From 1a4671024df651f79c745f38ecaaf45b677d460c Mon Sep 17 00:00:00 2001
From: Matt Borland <matt@mattborland.com>
Date: Thu, 6 Jul 2023 15:07:45 +0200
Subject: [PATCH] Improve rounding to 1 ULP

---
 include/boost/charconv/detail/bit_layouts.hpp    | 15 ---------------
 .../boost/charconv/detail/compute_float80.hpp    | 16 ++++------------
 2 files changed, 4 insertions(+), 27 deletions(-)

diff --git a/include/boost/charconv/detail/bit_layouts.hpp b/include/boost/charconv/detail/bit_layouts.hpp
index f4013aa..ae60363 100644
--- a/include/boost/charconv/detail/bit_layouts.hpp
+++ b/include/boost/charconv/detail/bit_layouts.hpp
@@ -87,21 +87,6 @@ struct IEEEl2bits
 #endif
 };
 
-struct IEEEl2bits_oneman
-{
-#if BOOST_CHARCONV_ENDIAN_LITTLE_BYTE
-    std::uint64_t mantissa : 64;
-    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::uint64_t mantissa : 64
-#endif
-};
-
 struct ieee754_binary80
 {
     static constexpr int significand_bits = 63;
diff --git a/include/boost/charconv/detail/compute_float80.hpp b/include/boost/charconv/detail/compute_float80.hpp
index 6fc736c..2000582 100644
--- a/include/boost/charconv/detail/compute_float80.hpp
+++ b/include/boost/charconv/detail/compute_float80.hpp
@@ -347,19 +347,11 @@ inline ResultType compute_float80(std::int64_t q, Unsigned_Integer w, bool negat
     return_val = negative ? -return_val : return_val;
 
     // Do we need to round?
-    IEEEl2bits_oneman bits;
-    std::memcpy(&bits, &return_val, sizeof(return_val));
-    if ((man & 1) != (bits.mantissa & 1))
+    if (!(man & 1))
     {
-        // Yes we should round
-        if (bits.mantissa & 1)
-        {
-            ++bits.mantissa;
-        }
-        else
-        {
-            --bits.mantissa;
-        }
+        IEEEl2bits bits;
+        std::memcpy(&bits, &return_val, sizeof(return_val));
+        ++bits.mantissa_l;
         std::memcpy(&return_val, &bits, sizeof(return_val));
     }
     success = std::errc();