Merge pull request #1159 from cppalliance/refactor_quantum

mborland · web-flow · commit c24dd80aabaa · 2025-10-22T18:20:08.000+02:00
diff --git a/include/boost/decimal/charconv.hpp b/include/boost/decimal/charconv.hpp
@@ -26,7 +26,6 @@
 #include <boost/decimal/detail/countl.hpp>
 #include <boost/decimal/detail/remove_trailing_zeros.hpp>
 #include <boost/decimal/detail/promotion.hpp>
-#include <boost/decimal/detail/quantum_preservation_format.hpp>
 
 #ifndef BOOST_DECIMAL_BUILD_MODULE
 #include <cstdint>
@@ -1110,9 +1109,19 @@ constexpr auto to_chars_hex_impl(char* first, char* last, const TargetDecimalTyp
     return to_chars_integer_impl<std::uint32_t>(first, last, static_cast<std::uint32_t>(abs_exp));
 }
 
+#ifdef _MSC_VER
+# pragma warning(push)
+# pragma warning(disable: 4702) // Unreachable code
+#endif
+
 template <BOOST_DECIMAL_DECIMAL_FLOATING_TYPE TargetDecimalType>
 constexpr auto to_chars_cohort_preserving_scientific(char* first, char* last, const TargetDecimalType& value) noexcept -> to_chars_result
 {
+    BOOST_DECIMAL_IF_CONSTEXPR (detail::is_fast_type_v<TargetDecimalType>)
+    {
+        return {last, std::errc::invalid_argument};
+    }
+
     using unsigned_integer = typename TargetDecimalType::significand_type;
 
     const auto fp = fpclassify(value);
@@ -1171,11 +1180,6 @@ constexpr auto to_chars_cohort_preserving_scientific(char* first, char* last, co
     return to_chars_integer_impl<std::uint32_t>(first, last, abs_exp);
 }
 
-#ifdef _MSC_VER
-# pragma warning(push)
-# pragma warning(disable: 4702) // Unreachable code
-#endif
-
 template <BOOST_DECIMAL_DECIMAL_FLOATING_TYPE TargetDecimalType>
 constexpr auto to_chars_impl(char* first, char* last, const TargetDecimalType& value, const chars_format fmt = chars_format::general, const int local_precision = -1) noexcept -> to_chars_result
 {
@@ -1212,6 +1216,20 @@ constexpr auto to_chars_impl(char* first, char* last, const TargetDecimalType& v
                 return to_chars_scientific_impl(first, last, value, fmt);
             case chars_format::hex:
                 return to_chars_hex_impl(first, last, value);
+            case chars_format::cohort_preserving_scientific:
+                BOOST_DECIMAL_IF_CONSTEXPR (detail::is_fast_type_v<TargetDecimalType>)
+                {
+                    // Fast types have no concept of cohorts
+                    return {last, std::errc::invalid_argument};
+                }
+
+                if (local_precision != -1)
+                {
+                    // Precision and cohort preservation are mutually exclusive options
+                    return {last, std::errc::invalid_argument};
+                }
+
+                return to_chars_cohort_preserving_scientific(first, last, value);
             // LCOV_EXCL_START
             default:
                 BOOST_DECIMAL_UNREACHABLE;
@@ -1243,34 +1261,6 @@ constexpr auto to_chars_impl(char* first, char* last, const TargetDecimalType& v
     return to_chars_scientific_impl(first, last, value, fmt, local_precision); // LCOV_EXCL_LINE
 }
 
-// TODO(mborland): Remove once other modes are inplace
-#ifdef _MSC_VER
-#  pragma warning(push)
-#  pragma warning(disable: 4065)
-#endif
-
-template <BOOST_DECIMAL_DECIMAL_FLOATING_TYPE TargetDecimalType>
-constexpr auto to_chars_impl(char* first, char* last, const TargetDecimalType& value, const chars_format fmt, const quantum_preservation method) noexcept -> to_chars_result
-{
-    // No quantum preservation is the same thing as regular to_chars
-    if (method == quantum_preservation::off)
-    {
-        return to_chars_impl(first, last, value, fmt);
-    }
-
-    // Sanity check our bounds
-    if (BOOST_DECIMAL_UNLIKELY(first >= last))
-    {
-        return {last, std::errc::invalid_argument};
-    }
-
-    switch (fmt)
-    {
-        default:
-            return to_chars_cohort_preserving_scientific(first, last, value);
-    }
-}
-
 #ifdef _MSC_VER
 # pragma warning(pop)
 #endif
@@ -1300,13 +1290,6 @@ constexpr auto to_chars(char* first, char* last, const TargetDecimalType& value,
     return detail::to_chars_impl(first, last, value, fmt, precision);
 }
 
-BOOST_DECIMAL_EXPORT template <BOOST_DECIMAL_DECIMAL_FLOATING_TYPE TargetDecimalType>
-constexpr auto to_chars(char* first, char* last, const TargetDecimalType& value, const chars_format fmt, const quantum_preservation method) noexcept -> to_chars_result
-{
-    static_assert(detail::is_ieee_type_v<TargetDecimalType>, "Fast types are automatically normalized, so they have no concept of quantum preservation");
-    return detail::to_chars_impl(first, last, value, fmt, method);
-}
-
 #ifdef BOOST_DECIMAL_HAS_STD_CHARCONV
 
 BOOST_DECIMAL_EXPORT template <typename DecimalType>
diff --git a/include/boost/decimal/decimal128_t.hpp b/include/boost/decimal/decimal128_t.hpp
@@ -207,7 +207,7 @@ BOOST_DECIMAL_EXPORT class decimal128_t final
 
     template <BOOST_DECIMAL_DECIMAL_FLOATING_TYPE TargetDecimalType>
     friend constexpr auto detail::to_chars_hex_impl(char* first, char* last, const TargetDecimalType& value) noexcept -> to_chars_result;
-
+    
     template <BOOST_DECIMAL_DECIMAL_FLOATING_TYPE TargetDecimalType>
     friend constexpr auto detail::to_chars_cohort_preserving_scientific(char* first, char* last, const TargetDecimalType& value) noexcept -> to_chars_result;
 
diff --git a/include/boost/decimal/decimal_fast128_t.hpp b/include/boost/decimal/decimal_fast128_t.hpp
@@ -70,6 +70,9 @@ constexpr auto to_chars_fixed_impl(char* first, char* last, const TargetDecimalT
 template <BOOST_DECIMAL_DECIMAL_FLOATING_TYPE TargetDecimalType>
 constexpr auto to_chars_hex_impl(char* first, char* last, const TargetDecimalType& value) noexcept -> to_chars_result;
 
+template <BOOST_DECIMAL_DECIMAL_FLOATING_TYPE TargetDecimalType>
+constexpr auto to_chars_cohort_preserving_scientific(char* first, char* last, const TargetDecimalType& value) noexcept -> to_chars_result;
+
 } // namespace detail
 
 #ifdef _MSC_VER
@@ -185,6 +188,9 @@ BOOST_DECIMAL_EXPORT class decimal_fast128_t final
     template <BOOST_DECIMAL_DECIMAL_FLOATING_TYPE TargetDecimalType>
     friend constexpr auto detail::to_chars_hex_impl(char* first, char* last, const TargetDecimalType& value) noexcept -> to_chars_result;
 
+    template <BOOST_DECIMAL_DECIMAL_FLOATING_TYPE TargetDecimalType>
+    friend constexpr auto detail::to_chars_cohort_preserving_scientific(char* first, char* last, const TargetDecimalType& value) noexcept -> to_chars_result;
+
     #if !defined(BOOST_DECIMAL_DISABLE_CLIB)
     constexpr decimal_fast128_t(const char* str, std::size_t len);
     #endif
diff --git a/include/boost/decimal/decimal_fast32_t.hpp b/include/boost/decimal/decimal_fast32_t.hpp
@@ -65,6 +65,9 @@ constexpr auto to_chars_fixed_impl(char* first, char* last, const TargetDecimalT
 template <BOOST_DECIMAL_DECIMAL_FLOATING_TYPE TargetDecimalType>
 constexpr auto to_chars_hex_impl(char* first, char* last, const TargetDecimalType& value) noexcept -> to_chars_result;
 
+template <BOOST_DECIMAL_DECIMAL_FLOATING_TYPE TargetDecimalType>
+constexpr auto to_chars_cohort_preserving_scientific(char* first, char* last, const TargetDecimalType& value) noexcept -> to_chars_result;
+
 template <bool checked, BOOST_DECIMAL_DECIMAL_FLOATING_TYPE T>
 constexpr auto d32_fma_impl(T x, T y, T z) noexcept -> T;
 
@@ -182,6 +185,9 @@ BOOST_DECIMAL_EXPORT class decimal_fast32_t final
     template <BOOST_DECIMAL_DECIMAL_FLOATING_TYPE TargetDecimalType>
     friend constexpr auto detail::to_chars_hex_impl(char* first, char* last, const TargetDecimalType& value) noexcept -> to_chars_result;
 
+    template <BOOST_DECIMAL_DECIMAL_FLOATING_TYPE TargetDecimalType>
+    friend constexpr auto detail::to_chars_cohort_preserving_scientific(char* first, char* last, const TargetDecimalType& value) noexcept -> to_chars_result;
+
     template <typename DecimalType, typename T>
     friend constexpr auto detail::generic_div_impl(const T& lhs, const T& rhs) noexcept -> DecimalType;
 
diff --git a/include/boost/decimal/decimal_fast64_t.hpp b/include/boost/decimal/decimal_fast64_t.hpp
@@ -67,6 +67,9 @@ constexpr auto to_chars_fixed_impl(char* first, char* last, const TargetDecimalT
 template <BOOST_DECIMAL_DECIMAL_FLOATING_TYPE TargetDecimalType>
 constexpr auto to_chars_hex_impl(char* first, char* last, const TargetDecimalType& value) noexcept -> to_chars_result;
 
+template <BOOST_DECIMAL_DECIMAL_FLOATING_TYPE TargetDecimalType>
+constexpr auto to_chars_cohort_preserving_scientific(char* first, char* last, const TargetDecimalType& value) noexcept -> to_chars_result;
+
 template <bool checked, BOOST_DECIMAL_DECIMAL_FLOATING_TYPE T>
 constexpr auto d64_fma_impl(T x, T y, T z) noexcept -> T;
 
@@ -189,6 +192,9 @@ BOOST_DECIMAL_EXPORT class decimal_fast64_t final
     template <BOOST_DECIMAL_DECIMAL_FLOATING_TYPE TargetDecimalType>
     friend constexpr auto detail::to_chars_hex_impl(char* first, char* last, const TargetDecimalType& value) noexcept -> to_chars_result;
 
+    template <BOOST_DECIMAL_DECIMAL_FLOATING_TYPE TargetDecimalType>
+    friend constexpr auto detail::to_chars_cohort_preserving_scientific(char* first, char* last, const TargetDecimalType& value) noexcept -> to_chars_result;
+
     template <bool checked, BOOST_DECIMAL_DECIMAL_FLOATING_TYPE T>
     friend constexpr auto detail::d64_fma_impl(T x, T y, T z) noexcept -> T;
 
diff --git a/include/boost/decimal/detail/chars_format.hpp b/include/boost/decimal/detail/chars_format.hpp
@@ -17,6 +17,7 @@ BOOST_DECIMAL_EXPORT enum class chars_format : unsigned
     scientific = 1 << 0,
     fixed = 1 << 1,
     hex = 1 << 2,
+    cohort_preserving_scientific = 1 << 3,
     general = fixed | scientific
 };
 
diff --git a/include/boost/decimal/detail/concepts.hpp b/include/boost/decimal/detail/concepts.hpp
@@ -267,11 +267,11 @@ concept fast_decimal_floating_point_type = boost::decimal::detail::is_fast_type_
 #define BOOST_DECIMAL_OUTPUT_ITER(I, T) boost::decimal::detail::concepts::output_iterator<I, T>
 #define BOOST_DECIMAL_REQUIRES_ITER(X) requires X
 
-#define BOOST_DECIMAL_REQUIRES(X, T) -> T requires X<T>
-#define BOOST_DECIMAL_REQUIRES_TWO(X1, T1, X2, T2) -> detail::promote_args_t<T1, T2> requires X1<T1> && X2<T2>
-#define BOOST_DECIMAL_REQUIRES_TWO_RETURN(X1, T1, X2, T2, ReturnType) -> ReturnType requires X1<T1> && X2<T2>
-#define BOOST_DECIMAL_REQUIRES_THREE(X1, T1, X2, T2, X3, T3) -> detail::promote_args_t<T1, T2, T3> requires X1<T1> && X2<T2> && X3<T3>
-#define BOOST_DECIMAL_REQUIRES_RETURN(X, T, ReturnType) -> ReturnType requires X<T>
+#define BOOST_DECIMAL_REQUIRES(X, T) -> T requires (X<T>)
+#define BOOST_DECIMAL_REQUIRES_TWO(X1, T1, X2, T2) -> detail::promote_args_t<T1, T2> requires (X1<T1> && X2<T2>)
+#define BOOST_DECIMAL_REQUIRES_TWO_RETURN(X1, T1, X2, T2, ReturnType) -> ReturnType requires (X1<T1> && X2<T2>)
+#define BOOST_DECIMAL_REQUIRES_THREE(X1, T1, X2, T2, X3, T3) -> detail::promote_args_t<T1, T2, T3> requires (X1<T1> && X2<T2> && X3<T3>)
+#define BOOST_DECIMAL_REQUIRES_RETURN(X, T, ReturnType) -> ReturnType requires (X<T>)
 
 #ifdef BOOST_DECIMAL_EXEC_COMPATIBLE
 #include <execution>
diff --git a/include/boost/decimal/detail/quantum_preservation_format.hpp b/include/boost/decimal/detail/quantum_preservation_format.hpp
diff --git a/test/test_to_chars_quantum.cpp b/test/test_to_chars_quantum.cpp
@@ -22,28 +22,12 @@ void test_to_chars_scientific(const ResultsType& decimals, const StringsType& st
     for (std::size_t i {}; i < decimals.size(); ++i)
     {
         char buffer[64] {};
-        const auto r {to_chars(buffer, buffer + sizeof(buffer), decimals[i], chars_format::scientific, quantum_preservation::on)};
+        const auto r {to_chars(buffer, buffer + sizeof(buffer), decimals[i], chars_format::cohort_preserving_scientific)};
         BOOST_TEST(r);
         *r.ptr = '\0';
 
         BOOST_TEST_CSTR_EQ(buffer, strings[i]);
     }
-
-    for (std::size_t i {}; i < decimals.size(); ++i)
-    {
-        char quantum_buffer[64] {};
-        const auto r_quantum {to_chars(quantum_buffer, quantum_buffer + sizeof(quantum_buffer), decimals[i], chars_format::scientific, quantum_preservation::off)};
-        BOOST_TEST(r_quantum);
-        *r_quantum.ptr = '\0';
-
-        char buffer[64] {};
-        const auto r {to_chars(buffer, buffer + sizeof(buffer), decimals[i], chars_format::scientific)};
-        BOOST_TEST(r);
-        *r.ptr = '\0';
-
-        BOOST_TEST_CSTR_EQ(quantum_buffer, buffer);
-        BOOST_TEST_CSTR_EQ(quantum_buffer, strings[0]);
-    }
 }
 
 template <typename T>
