Add in the initial support for DPD conversions

doc/decimal/conversions.adoc

@@ -5,11 +5,12 @@ https://www.boost.org/LICENSE_1_0.txt
 ////
 
 [#conversions]
-= Fast Type Conversions
+= Bit Conversions
 :idprefix: conversions_
 
-Since we have non-IEEE 754 compliant types we offer a set of functions that allow their conversion to and from the IEEE 754 compliant BID layout.
-These functions allow lossless conversion with more compact storage.
+IEEE 754 specifies two different encodings for decimal floating point types: Binary Integer Significand Field (BID), and Densely Packed Decimal Significand Field (DPD).
+Internally this library is implemented in the BID format for the IEEE-754 compliant types.
+Should the user want to capture the bit format in BID or convert to DPD we offer a family of conversion functions: `to_bid`, `from_bid`, `to_dpd`, and `from_dpd` that allow conversion to or from the bit strings regardless of encoding.
 
 [source, c++]
 ----
@@ -26,6 +27,8 @@ struct uint128
 
 } // namespace detail
 
+// ----- BID Conversions -----
+
 BOOST_DECIMAL_CXX20_CONSTEXPR std::uint32_t to_bid_d32(decimal32 val) noexcept;
 
 BOOST_DECIMAL_CXX20_CONSTEXPR std::uint32_t to_bid_d32f(decimal32_fast val) noexcept;
@@ -48,6 +51,18 @@ BOOST_DECIMAL_CXX20_CONSTEXPR T from_bid(std::uint64_t bits) noexcept;
 template <typename T = decimal128>
 BOOST_DECIMAL_CXX20_CONSTEXPR T from_bid(detail::uint128 bits) noexcept;
 
+// ----- DPD Conversions -----
+
+constexpr std::uint32_t to_dpd_d32(decimal32 val) noexcept;
+
+constexpr std::uint32_t to_dpd_d32f(decimal32_fast val) noexcept;
+
+template <typename T>
+constexpr auto to_dpd(T val) noexcept;
+
+template <typename T = decimal32_fast>
+constexpr T from_dpd(std::uint32_t bits) noexcept;
+
 } // namespace decimal
 } // namespace boost
 ----

include/boost/decimal.hpp

@@ -40,6 +40,7 @@
 #include <boost/decimal/detail/io.hpp>
 #include <boost/decimal/cstdio.hpp>
 #include <boost/decimal/bid_conversion.hpp>
+#include <boost/decimal/dpd_conversion.hpp>
 
 #if defined(__clang__) && !defined(__GNUC__)
 #  pragma clang diagnostic pop

include/boost/decimal/decimal32.hpp

@@ -218,6 +218,10 @@ BOOST_DECIMAL_EXPORT class decimal32 final // NOLINT(cppcoreguidelines-special-m
     template <BOOST_DECIMAL_DECIMAL_FLOATING_TYPE DecimalType>
     friend constexpr auto sequential_less_impl(DecimalType lhs, DecimalType rhs) noexcept -> bool;
 
+    template <typename DecimalType>
+    friend constexpr auto to_dpd_d32(DecimalType val) noexcept
+    BOOST_DECIMAL_REQUIRES_RETURN(detail::is_decimal_floating_point_v, DecimalType, std::uint32_t);
+
 public:
     // 3.2.2.1 construct/copy/destroy:
     constexpr decimal32() noexcept = default;

include/boost/decimal/decimal32_fast.hpp

@@ -114,6 +114,10 @@ class decimal32_fast final
         -> std::enable_if_t<(detail::is_decimal_floating_point_v<Decimal1> &&
                              detail::is_decimal_floating_point_v<Decimal2>), bool>;
 
+    template <typename DecimalType>
+    friend constexpr auto to_dpd_d32(DecimalType val) noexcept
+    BOOST_DECIMAL_REQUIRES_RETURN(detail::is_decimal_floating_point_v, DecimalType, std::uint32_t);
+
 public:
     constexpr decimal32_fast() noexcept {}