ty _Max = _Mx - 1;
static constexpr _Ty _Max = static_cast<_Ty>(_Mx - 1);

static int _Get_wc() noexcept { // compute number of 32-bit words per element
int _Kx;
Expand Down Expand Up @@ -892,7 +893,7 @@ public:

using _Mybase::default_seed;

subtract_with_carry() : _Mybase(default_seed) {}
subtract_with_carry() : _Mybase(0u) {}

explicit subtract_with_carry(_Ty _Xx0) : _Mybase(_Xx0) {}

Expand All @@ -901,15 +902,16 @@ public:
};
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_EXPORT_STD template <class _Ty, size_t _Wx, size_t _Sx, size_t _Rx>
class subtract_with_carry_engine : public subtract_with_carry<_Ty, (_Ty{1} << (_Wx - 1)) << 1, _Sx, _Rx> {
class subtract_with_carry_engine
: public subtract_with_carry<_Ty, static_cast<_Ty>((_Ty{1} << (_Wx - 1)) << 1), _Sx, _Rx> {
// subtract_with_carry generator
public:
_RNG_REQUIRE_UINTTYPE(subtract_with_carry_engine, _Ty);

static_assert(0U < _Sx && _Sx < _Rx && 0 < _Wx && _Wx <= numeric_limits<_Ty>::digits,
"invalid template argument for subtract_with_carry_engine");

static constexpr _Ty _Mx = (_Ty{1} << (_Wx - 1)) << 1;
static constexpr _Ty _Mx = static_cast<_Ty>((_Ty{1} << (_Wx - 1)) << 1);
static constexpr size_t word_size = _Wx;
static constexpr size_t short_lag = _Sx;
static constexpr size_t long_lag = _Rx;
Expand All @@ -920,7 +922,7 @@ public:

using _Mybase::default_seed;

subtract_with_carry_engine() : _Mybase(default_seed) {}
subtract_with_carry_engine() : _Mybase(0u) {}

explicit subtract_with_carry_engine(_Ty _Xx0) : _Mybase(_Xx0) {}

Expand All @@ -929,7 +931,7 @@ public:
seed(_Seq);
}

void seed(_Ty _Value = default_seed) { // set initial values from specified seed value
void seed(_Ty _Value = 0u) { // set initial values from specified seed value
_Mybase::seed(_Value);
}

Expand Down
29 changes: 22 additions & 7 deletions tests/std/tests/Dev11_0577418_random_seed_0/test.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,11 @@
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

#include <cassert>
#include <cstdint>
#include <random>
#include <type_traits>

#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)

using namespace std;

Expand All @@ -13,20 +17,31 @@ typename Engine::result_type run_10k(Engine engine) {
}

int main() {
assert(run_10k(minstd_rand0()) == 1043618065UL); // N3485 26.5.5 [rand.predef]/1
assert(run_10k(mt19937()) == 4123659995UL); // N3485 26.5.5 [rand.predef]/3
assert(run_10k(ranlux24_base()) == 7937952UL); // N3485 26.5.5 [rand.predef]/5
assert(run_10k(minstd_rand0()) == 1043618065UL); // N4964 [rand.predef]/1
assert(run_10k(mt19937()) == 4123659995UL); // N4964 [rand.predef]/3
assert(run_10k(ranlux24_base()) == 7937952UL); // N4964 [rand.predef]/5

// Also test VSO-214595 "subtract_with_carry_engine::seed should accept result_type"
subtract_with_carry_engine<unsigned long long, 64, 10, 24> ull_swc;
ull_swc.seed(0x12341234'00000000ULL);
assert(run_10k(ull_swc) == 0x01316AEA'3646F686ULL); // libstdc++ and libc++ agree (boost 1.60.0 disagrees)
assert(run_10k(ull_swc) == 0x1DD6C263'C41EEED0ULL); // value changed by LWG-3809

assert(minstd_rand0(0) == minstd_rand0()); // N3485 26.5.3.1 [rand.eng.lcong]/5
assert(mt19937(0) != mt19937()); // N3485 26.5.3.2 [rand.eng.mers]/6
assert(ranlux24_base(0) == ranlux24_base()); // N3485 26.5.3.3 [rand.eng.sub]/7
assert(minstd_rand0(0) == minstd_rand0()); // N4964 [rand.eng.lcong]/5
assert(mt19937(0) != mt19937()); // N4964 [rand.eng.mers]/6
assert(ranlux24_base(0) == ranlux24_base()); // N4964 [rand.eng.sub]/7

assert(run_10k(minstd_rand0(0)) == 1043618065UL); // QED
assert(run_10k(mt19937(0)) == 1543171712UL); // Boost 1.52.0 agrees
assert(run_10k(ranlux24_base(0)) == 7937952UL); // QED

// Also test LWG-3809 Is std::subtract_with_carry_engine<uint16_t> supposed to work?
STATIC_ASSERT(is_same_v<decltype(subtract_with_carry_engine<unsigned short, 16, 10, 24>::default_seed),
const uint_least32_t>);
STATIC_ASSERT(
is_same_v<decltype(subtract_with_carry_engine<unsigned int, 32, 10, 24>::default_seed), const uint_least32_t>);
STATIC_ASSERT(
is_same_v<decltype(subtract_with_carry_engine<unsigned long, 32, 10, 24>::default_seed), const uint_least32_t>);
STATIC_ASSERT(is_same_v<decltype(subtract_with_carry_engine<unsigned long long, 64, 10, 24>::default_seed),
const uint_least32_t>);
assert(run_10k(subtract_with_carry_engine<unsigned long long, 64, 10, 24>{}) == 6793538734622947770ULL);
}