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https://github.com/mpusz/mp-units.git
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Mateusz Pusz
0eea272ece
- Add `comparable_in_wide_type` / `CommonlyComparableQuantities` concept and `compare_quantities` helper in `quantity.h` that widens int reps to `double_width_int_for_t<Rep>` (__int128 for int64) before scaling, preventing silent overflow in cross-unit `operator==` / `operator<=>` - Add `try_get_value<T>` to `unit_magnitude` returning `std::optional<T>` (nullopt on overflow) and refactor `get_value<T>` unsigned path to delegate to it; extract logic into free `try_accumulate_element<T,M>` helper taking M as NTTP so GCC 12 treats it as a constant expression - Wire `scaling_overflows_non_zero_values` in `value_cast.h` through `try_get_value` so extreme ratios (e.g. km³ vs pm³) no longer abort at compile time when evaluated inside `requires` - Add positive tests (lb vs kg, km vs mi) exercising the int64→int128 widening path in `yard_pound_test.cpp` - Add negative tests using `no_cross_unit_int_comparison` template wrapper (necessary for soft SFINAE failure on GCC) for cubic(km)/cubic(pm), Zm/am (linear, factor=10^39>2^127) and cubic(mi)/cubic(pm)
103 lines
5.2 KiB
C++
103 lines
5.2 KiB
C++
// The MIT License (MIT)
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//
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// Copyright (c) 2018 Mateusz Pusz
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//
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// Permission is hereby granted, free of charge, to any person obtaining a copy
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// of this software and associated documentation files (the "Software"), to deal
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// in the Software without restriction, including without limitation the rights
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// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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// copies of the Software, and to permit persons to whom the Software is
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// furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in all
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// copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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// SOFTWARE.
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#include <mp-units/systems/isq/mechanics.h>
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#include <mp-units/systems/isq/space_and_time.h>
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#include <mp-units/systems/si/constants.h>
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#include <mp-units/systems/si/unit_symbols.h>
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#include <mp-units/systems/si/units.h>
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#include <mp-units/systems/yard_pound.h>
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namespace {
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using namespace mp_units;
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using namespace mp_units::si::unit_symbols;
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using namespace mp_units::yard_pound;
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using namespace mp_units::yard_pound::unit_symbols;
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// Mass
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static_assert(47 * isq::mass[lb] < 47 * isq::mass[si::kilogram]);
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static_assert(1 * isq::mass[lb] == 16 * isq::mass[oz]);
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static_assert(1 * isq::mass[oz] == 16 * isq::mass[dr]);
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static_assert(7'000 * isq::mass[gr] == 1 * isq::mass[lb]);
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// Length
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// https://en.wikipedia.org/wiki/United_States_customary_units#Length
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static_assert(20 * isq::length[twip] == 1 * isq::length[p]);
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static_assert(1000 * isq::length[mil] == 1 * isq::length[in]);
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static_assert(72 * isq::length[p] == 1 * isq::length[in]);
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static_assert(1 * isq::length[P] == 12 * isq::length[p]);
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static_assert(1 * isq::length[in] == 6 * isq::length[P]);
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static_assert(1 * isq::length[ft] == 12 * isq::length[in]);
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static_assert(1 * isq::length[yd] == 3 * isq::length[ft]);
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static_assert(10'000 * isq::length[yd] == 9'144 * isq::length[si::metre]);
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static_assert(1 * isq::length[mi] == 5280 * isq::length[ft]);
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static_assert(1 * isq::length[mi] == 1760 * isq::length[yd]);
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static_assert(1 * isq::length[lea] == 15'840 * isq::length[ft]);
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static_assert(1 * isq::length[lea] == 5280 * isq::length[yd]);
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static_assert(1 * isq::length[ftm] == 2 * isq::length[yd]);
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// Nautical
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static_assert(1 * isq::length[nmi] == 1852 * isq::length[si::metre]);
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static_assert(1 * isq::speed[kn] == isq::length(1 * nmi) / isq::duration(1 * si::hour));
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// Force
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static_assert(1 * isq::force[pdl] == isq::mass(1 * lb) * isq::length(1 * ft) /
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(isq::duration(1 * si::second) * isq::duration(1 * si::second)));
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static_assert(1 * isq::force[lbf] == isq::mass(1 * lb) * (1 * si::standard_gravity));
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static_assert(1 * isq::force[kip] == 1000 * isq::force[lbf]);
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// Pressure
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static_assert(1 * isq::pressure[psi] == isq::force(1 * lbf) / isq::area(1 * square(inch)));
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// Power
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static_assert(1 * isq::power[hp] == isq::length(33'000 * ft) * isq::force(1 * lbf) / isq::duration(1 * si::minute));
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// Cross-unit integer comparisons: both operand values fit in int64, but both scaled intermediates
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// exceed INT64_MAX and require __int128 arithmetic (double_width_int_for_t<int64_t>) to compare
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// correctly — demonstrating the overflow-safe widening introduced for cross-unit comparisons.
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// lb vs kg: common unit is their magnitude-GCD (≈ 1.7×10⁻⁷ g), scale factors are huge.
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// 100'000'000'000'000 × factor_lb ≈ 4.54×10²¹ > INT64_MAX
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static_assert(100'000'000'000'000 * isq::mass[lb] == 45'359'237'000'000 * isq::mass[si::kilogram]);
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// mi vs km: common unit is 64 mm (GCD of 1'609'344 mm and 1'000'000 mm);
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// scale factors km→cu = 15'625, mi→cu = 25'146.
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// 590'295'810'380'364 × 15'625 ≈ 9.223×10¹⁸ > INT64_MAX
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// 366'792'811'468'750 × 25'146 ≈ 9.223×10¹⁸ > INT64_MAX
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static_assert(590'295'810'380'364LL * isq::length[km] == 366'792'811'468'750LL * isq::length[mi]);
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static_assert(590'295'810'380'364LL * isq::length[km] > 366'792'811'468'749LL * isq::length[mi]);
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static_assert(590'295'810'380'364LL * isq::length[km] < 366'792'811'468'751LL * isq::length[mi]);
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// Comparisons disabled at compile-time when unit-ratio scaling would overflow even __int128.
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// A template wrapper is used so that SFINAE failure inside requires is a soft error, not a
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// hard error on GCC.
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template<Reference auto R1, Reference auto R2>
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constexpr bool no_cross_unit_int_comparison = !requires { 1 * R1 == 1 * R2; } && !requires { 1 * R1 < 1 * R2; } &&
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!requires { 1 * R2 == 1 * R1; } && !requires { 1 * R2 < 1 * R1; };
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// cubic(mi) vs cubic(pm): factor = (1.609344×10^15)^3 ≈ 4.17×10^45 > 2^127,
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// so even value=1 makes integer comparison ill-formed.
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static_assert(no_cross_unit_int_comparison<isq::volume[cubic(mi)], isq::volume[cubic(pm)]>);
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} // namespace
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