Charconv is used to serialize doubles

include/boost/json/detail/impl/format.ipp

@@ -12,8 +12,9 @@
 #define BOOST_JSON_DETAIL_IMPL_FORMAT_IPP
 
 #include <boost/charconv/to_chars.hpp>
-#include <boost/json/detail/ryu/detail/common.hpp>
+#include <cmath>
 #include <cstring>
+#include <limits>
 
 namespace boost {
 namespace json {
@@ -115,35 +116,59 @@ unsigned
 format_double(
     char* dest, double d, bool allow_infinity_and_nan) noexcept
 {
-    namespace ryud = ryu::detail;
-    // Copyright 2018 Ulf Adams
-    //
-    // Decode bits into sign, mantissa, and exponent.
-    std::uint64_t const bits = ryud::double_to_bits(d);
-    const bool ieeeSign = ((bits >> (ryud::DOUBLE_MANTISSA_BITS + ryud::DOUBLE_EXPONENT_BITS)) & 1) != 0;
-    const std::uint64_t ieeeMantissa = bits & ((1ull << ryud::DOUBLE_MANTISSA_BITS) - 1);
-    const std::uint32_t ieeeExponent = (std::uint32_t)((bits >> ryud::DOUBLE_MANTISSA_BITS) & ((1u << ryud::DOUBLE_EXPONENT_BITS) - 1));
-    // Case distinction; exit early for the easy cases.
-    if(BOOST_JSON_UNLIKELY(
-        ieeeExponent == ((1u << ryud::DOUBLE_EXPONENT_BITS) - 1u) ||
-        (ieeeExponent == 0
-          && ieeeMantissa == 0) ))
+    charconv::to_chars_result result;
+
+    using Limits = std::numeric_limits<double>;
+
+    if(BOOST_JSON_UNLIKELY( std::isnan(d) ))
     {
-        // We changed how special numbers are output by default
-        if (allow_infinity_and_nan)
-            return ryud::copy_special_str(
-                dest, ieeeSign, ieeeExponent != 0, ieeeMantissa != 0);
+        if( allow_infinity_and_nan )
+        {
+            std::memcpy(dest, "NaN", 3);
+            result.ptr = dest + 3;
+        }
         else
-            return ryud::copy_special_str_conforming(
-                dest, ieeeSign, ieeeExponent != 0, ieeeMantissa != 0);
-
+        {
+            std::memcpy(dest, "null", 4);
+            result.ptr = dest + 4;
+        }
+    }
+    else if(BOOST_JSON_UNLIKELY( d == Limits::infinity() ))
+    {
+        if( allow_infinity_and_nan )
+        {
+            std::memcpy(dest, "Infinity", 8);
+            result.ptr = dest + 8;
+        }
+        else
+        {
+            std::memcpy(dest, "1e99999", 7);
+            result.ptr = dest + 7;
+        }
+    }
+    else if(BOOST_JSON_UNLIKELY( d == -Limits::infinity() ))
+    {
+        if( allow_infinity_and_nan )
+        {
+            std::memcpy(dest, "-Infinity", 9);
+            result.ptr = dest + 9;
+        }
+        else
+        {
+            std::memcpy(dest, "-1e99999", 8);
+            result.ptr = dest + 8;
+        }
+    }
+    else
+    {
+        result = charconv::to_chars(
+            dest,
+            dest + detail::max_number_chars,
+            d,
+            charconv::chars_format::scientific);
+        BOOST_ASSERT( result.ec == std::errc() );
     }
 
-    auto const result = charconv::to_chars(
-        dest,
-        dest + detail::max_number_chars,
-        d,
-        charconv::chars_format::scientific);
     return result.ptr - dest;
 }