Merge pull request #901 from cppalliance/900

Fix comparisons to zero

Author: mborland

include/boost/decimal/detail/comparison.hpp

@@ -101,6 +101,12 @@ BOOST_DECIMAL_FORCE_INLINE constexpr auto equality_impl(DecimalType lhs, Decimal
 template <BOOST_DECIMAL_FAST_DECIMAL_FLOATING_TYPE DecimalType>
 BOOST_DECIMAL_FORCE_INLINE constexpr auto fast_equality_impl(const DecimalType& lhs, const DecimalType& rhs) noexcept -> bool
 {
+    if (lhs.significand_ == 0U && rhs.significand_ == 0U)
+    {
+        // -0 == +0
+        return true;
+    }
+
     if (lhs.exponent_ != rhs.exponent_)
     {
         return false;
@@ -117,11 +123,6 @@ BOOST_DECIMAL_FORCE_INLINE constexpr auto fast_equality_impl(const DecimalType&
     }
     #endif
 
-    if (lhs.significand_ == 0U)
-    {
-        return true; // -0 == +0
-    }
-
     return lhs.sign_ == rhs.sign_;
 }
 

include/boost/decimal/detail/power_tables.hpp

@@ -208,17 +208,17 @@ static_assert(sizeof(emulated_256_pow10) == sizeof(boost::decimal::detail::uint2
 
 } // namespace impl
 
+#if defined(__GNUC__) && __GNUC__ >= 7
+#  pragma GCC diagnostic push
+#  pragma GCC diagnostic ignored "-Warray-bounds"
+#endif
+
 template <typename T>
 constexpr auto pow10(T n) noexcept -> T
 {
     return static_cast<T>(impl::powers_of_10[static_cast<std::size_t>(n)]);
 }
 
-#if defined(__GNUC__) && __GNUC__ >= 7
-#  pragma GCC diagnostic push
-#  pragma GCC diagnostic ignored "-Warray-bounds"
-#endif
-
 template <>
 constexpr auto pow10(const boost::int128::uint128_t n) noexcept -> boost::int128::uint128_t
 {

test/Jamfile

@@ -54,6 +54,7 @@ run github_issue_799.cpp ;
 run github_issue_802.cpp ;
 run github_issue_805.cpp ;
 run github_issue_808.cpp ;
+run github_issue_900.cpp ;
 run link_1.cpp link_2.cpp link_3.cpp ;
 run quick.cpp ;
 run random_decimal32_comp.cpp ;

test/github_issue_900.cpp

@@ -0,0 +1,36 @@
+// Copyright 2025 Matt Borland
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/decimal.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::decimal;
+
+template <typename Dec>
+void to_chars_helper()
+{
+    const Dec default_value;
+    char buffer[64];
+
+    const auto r = to_chars(buffer, buffer + sizeof(buffer), default_value);
+
+    if (BOOST_TEST(r))
+    {
+        *r.ptr = '\0';
+        BOOST_TEST_CSTR_EQ(buffer, "0.0e+00");
+    }
+}
+
+int main()
+{
+    to_chars_helper<decimal32>();
+    to_chars_helper<decimal64>();
+    to_chars_helper<decimal128>();
+
+    to_chars_helper<decimal32_fast>();
+    to_chars_helper<decimal64_fast>();
+    to_chars_helper<decimal128_fast>();
+
+    return boost::report_errors();
+}