Add layouts for floating point types and LDBL size macros

include/boost/charconv/detail/bit_layouts.hpp

@@ -0,0 +1,112 @@
+// Copyright 2023 Matt Borland
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#ifndef BOOST_CHARCONV_DETAIL_BIT_LAYOUTS_HPP
+#define BOOST_CHARCONV_DETAIL_BIT_LAYOUTS_HPP
+
+#include <boost/charconv/detail/config.hpp>
+#include <cstdint>
+#include <cfloat>
+
+// Layouts of floating point types as specified by IEEE 754
+
+namespace boost { namespace charconv { namespace detail {
+
+struct IEEEf2bits
+{
+#if BOOST_CHARCONV_ENDIAN_LITTLE_BYTE
+    std::uint32_t mantissa : 23;
+    std::uint32_t exponent : 8;
+    std::uint32_t sign : 1;
+#else // Big endian
+    std::uint32_t sign : 1;
+    std::uint32_t exponent : 8;
+    std::uint32_t mantissa : 23;
+#endif 
+};
+
+struct IEEEd2bits
+{
+#if BOOST_CHARCONV_ENDIAN_LITTLE_BYTE
+    std::uint32_t mantissa_l : 32;
+    std::uint32_t mantissa_h : 20;
+    std::uint32_t exponent : 11;
+    std::uint32_t sign : 1;
+#else // Big endian
+    std::uint32_t sign : 1;
+    std::uint32_t exponent : 11;
+    std::uint32_t mantissa_h : 20;
+    std::uint32_t mantissa_l : 32;
+#endif
+};
+
+// 80 bit long double (e.g. x86-64)
+#if LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384
+
+struct IEEEl2bits
+{
+#if BOOST_CHARCONV_ENDIAN_LITTLE_BYTE
+    std::uint32_t mantissa_l : 32;
+    std::uint32_t mantissa_h : 32;
+    std::uint32_t exponent : 15;
+    std::uint32_t sign : 1;
+    std::uint32_t pad : 32;
+#else // Big endian
+    std::uint32_t pad : 32;
+    std::uint32_t sign : 1;
+    std::uint32_t exponent : 15;
+    std::uint32_t mantissa_h : 32;
+    std::uint32_t mantissa_l : 32;
+#endif
+};
+
+#define BOOST_CHARCONV_LDBL_BITS 80
+
+// 128 bit long double (e.g. s390x, ppcle64)
+#elif LDBL_MANT_DIG == 113 && LDBL_MAX_EXP == 16384
+
+struct IEEEl2bits
+{
+#if BOOST_CHARCONV_ENDIAN_LITTLE_BYTE
+    std::uint64_t mantissa_l : 64;
+    std::uint64_t mantissa_h : 48;
+    std::uint32_t exponent : 15;
+    std::uint32_t sign : 1;
+#else // Big endian
+    std::uint32_t sign : 1;
+    std::uint32_t exponent : 15;
+    std::uint64_t mantissa_h : 48;
+    std::uint64_t mantissa_l : 64;
+#endif
+};
+
+#define BOOST_CHARCONV_LDBL_BITS 128
+
+// 64 bit long double (double == long double on ARM)
+#elif LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
+
+struct IEEEl2bits
+{
+#if BOOST_CHARCONV_ENDIAN_LITTLE_BYTE
+    std::uint32_t mantissa_l : 32;
+    std::uint32_t mantissa_h : 20;
+    std::uint32_t exponent : 11;
+    std::uint32_t sign : 1;
+#else // Big endian
+    std::uint32_t sign : 1;
+    std::uint32_t exponent : 11;
+    std::uint32_t mantissa_h : 20;
+    std::uint32_t mantissa_l : 32;
+#endif
+};
+
+#define BOOST_CHARCONV_LDBL_BITS 64
+
+#else // Unsupported long double representation
+#  define BOOST_MATH_UNSUPPORTED_LONG_DOUBLE
+#endif
+
+}}} // Namespaces
+
+#endif // BOOST_CHARCONV_DETAIL_BIT_LAYOUTS_HPP