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fix: order -NaN below +NaN in Literal comparison #861

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fix: order -NaN below +NaN in Literal comparison #861

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95350e9
fix: order -NaN below +NaN in Literal comparison (#860)
LuciferYang Jul 29, 2026
76e7fd1
test: construct signed NaNs with std::copysign
LuciferYang Jul 29, 2026
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4 changes: 3 additions & 1 deletion src/iceberg/expression/literal.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -444,7 +444,9 @@ std::strong_ordering CompareFloat(T lhs, T rhs) {
// and -NAN < NAN.
bool lhs_is_negative = std::signbit(lhs);
bool rhs_is_negative = std::signbit(rhs);
return lhs_is_negative <=> rhs_is_negative;
// A negative sign bit sorts below a positive one (-NaN < +NaN), so a
// negative operand must compare as less.
return rhs_is_negative <=> lhs_is_negative;
Comment on lines +447 to +449

@LuciferYang LuciferYang Jul 30, 2026

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Keeping rhs <=> lhs: it's the idiom for reversing the order relation, and the comment above states the intent. The SignedNaNComparison tests pin the direction either way.

}

namespace {
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25 changes: 25 additions & 0 deletions src/iceberg/test/literal_test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@

#include "iceberg/expression/literal.h"

#include <cmath>
#include <limits>
#include <numbers>
#include <unordered_set>
Expand Down Expand Up @@ -216,6 +217,18 @@ TEST(LiteralTest, FloatNaNComparison) {
EXPECT_EQ(nan1 <=> signaling_nan, std::partial_ordering::equivalent);
}

TEST(LiteralTest, FloatSignedNaNComparison) {
auto neg_nan =
Literal::Float(std::copysign(std::numeric_limits<float>::quiet_NaN(), -1.0f));
auto pos_nan =
Literal::Float(std::copysign(std::numeric_limits<float>::quiet_NaN(), +1.0f));

// Per the total ordering -NaN < ... < +NaN, a negative NaN sorts below a
// positive NaN.
EXPECT_EQ(neg_nan <=> pos_nan, std::partial_ordering::less);
EXPECT_EQ(pos_nan <=> neg_nan, std::partial_ordering::greater);
}

TEST(LiteralTest, FloatInfinityComparison) {
auto neg_inf = Literal::Float(-std::numeric_limits<float>::infinity());
auto pos_inf = Literal::Float(std::numeric_limits<float>::infinity());
Expand Down Expand Up @@ -267,6 +280,18 @@ TEST(LiteralTest, DoubleNaNComparison) {
EXPECT_EQ(nan1 <=> signaling_nan, std::partial_ordering::equivalent);
}

TEST(LiteralTest, DoubleSignedNaNComparison) {
auto neg_nan =
Literal::Double(std::copysign(std::numeric_limits<double>::quiet_NaN(), -1.0));
auto pos_nan =
Literal::Double(std::copysign(std::numeric_limits<double>::quiet_NaN(), +1.0));

// Per the total ordering -NaN < ... < +NaN, a negative NaN sorts below a
// positive NaN.
EXPECT_EQ(neg_nan <=> pos_nan, std::partial_ordering::less);
EXPECT_EQ(pos_nan <=> neg_nan, std::partial_ordering::greater);
}

TEST(LiteralTest, DoubleInfinityComparison) {
auto neg_inf = Literal::Double(-std::numeric_limits<double>::infinity());
auto pos_inf = Literal::Double(std::numeric_limits<double>::infinity());
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