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Mateusz Pusz
efbc844199
* Fix #580: use fixed-point arithmetic for integer unit conversions Introduce a fixed-point implementation for unit conversions involving integer representations, avoiding loss of significant digits that previously occurred when the conversion factor was not a whole number. New files: - src/core/include/mp-units/bits/fixed_point.h: double_width_int<T> and fixed_point<T,n> types for exact rational scaling of integer values. Uses __int128 when available (__SIZEOF_INT128__) for 64-bit integers. - src/core/include/mp-units/framework/scaling.h: public scaling_traits<> customization point and scale<To>(M, value) free function. Provides built-in specializations for floating-point and integer-like types. - test/static/fixed_point_test.cpp: static assertions for the new types. - test/runtime/fixed_point_test.cpp: runtime arithmetic edge-case tests. Modified: - sudo_cast.h: replace hand-rolled conversion_value_traits / sudo_cast_value machinery with a single scale<To::rep>(c_mag, ...) call. - representation_concepts.h: add MagnitudeScalable concept; replace ComplexScalar with HasComplexOperations (which is its definition). - customization_points.h: add unspecified_rep tag and declare the primary scaling_traits<> template. - framework.h / CMakeLists.txt: wire in the new headers. - hacks.h: add MP_UNITS_DIAGNOSTIC_IGNORE_PEDANTIC and MP_UNITS_DIAGNOSTIC_IGNORE_SIGN_CONVERSION macros. - example/measurement.cpp: add scaling_traits specializations for measurement<T> to demonstrate the customization point. - test/static/{international,usc}_test.cpp: disable two tests that are blocked on issue #614. Co-authored-by: Tobias Hanhart <burnpanck@users.noreply.github.com> * Fix value_Type typo in floating_point_scaling_factor_type specialization The partial specialization for types with a nested value_type used 'value_Type' (capital T) instead of 'value_type', making the entire specialization dead code as the requires-clause could never be satisfied. Also fix 'mantiassa' -> 'mantissa' in the adjacent comment. * Fix docstring typos in scaling_traits documentation - 'quantitiy' -> 'quantity' - 'dictatet' -> 'dictated' - 'convetrible' -> 'convertible' - 'implemenation' -> 'implementation' - 'availabe' -> 'available' * Fix conflict resolution error: keep ComplexScalar name from master When resolving the merge conflict in representation_concepts.h, the PR's renamed version of the concept ('HasComplexOperations') was used instead of master's established name ('ComplexScalar'). The two concepts are semantically equivalent — burnpanck simply renamed it in his branch. Revert to the canonical 'ComplexScalar' name while retaining the new 'MagnitudeScalable' concept which was the actual addition from the PR. * Fix measurement.cpp: remove duplicate class definition from merge The PR branched from a version where measurement<T> was defined inline in measurement.cpp. Master later moved the class to example/include/ measurement.h and changed measurement.cpp to #include that header. The squash merge therefore introduced a duplicate definition: the class from the header and the PR's inline class were both visible, causing an 'ambiguous reference' error. Remove the now-redundant inline class; the scaling_traits specializations added by the PR work correctly with the class from measurement.h. * style: pre-commit * docs: chapters anchors improved in the "custom representation" chapter * docs: value conversions chapter improved * refactor: scaling support refactored * fix: clang-16 crash fixed * docs: `measurement` example documentation updated to match changes * fix: use exact wide-integer arithmetic for rational unit conversions on all platforms On ARM / Apple Silicon, long double == double (64-bit mantissa). The old fixed_point<T>(long double) initialiser lost ~12 bits of precision for 64-bit integer types when representing the scaling ratio, producing an error of ~49 units for the 10/9 (degree → gradian) conversion with a 10^18 input value. Fix by splitting the integer-path else-branch into two cases: • Pure rational M (is_integral(M * (denominator(M) / numerator(M))) == true): use (value * numerator) / denominator via double_width_int_for_t<> arithmetic. This is exact on every platform regardless of long double width. • Irrational M (involves π etc.): keep the long double fixed_point approximation. These conversions are inherently approximate; small values still produce correct truncated results on all platforms. Update the test comment to reflect the new exact-arithmetic path. Fixes CI failures on clang-18/ARM and apple-clang-16. * fix: replace floating-point TeX-point test with exact integer equivalent 72.27 is not exactly representable as double (it rounds to 72.2699...96). Multiplying by the conversion factor 100/7227 via long double gives a result ≥ 1.0 on x86 (80-bit long double, 64-bit mantissa) only by chance, but 0.99999...978 on ARM / Apple Silicon where long double == double (52-bit). The correct mathematical statement is: 7227 tex_point = 100 inch (exact rational relationship). Use that integer form instead of the inexact 72.27 double literal so the test is correct and platform-independent. --------- Co-authored-by: Tobias Hanhart <burnpanck@users.noreply.github.com>
98 lines
4.4 KiB
C++
98 lines
4.4 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/bits/fixed_point.h>
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#include <mp-units/compat_macros.h>
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#include <mp-units/framework.h>
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#include <mp-units/systems/angular.h>
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#ifdef MP_UNITS_IMPORT_STD
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import std;
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#else
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#include <cstdint>
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#include <type_traits>
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#endif
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using namespace mp_units;
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namespace {
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static_assert(std::is_same_v<detail::min_width_uint_t<1>, std::uint8_t>);
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static_assert(std::is_same_v<detail::min_width_uint_t<7>, std::uint8_t>);
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static_assert(std::is_same_v<detail::min_width_uint_t<8>, std::uint8_t>);
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static_assert(std::is_same_v<detail::min_width_uint_t<9>, std::uint16_t>);
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static_assert(std::is_same_v<detail::min_width_uint_t<31>, std::uint32_t>);
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static_assert(std::is_same_v<detail::min_width_uint_t<32>, std::uint32_t>);
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static_assert(std::is_same_v<detail::min_width_uint_t<33>, std::uint64_t>);
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using i128 = detail::double_width_int<std::int64_t>;
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using u128 = detail::double_width_int<std::uint64_t>;
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static_assert((((83 * 79 * 73) * (i128{97} << 64u) / 89) >> 64u) == (83 * 79 * 73 * 97) / 89);
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// scale<To>(M{}, value) — integer-to-integer path (exact arithmetic, no floating point)
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// scale(M{}, value) — floating-point same-type shorthand (To = From, uses value_type_t<From>)
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// integral factor: exact integer multiply
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static_assert(scale<int>(mag<1000>, 5) == 5000);
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static_assert(scale<long>(mag<60>, 2l) == 120l);
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// integral inverse: exact integer divide
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static_assert(scale<int>(mag_ratio<1, 1000>, 5000) == 5);
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static_assert(scale<int>(mag_ratio<1, 60>, 120) == 2);
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// rational M (3/2 * 4 == 6): exact double-width integer arithmetic
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static_assert(scale<int>(mag_ratio<3, 2>, 4) == 6);
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// (1/3 * 9 == 3)
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static_assert(scale<int>(mag_ratio<1, 3>, 9) == 3);
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// identity
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static_assert(scale<int>(mag<1>, 42) == 42);
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// floating-point path
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static_assert(scale<double>(mag_ratio<1, 2>, 1.0) == 0.5);
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static_assert(scale<float>(mag<3>, 1.0f) == 3.0f);
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// MagnitudeScalable concept
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static_assert(detail::MagnitudeScalable<int>);
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static_assert(detail::MagnitudeScalable<long>);
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static_assert(detail::MagnitudeScalable<double>);
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static_assert(detail::MagnitudeScalable<float>);
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// Irrational magnitude conversions with integer representation require explicit value_cast.
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// deg = (π/180) rad — the conversion factor is irrational, so every integer result is approximate.
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//
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// Positive: value_cast compiles and produces the expected truncated integer result.
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static_assert(value_cast<angular::degree>(1 * angular::radian).numerical_value_in(angular::degree) == 57);
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static_assert(value_cast<angular::radian>(180 * angular::degree).numerical_value_in(angular::radian) == 3);
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// Negative: implicit conversion is blocked at compile time to prevent accidental precision loss.
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static_assert(!std::is_convertible_v<quantity<angular::radian, int>, quantity<angular::degree, int>>);
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static_assert(!std::is_convertible_v<quantity<angular::degree, int>, quantity<angular::radian, int>>);
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// Large-value safety: deg -> grad uses factor 10/9. Being a pure rational, the
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// computation uses exact 128-bit integer arithmetic — correct on all platforms,
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// including ARM / Apple Silicon where long double == double (64-bit mantissa).
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static_assert(value_cast<angular::gradian>(std::int64_t{1'000'000'000'000'000'000} * angular::degree)
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.numerical_value_in(angular::gradian) == std::int64_t{1'111'111'111'111'111'111});
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} // namespace
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