Merge pull request #815 from cppalliance/811

Make -0 = +0
cppalliance · Jan 21, 2025 · b4f8cad · b4f8cad
2 parents 6aa62b9 + f25014b
commit b4f8cad
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Showing 11 changed files with 99 additions and 36 deletions.
diff --git a/include/boost/decimal/decimal128.hpp b/include/boost/decimal/decimal128.hpp
@@ -194,6 +194,9 @@ BOOST_DECIMAL_EXPORT class decimal128 final
     template <BOOST_DECIMAL_DECIMAL_FLOATING_TYPE TargetType, BOOST_DECIMAL_DECIMAL_FLOATING_TYPE Decimal>
     friend constexpr auto to_decimal(Decimal val) noexcept -> TargetType;
 
+    template <BOOST_DECIMAL_DECIMAL_FLOATING_TYPE DecimalType>
+    friend BOOST_DECIMAL_FORCE_INLINE constexpr auto equality_impl(DecimalType lhs, DecimalType rhs) noexcept -> bool;
+
     // Equality template between any integer type and decimal128
     template <BOOST_DECIMAL_DECIMAL_FLOATING_TYPE Decimal, BOOST_DECIMAL_INTEGRAL Integer>
     friend constexpr auto mixed_equality_impl(Decimal lhs, Integer rhs) noexcept
@@ -1202,16 +1205,7 @@ constexpr auto operator-(decimal128 rhs) noexcept-> decimal128
 
 constexpr auto operator==(decimal128 lhs, decimal128 rhs) noexcept -> bool
 {
-    #ifndef BOOST_DECIMAL_FAST_MATH
-    // Check for IEEE requirement that nan != nan
-    if (isnan(lhs) || isnan(rhs))
-    {
-        return false;
-    }
-    #endif
-
-    return equal_parts_impl<decimal128>(lhs.full_significand(), lhs.biased_exponent(), lhs.isneg(),
-                                        rhs.full_significand(), rhs.biased_exponent(), rhs.isneg());
+    return equality_impl(lhs, rhs);
 }
 
 template <typename Integer>

diff --git a/include/boost/decimal/decimal128_fast.hpp b/include/boost/decimal/decimal128_fast.hpp
@@ -537,16 +537,28 @@ constexpr auto not_finite(const decimal128_fast& val) noexcept -> bool
 
 constexpr auto operator==(const decimal128_fast& lhs, const decimal128_fast& rhs) noexcept -> bool
 {
+    if (lhs.exponent_ != rhs.exponent_)
+    {
+        return false;
+    }
+    if (lhs.significand_ != rhs.significand_)
+    {
+        return false;
+    }
+
     #ifndef BOOST_DECIMAL_FAST_MATH
-    if (isnan(lhs) || isnan(rhs))
+    if (isnan(lhs))
     {
         return false;
     }
     #endif
 
-    return lhs.sign_ == rhs.sign_ &&
-           lhs.exponent_ == rhs.exponent_ &&
-           lhs.significand_ == rhs.significand_;
+    if (lhs.significand_ == 0)
+    {
+        return true; // -0 == +0
+    }
+
+    return lhs.sign_ == rhs.sign_;
 }
 
 template <typename Integer>

diff --git a/include/boost/decimal/decimal32_fast.hpp b/include/boost/decimal/decimal32_fast.hpp
@@ -490,13 +490,28 @@ constexpr auto isfinite(decimal32_fast val) noexcept -> bool
 
 constexpr auto operator==(decimal32_fast lhs, decimal32_fast rhs) noexcept -> bool
 {
-    return
-           #ifndef BOOST_DECIMAL_FAST_MATH
-           !isnan(lhs) && !isnan(rhs) &&
-           #endif
-           (lhs.sign_ == rhs.sign_) &&
-           (lhs.exponent_ == rhs.exponent_) &&
-           (lhs.significand_ == rhs.significand_);
+    if (lhs.exponent_ != rhs.exponent_)
+    {
+        return false;
+    }
+    if (lhs.significand_ != rhs.significand_)
+    {
+        return false;
+    }
+
+    #ifndef BOOST_DECIMAL_FAST_MATH
+    if (isnan(lhs))
+    {
+        return false;
+    }
+    #endif
+
+    if (lhs.significand_ == 0)
+    {
+        return true; // -0 == +0
+    }
+
+    return lhs.sign_ == rhs.sign_;
 }
 
 constexpr auto operator!=(decimal32_fast lhs, decimal32_fast rhs) noexcept -> bool

diff --git a/include/boost/decimal/decimal64_fast.hpp b/include/boost/decimal/decimal64_fast.hpp
@@ -518,16 +518,28 @@ constexpr auto not_finite(decimal64_fast val) noexcept -> bool
 
 constexpr auto operator==(decimal64_fast lhs, decimal64_fast rhs) noexcept -> bool
 {
+    if (lhs.exponent_ != rhs.exponent_)
+    {
+        return false;
+    }
+    if (lhs.significand_ != rhs.significand_)
+    {
+        return false;
+    }
+
     #ifndef BOOST_DECIMAL_FAST_MATH
-    if (isnan(lhs) || isnan(rhs))
+    if (isnan(lhs))
     {
         return false;
     }
     #endif
 
-    return lhs.sign_ == rhs.sign_ &&
-           lhs.exponent_ == rhs.exponent_ &&
-           lhs.significand_ == rhs.significand_;
+    if (lhs.significand_ == 0)
+    {
+        return true; // -0 == +0
+    }
+
+    return lhs.sign_ == rhs.sign_;
 }
 
 template <typename Integer>

diff --git a/include/boost/decimal/detail/comparison.hpp b/include/boost/decimal/detail/comparison.hpp
@@ -38,7 +38,21 @@ BOOST_DECIMAL_FORCE_INLINE constexpr auto equality_impl(DecimalType lhs, Decimal
     }
     #endif
 
-    // Step 3: Check signs
+    // Step 2: Fast path
+    if (lhs.bits_ == rhs.bits_)
+    {
+        return true;
+    }
+
+    // Step 3: Check -0 == +0
+    auto lhs_sig {lhs.full_significand()};
+    auto rhs_sig {rhs.full_significand()};
+    if (lhs_sig == 0 && rhs_sig == 0)
+    {
+        return true;
+    }
+
+    // Step 4: Check signs
     const auto lhs_neg {lhs.isneg()};
     const auto rhs_neg {rhs.isneg()};
 
@@ -47,27 +61,19 @@ BOOST_DECIMAL_FORCE_INLINE constexpr auto equality_impl(DecimalType lhs, Decimal
         return false;
     }
 
-    // Step 4: Check the exponents
+    // Step 5: Check the exponents
     // If the difference is greater than we can represent in the significand than we can assume they are different
     const auto lhs_exp {lhs.biased_exponent()};
     const auto rhs_exp {rhs.biased_exponent()};
 
-    auto lhs_sig {lhs.full_significand()};
-    auto rhs_sig {rhs.full_significand()};
-
     const auto delta_exp {lhs_exp - rhs_exp};
 
-    if (lhs_sig == 0 && rhs_sig == 0)
-    {
-        // The difference in exponent is irrelevant here
-        return true;
-    }
     if (delta_exp > detail::precision_v<DecimalType> || delta_exp < -detail::precision_v<DecimalType>)
     {
         return false;
     }
 
-    // Step 5: Normalize the significand and compare
+    // Step 6: Normalize the significand and compare
     // Instead of multiplying the larger number, divide the smaller one
     if (delta_exp >= 0)
     {

diff --git a/test/random_decimal128_comp.cpp b/test/random_decimal128_comp.cpp
@@ -574,5 +574,9 @@ int main()
     random_mixed_SPACESHIP(std::numeric_limits<unsigned long long>::min(), std::numeric_limits<unsigned long long>::max());
     #endif
 
+    constexpr auto pos_zero = boost::decimal::decimal128{0, 0, false};
+    constexpr auto neg_zero = boost::decimal::decimal128{0, 0, true};
+    BOOST_TEST(pos_zero == neg_zero);
+
     return boost::report_errors();
 }
diff --git a/test/random_decimal128_fast_comp.cpp b/test/random_decimal128_fast_comp.cpp
@@ -593,5 +593,9 @@ int main()
     random_mixed_SPACESHIP(std::numeric_limits<unsigned long long>::min(), std::numeric_limits<unsigned long long>::max());
     #endif
 
+    constexpr auto pos_zero = boost::decimal::decimal128_fast{0, 0, false};
+    constexpr auto neg_zero = boost::decimal::decimal128_fast{0, 0, true};
+    BOOST_TEST_EQ(pos_zero, neg_zero);
+
     return boost::report_errors();
 }
diff --git a/test/random_decimal32_comp.cpp b/test/random_decimal32_comp.cpp
@@ -606,5 +606,9 @@ int main()
     random_mixed_SPACESHIP(std::numeric_limits<unsigned long long>::min(), std::numeric_limits<unsigned long long>::max());
     #endif
 
+    constexpr auto pos_zero = boost::decimal::decimal32{0, 0, false};
+    constexpr auto neg_zero = boost::decimal::decimal32{0, 0, true};
+    BOOST_TEST_EQ(pos_zero, neg_zero);
+
     return boost::report_errors();
 }
diff --git a/test/random_decimal32_fast_comp.cpp b/test/random_decimal32_fast_comp.cpp
@@ -593,5 +593,9 @@ int main()
     random_mixed_SPACESHIP(std::numeric_limits<unsigned long long>::min(), std::numeric_limits<unsigned long long>::max());
     #endif
 
+    constexpr auto pos_zero = boost::decimal::decimal32_fast{0, 0, false};
+    constexpr auto neg_zero = boost::decimal::decimal32_fast{0, 0, true};
+    BOOST_TEST_EQ(pos_zero, neg_zero);
+
     return boost::report_errors();
 }
diff --git a/test/random_decimal64_comp.cpp b/test/random_decimal64_comp.cpp
@@ -571,5 +571,9 @@ int main()
     random_mixed_SPACESHIP(std::numeric_limits<unsigned long long>::min(), std::numeric_limits<unsigned long long>::max());
     #endif
 
+    constexpr auto pos_zero = boost::decimal::decimal64{0, 0, false};
+    constexpr auto neg_zero = boost::decimal::decimal64{0, 0, true};
+    BOOST_TEST_EQ(pos_zero, neg_zero);
+
     return boost::report_errors();
 }
diff --git a/test/random_decimal64_fast_comp.cpp b/test/random_decimal64_fast_comp.cpp
@@ -593,5 +593,9 @@ int main()
     random_mixed_SPACESHIP(std::numeric_limits<unsigned long long>::min(), std::numeric_limits<unsigned long long>::max());
     #endif
 
+    constexpr auto pos_zero = boost::decimal::decimal64_fast{0, 0, false};
+    constexpr auto neg_zero = boost::decimal::decimal64_fast{0, 0, true};
+    BOOST_TEST_EQ(pos_zero, neg_zero);
+
     return boost::report_errors();
 }