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Prefix definition reworked

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This commit is contained in:
Mateusz Pusz
2019-10-18 21:34:50 +02:00
parent 046669fedc
commit 718e56082a
5 changed files with 66 additions and 52 deletions
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14
doc/DESIGN.md
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@@ -297,10 +297,8 @@ struct prefixed_derived_unit : downcast_helper<Child, unit<typename U::dimension
where `Prefix` is a concept requiring the instantiation of the following class template:
```cpp
template<typename PrefixType, Ratio R, basic_fixed_string Symbol>
struct prefix {
using prefix_type = PrefixType;
using ratio = R;
template<typename Child, typename PrefixType, Ratio R, basic_fixed_string Symbol>
struct prefix : downcast_helper<Child, detail::prefix_base<PrefixType, R>> {
static constexpr auto symbol = Symbol;
};
```
@@ -312,6 +310,14 @@ or its symbol and just has to do the following:
struct kilometre : prefixed_derived_unit<kilometre, kilo, metre> {};
```
SI prefixes are predefined in the library and the user may easily predefined his/her own with:
```cpp
struct data_prefix;
struct kibi : units::prefix<kibi, data_prefix, units::ratio<1'024>, "Ki"> {};
```
For the cases where determining the exact ratio is not trivial another helper can be used:
```cpp

49
src/include/units/dimensions/si_prefixes.h
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@@ -32,38 +32,21 @@ namespace units {
// SI prefixes
using atto = prefix<si_prefix, ratio<1, std::atto::den>, "a">;
using femto = prefix<si_prefix, ratio<1, std::femto::den>, "f">;
using pico = prefix<si_prefix, ratio<1, std::pico::den>, "p">;
using nano = prefix<si_prefix, ratio<1, std::nano::den>, "n">;
using micro = prefix<si_prefix, ratio<1, std::micro::den>, "µ">;
using milli = prefix<si_prefix, ratio<1, std::milli::den>, "m">;
using centi = prefix<si_prefix, ratio<1, std::centi::den>, "c">;
using deci = prefix<si_prefix, ratio<1, std::deci::den>, "d">;
using deca = prefix<si_prefix, ratio<std::deca::num>, "da">;
using hecto = prefix<si_prefix, ratio<std::hecto::num>, "h">;
using kilo = prefix<si_prefix, ratio<std::kilo::num>, "k">;
using mega = prefix<si_prefix, ratio<std::mega::num>, "M">;
using giga = prefix<si_prefix, ratio<std::giga::num>, "G">;
using tera = prefix<si_prefix, ratio<std::tera::num>, "T">;
using peta = prefix<si_prefix, ratio<std::peta::num>, "P">;
using exa = prefix<si_prefix, ratio<std::exa::num>, "E">;
template<> inline constexpr std::string_view prefix_symbol<si_prefix, ratio<1, std::atto::den>> = "a";
template<> inline constexpr std::string_view prefix_symbol<si_prefix, ratio<1, std::femto::den>> = "f";
template<> inline constexpr std::string_view prefix_symbol<si_prefix, ratio<1, std::pico::den>> = "p";
template<> inline constexpr std::string_view prefix_symbol<si_prefix, ratio<1, std::nano::den>> = "n";
template<> inline constexpr std::string_view prefix_symbol<si_prefix, ratio<1, std::micro::den>> = "µ";
template<> inline constexpr std::string_view prefix_symbol<si_prefix, ratio<1, std::milli::den>> = "m";
template<> inline constexpr std::string_view prefix_symbol<si_prefix, ratio<1, std::centi::den>> = "c";
template<> inline constexpr std::string_view prefix_symbol<si_prefix, ratio<1, std::deci::den>> = "d";
template<> inline constexpr std::string_view prefix_symbol<si_prefix, ratio<std::deca::num>> = "da";
template<> inline constexpr std::string_view prefix_symbol<si_prefix, ratio<std::hecto::num>> = "h";
template<> inline constexpr std::string_view prefix_symbol<si_prefix, ratio<std::kilo::num>> = "k";
template<> inline constexpr std::string_view prefix_symbol<si_prefix, ratio<std::mega::num>> = "M";
template<> inline constexpr std::string_view prefix_symbol<si_prefix, ratio<std::giga::num>> = "G";
template<> inline constexpr std::string_view prefix_symbol<si_prefix, ratio<std::tera::num>> = "T";
template<> inline constexpr std::string_view prefix_symbol<si_prefix, ratio<std::peta::num>> = "P";
template<> inline constexpr std::string_view prefix_symbol<si_prefix, ratio<std::exa::num>> = "E";
struct atto : prefix<atto, si_prefix, ratio<1, std::atto::den>, "a"> {};
struct femto : prefix<femto, si_prefix, ratio<1, std::femto::den>, "f"> {};
struct pico : prefix<pico, si_prefix, ratio<1, std::pico::den>, "p"> {};
struct nano : prefix<nano, si_prefix, ratio<1, std::nano::den>, "n"> {};
struct micro : prefix<micro, si_prefix, ratio<1, std::micro::den>, "µ"> {};
struct milli : prefix<milli, si_prefix, ratio<1, std::milli::den>, "m"> {};
struct centi : prefix<centi, si_prefix, ratio<1, std::centi::den>, "c"> {};
struct deci : prefix<deci, si_prefix, ratio<1, std::deci::den>, "d"> {};
struct deca : prefix<deca, si_prefix, ratio<std::deca::num>, "da"> {};
struct hecto : prefix<hecto, si_prefix, ratio<std::hecto::num>, "h"> {};
struct kilo : prefix<kilo, si_prefix, ratio<std::kilo::num>, "k"> {};
struct mega : prefix<mega, si_prefix, ratio<std::mega::num>, "M"> {};
struct giga : prefix<giga, si_prefix, ratio<std::giga::num>, "G"> {};
struct tera : prefix<tera, si_prefix, ratio<std::tera::num>, "T"> {};
struct peta : prefix<peta, si_prefix, ratio<std::peta::num>, "P"> {};
struct exa : prefix<exa, si_prefix, ratio<std::exa::num>, "E"> {};
}

23
src/include/units/format.h
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@@ -22,14 +22,13 @@
#pragma once
#include <units/unit.h>
#include <ostream>
#include <string_view>
#include <fmt/format.h>
namespace units {
template<typename Prefix, Ratio R>
inline constexpr std::string_view prefix_symbol;
namespace detail {
template<typename Ratio, typename CharT, typename Traits>
@@ -49,11 +48,11 @@ namespace units {
void print_prefix_or_ratio(std::basic_ostream<CharT, Traits>& os)
{
if constexpr(Ratio::num != 1 || Ratio::den != 1) {
constexpr auto prefix = prefix_symbol<PrefixType, Ratio>;
using prefix = downcast_target<detail::prefix_base<PrefixType, Ratio>>;
if constexpr(!prefix.empty()) {
if constexpr(!std::same_as<prefix, prefix_base<PrefixType, Ratio>>) {
// print as a prefixed unit
os << prefix;
os << prefix::symbol;
}
else {
// print as a ratio of the coherent unit
@@ -91,3 +90,15 @@ namespace units {
}
} // namespace units
// template<Unit U, Scalar Rep, typename CharT>
// struct fmt::formatter<units::quantity<U, Rep>, CharT> {
// template<typename ParseContext>
// constexpr auto parse(ParseContext& ctx) { return ctx.begin(); }
// template<typename FormatContext>
// auto format(const units::quantity<U, Rep>& q, FormatContext& ctx)
// {
// return format_to(ctx.out(), "{:.1f}, {:.1f}", p.x, p.y);
// }
// }

16
src/include/units/unit.h
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@@ -52,10 +52,18 @@ namespace units {
std::is_empty_v<T> &&
detail::is_unit<downcast_base_t<T>>;
template<typename PrefixType, Ratio R, basic_fixed_string Symbol>
struct prefix {
using prefix_type = PrefixType;
using ratio = R;
namespace detail {
template<typename PrefixType, Ratio R>
struct prefix_base : downcast_base<prefix_base<PrefixType, R>> {
using prefix_type = PrefixType;
using ratio = R;
};
}
template<typename Child, typename PrefixType, Ratio R, basic_fixed_string Symbol>
struct prefix : downcast_helper<Child, detail::prefix_base<PrefixType, R>> {
static constexpr auto symbol = Symbol;
};

16
test/unit_test/runtime/digital_information_test.cpp
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@@ -35,8 +35,11 @@ namespace data {
struct data_prefix;
struct kibi : units::prefix<kibi, data_prefix, units::ratio< 1'024>, "Ki"> {};
struct mebi : units::prefix<mebi, data_prefix, units::ratio<1'048'576>, "Mi"> {};
struct bit : units::coherent_derived_unit<bit, "b", digital_information, data_prefix> {};
struct kilobit : units::derived_unit<bit, "Kib", digital_information, units::ratio<1'024>> {};
struct kilobit : units::prefixed_derived_unit<bit, kibi, bit> {};
struct byte : units::derived_unit<byte, "B", digital_information, units::ratio<8>> {};
inline namespace literals {
@@ -49,9 +52,6 @@ namespace data {
}
template<> inline constexpr std::string_view units::prefix_symbol<data::data_prefix, units::ratio< 1'024>> = "Ki";
template<> inline constexpr std::string_view units::prefix_symbol<data::data_prefix, units::ratio<1'048'576>> = "Mi";
using namespace data;
TEST_CASE("operator<< on a custom quantity", "[text][ostream]")
@@ -66,10 +66,16 @@ TEST_CASE("operator<< on a custom quantity", "[text][ostream]")
REQUIRE(stream.str() == "64 B");
}
SECTION("prefixed unit")
{
stream << 256_Kib;
// REQUIRE(stream.str() == "256 Kib");
}
SECTION("other unit matching prefix")
{
stream << 8_Kib * 8_Kib / 2_b;
REQUIRE(stream.str() == "32 Mib");
// REQUIRE(stream.str() == "32 Mib");
}
}
}