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Fix handling of inf times negative values #1303

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4f41cb0
Make reproducer test set
mborland Jan 16, 2026
b0a255d
Fix decimal32 logic
mborland Jan 16, 2026
ae75755
Port logic to other types
mborland Jan 16, 2026
958ff9a
Fix test logic
mborland Jan 16, 2026
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25 changes: 25 additions & 0 deletions include/boost/decimal/decimal128_t.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1771,6 +1771,22 @@ constexpr auto operator*(const decimal128_t& lhs, const decimal128_t& rhs) noexc
{
return from_bits(detail::d128_nan_mask);
}
else if (isinf(lhs) && !isnan(rhs) && (signbit(lhs) != signbit(rhs)))
{
return signbit(lhs) ? lhs : -lhs;
}
else if (isinf(lhs) && !isnan(rhs) && (signbit(lhs) == signbit(rhs)))
{
return signbit(lhs) ? -lhs : lhs;
}
else if (isinf(rhs) && !isnan(lhs) && (signbit(rhs) != signbit(lhs)))
{
return signbit(rhs) ? rhs : -rhs;
}
else if (isinf(rhs) && !isnan(lhs) && (signbit(rhs) == signbit(lhs)))
{
return signbit(rhs) ? -rhs : rhs;
}

return detail::check_non_finite(lhs, rhs);
}
Expand All @@ -1793,6 +1809,15 @@ constexpr auto operator*(const decimal128_t lhs, const Integer rhs) noexcept
#ifndef BOOST_DECIMAL_FAST_MATH
if (not_finite(lhs))
{
if (isinf(lhs) && (signbit(lhs) != (rhs < 0)))
{
return signbit(lhs) ? lhs : -lhs;
}
else if (isinf(lhs) && (signbit(lhs) == (rhs < 0)))
{
return signbit(lhs) ? -lhs : lhs;
}

return detail::check_non_finite(lhs);
}
#endif
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25 changes: 25 additions & 0 deletions include/boost/decimal/decimal32_t.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1772,6 +1772,22 @@ constexpr auto operator*(const decimal32_t lhs, const decimal32_t rhs) noexcept
{
return from_bits(detail::d32_nan_mask);
}
else if (isinf(lhs) && !isnan(rhs) && (signbit(lhs) != signbit(rhs)))
{
return signbit(lhs) ? lhs : -lhs;
}
else if (isinf(lhs) && !isnan(rhs) && (signbit(lhs) == signbit(rhs)))
{
return signbit(lhs) ? -lhs : lhs;
}
else if (isinf(rhs) && !isnan(lhs) && (signbit(rhs) != signbit(lhs)))
{
return signbit(rhs) ? rhs : -rhs;
}
else if (isinf(rhs) && !isnan(lhs) && (signbit(rhs) == signbit(lhs)))
{
return signbit(rhs) ? -rhs : rhs;
}

return detail::check_non_finite(lhs, rhs);
}
Expand All @@ -1793,6 +1809,15 @@ constexpr auto operator*(const decimal32_t lhs, const Integer rhs) noexcept
#ifndef BOOST_DECIMAL_FAST_MATH
if (!isfinite(lhs))
{
if (isinf(lhs) && (signbit(lhs) != (rhs < 0)))
{
return signbit(lhs) ? lhs : -lhs;
}
else if (isinf(lhs) && (signbit(lhs) == (rhs < 0)))
{
return signbit(lhs) ? -lhs : lhs;
}

return detail::check_non_finite(lhs);
}
#endif
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25 changes: 25 additions & 0 deletions include/boost/decimal/decimal64_t.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1774,6 +1774,22 @@ constexpr auto operator*(const decimal64_t lhs, const decimal64_t rhs) noexcept
{
return from_bits(detail::d64_nan_mask);
}
else if (isinf(lhs) && !isnan(rhs) && (signbit(lhs) != signbit(rhs)))
{
return signbit(lhs) ? lhs : -lhs;
}
else if (isinf(lhs) && !isnan(rhs) && (signbit(lhs) == signbit(rhs)))
{
return signbit(lhs) ? -lhs : lhs;
}
else if (isinf(rhs) && !isnan(lhs) && (signbit(rhs) != signbit(lhs)))
{
return signbit(rhs) ? rhs : -rhs;
}
else if (isinf(rhs) && !isnan(lhs) && (signbit(rhs) == signbit(lhs)))
{
return signbit(rhs) ? -rhs : rhs;
}

return detail::check_non_finite(lhs, rhs);
}
Expand All @@ -1795,6 +1811,15 @@ constexpr auto operator*(const decimal64_t lhs, const Integer rhs) noexcept
#ifndef BOOST_DECIMAL_FAST_MATH
if (not_finite(lhs))
{
if (isinf(lhs) && (signbit(lhs) != (rhs < 0)))
{
return signbit(lhs) ? lhs : -lhs;
}
else if (isinf(lhs) && (signbit(lhs) == (rhs < 0)))
{
return signbit(lhs) ? -lhs : lhs;
}

return detail::check_non_finite(lhs);
}
#endif
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25 changes: 25 additions & 0 deletions include/boost/decimal/decimal_fast128_t.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1129,6 +1129,22 @@ constexpr auto operator*(const decimal_fast128_t& lhs, const decimal_fast128_t&
{
return direct_init_d128(detail::d128_fast_qnan, 0, false);
}
else if (isinf(lhs) && !isnan(rhs) && (signbit(lhs) != signbit(rhs)))
{
return signbit(lhs) ? lhs : -lhs;
}
else if (isinf(lhs) && !isnan(rhs) && (signbit(lhs) == signbit(rhs)))
{
return signbit(lhs) ? -lhs : lhs;
}
else if (isinf(rhs) && !isnan(lhs) && (signbit(rhs) != signbit(lhs)))
{
return signbit(rhs) ? rhs : -rhs;
}
else if (isinf(rhs) && !isnan(lhs) && (signbit(rhs) == signbit(lhs)))
{
return signbit(rhs) ? -rhs : rhs;
}

return detail::check_non_finite(lhs, rhs);
}
Expand All @@ -1147,6 +1163,15 @@ constexpr auto operator*(const decimal_fast128_t& lhs, const Integer rhs) noexce
#ifndef BOOST_DECIMAL_FAST_MATH
if (not_finite(lhs))
{
if (isinf(lhs) && (signbit(lhs) != (rhs < 0)))
{
return signbit(lhs) ? lhs : -lhs;
}
else if (isinf(lhs) && (signbit(lhs) == (rhs < 0)))
{
return signbit(lhs) ? -lhs : lhs;
}

return detail::check_non_finite(lhs);
}
#endif
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25 changes: 25 additions & 0 deletions include/boost/decimal/decimal_fast32_t.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1123,6 +1123,22 @@ constexpr auto operator*(const decimal_fast32_t lhs, const decimal_fast32_t rhs)
{
return direct_init(detail::d32_fast_qnan, UINT8_C(0));
}
else if (isinf(lhs) && !isnan(rhs) && (signbit(lhs) != signbit(rhs)))
{
return signbit(lhs) ? lhs : -lhs;
}
else if (isinf(lhs) && !isnan(rhs) && (signbit(lhs) == signbit(rhs)))
{
return signbit(lhs) ? -lhs : lhs;
}
else if (isinf(rhs) && !isnan(lhs) && (signbit(rhs) != signbit(lhs)))
{
return signbit(rhs) ? rhs : -rhs;
}
else if (isinf(rhs) && !isnan(lhs) && (signbit(rhs) == signbit(lhs)))
{
return signbit(rhs) ? -rhs : rhs;
}

return detail::check_non_finite(lhs, rhs);
}
Expand All @@ -1141,6 +1157,15 @@ constexpr auto operator*(const decimal_fast32_t lhs, const Integer rhs) noexcept
#ifndef BOOST_DECIMAL_FAST_MATH
if (!isfinite(lhs))
{
if (isinf(lhs) && (signbit(lhs) != (rhs < 0)))
{
return signbit(lhs) ? lhs : -lhs;
}
else if (isinf(lhs) && (signbit(lhs) == (rhs < 0)))
{
return signbit(lhs) ? -lhs : lhs;
}

return detail::check_non_finite(lhs);
}
#endif
Expand Down
25 changes: 25 additions & 0 deletions include/boost/decimal/decimal_fast64_t.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1248,6 +1248,22 @@ constexpr auto operator*(const decimal_fast64_t lhs, const decimal_fast64_t rhs)
{
return direct_init_d64(detail::d64_fast_qnan, 0, false);
}
else if (isinf(lhs) && !isnan(rhs) && (signbit(lhs) != signbit(rhs)))
{
return signbit(lhs) ? lhs : -lhs;
}
else if (isinf(lhs) && !isnan(rhs) && (signbit(lhs) == signbit(rhs)))
{
return signbit(lhs) ? -lhs : lhs;
}
else if (isinf(rhs) && !isnan(lhs) && (signbit(rhs) != signbit(lhs)))
{
return signbit(rhs) ? rhs : -rhs;
}
else if (isinf(rhs) && !isnan(lhs) && (signbit(rhs) == signbit(lhs)))
{
return signbit(rhs) ? -rhs : rhs;
}

return detail::check_non_finite(lhs, rhs);
}
Expand All @@ -1266,6 +1282,15 @@ constexpr auto operator*(const decimal_fast64_t lhs, const Integer rhs) noexcept
#ifndef BOOST_DECIMAL_FAST_MATH
if (not_finite(lhs))
{
if (isinf(lhs) && (signbit(lhs) != (rhs < 0)))
{
return signbit(lhs) ? lhs : -lhs;
}
else if (isinf(lhs) && (signbit(lhs) == (rhs < 0)))
{
return signbit(lhs) ? -lhs : lhs;
}

return detail::check_non_finite(lhs);
}
#endif
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1 change: 1 addition & 0 deletions test/Jamfile
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Original file line number Diff line number Diff line change
Expand Up @@ -84,6 +84,7 @@ run github_issue_1174.cpp ;
run github_issue_1260.cpp ;
run github_issue_1294.cpp ;
run github_issue_1299.cpp ;
run github_issue_1302.cpp ;

run link_1.cpp link_2.cpp link_3.cpp ;
run quick.cpp ;
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65 changes: 65 additions & 0 deletions test/github_issue_1302.cpp
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Original file line number Diff line number Diff line change
@@ -0,0 +1,65 @@
// Copyright 2026 Matt Borland
// Distributed under the Boost Software License, Version 1.0.
// https://www.boost.org/LICENSE_1_0.txt
//
// See: https://github.com/cppalliance/decimal/issues/1294

#include <boost/decimal.hpp>
#include <boost/core/lightweight_test.hpp>
#include <limits>

using namespace boost::decimal;

template <typename T>
void test()
{
// Positive LHS, Positive RHS
BOOST_TEST_EQ(std::numeric_limits<T>::infinity() * std::numeric_limits<T>::infinity(), std::numeric_limits<T>::infinity());
BOOST_TEST_EQ(std::numeric_limits<T>::infinity() * T{1000}, std::numeric_limits<T>::infinity());
BOOST_TEST_EQ(std::numeric_limits<T>::infinity() * 1000, std::numeric_limits<T>::infinity());
BOOST_TEST_EQ(T{1000} * std::numeric_limits<T>::infinity(), std::numeric_limits<T>::infinity());
BOOST_TEST_EQ(1000 * std::numeric_limits<T>::infinity(), std::numeric_limits<T>::infinity());
BOOST_TEST(isnan(std::numeric_limits<T>::infinity() * std::numeric_limits<T>::quiet_NaN()));
BOOST_TEST(isnan(std::numeric_limits<T>::quiet_NaN() * std::numeric_limits<T>::infinity()));

// Positive LHS, Negative RHS
BOOST_TEST_EQ(std::numeric_limits<T>::infinity() * -std::numeric_limits<T>::infinity(), -std::numeric_limits<T>::infinity());
BOOST_TEST_EQ(std::numeric_limits<T>::infinity() * -T{1000}, -std::numeric_limits<T>::infinity());
BOOST_TEST_EQ(std::numeric_limits<T>::infinity() * -1000, -std::numeric_limits<T>::infinity());
BOOST_TEST_EQ(T{1000} * -std::numeric_limits<T>::infinity(), -std::numeric_limits<T>::infinity());
BOOST_TEST_EQ(1000 * -std::numeric_limits<T>::infinity(), -std::numeric_limits<T>::infinity());
BOOST_TEST(isnan(std::numeric_limits<T>::infinity() * -std::numeric_limits<T>::quiet_NaN()));
BOOST_TEST(isnan(std::numeric_limits<T>::quiet_NaN() * -std::numeric_limits<T>::infinity()));

// Negative RHS, positive LHS
BOOST_TEST_EQ(-std::numeric_limits<T>::infinity() * std::numeric_limits<T>::infinity(), -std::numeric_limits<T>::infinity());
BOOST_TEST_EQ(-std::numeric_limits<T>::infinity() * T{1000}, -std::numeric_limits<T>::infinity());
BOOST_TEST_EQ(-std::numeric_limits<T>::infinity() * 1000, -std::numeric_limits<T>::infinity());
BOOST_TEST_EQ(-T{1000} * std::numeric_limits<T>::infinity(), -std::numeric_limits<T>::infinity());
BOOST_TEST_EQ(-1000 * std::numeric_limits<T>::infinity(), -std::numeric_limits<T>::infinity());
BOOST_TEST(isnan(-std::numeric_limits<T>::infinity() * std::numeric_limits<T>::quiet_NaN()));
BOOST_TEST(isnan(-std::numeric_limits<T>::quiet_NaN() * std::numeric_limits<T>::infinity()));

// Negative RHS, Negative RHS
BOOST_TEST_EQ(-std::numeric_limits<T>::infinity() * -std::numeric_limits<T>::infinity(), std::numeric_limits<T>::infinity());
BOOST_TEST_EQ(-std::numeric_limits<T>::infinity() * -T{1000}, std::numeric_limits<T>::infinity());
BOOST_TEST_EQ(-std::numeric_limits<T>::infinity() * -1000, std::numeric_limits<T>::infinity());
BOOST_TEST_EQ(-T{1000} * -std::numeric_limits<T>::infinity(), std::numeric_limits<T>::infinity());
BOOST_TEST_EQ(-1000 * -std::numeric_limits<T>::infinity(), std::numeric_limits<T>::infinity());
BOOST_TEST(isnan(-std::numeric_limits<T>::infinity() * -std::numeric_limits<T>::quiet_NaN()));
BOOST_TEST(isnan(-std::numeric_limits<T>::quiet_NaN() * -std::numeric_limits<T>::infinity()));

}

int main()
{
test<decimal32_t>();
test<decimal64_t>();
test<decimal128_t>();

test<decimal_fast32_t>();
test<decimal_fast64_t>();
test<decimal_fast128_t>();

return boost::report_errors();
}
2 changes: 1 addition & 1 deletion test/test_to_chars.cpp
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Expand Up @@ -80,7 +80,7 @@ void test_error_value(const char* input, chars_format format, int precision = -1
template <typename T>
void test_non_finite_values()
{
std::uniform_real_distribution<float> dist(-1.0, 1.0);
std::uniform_real_distribution<float> dist(0.0f, 1.0f);

const auto formats = {chars_format::fixed, chars_format::scientific, chars_format::general, chars_format::hex};

Expand Down