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Fix integer comparison bug #5211

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Merged
nlohmann merged 8 commits into from
Aug 12, 2026
Merged

Fix integer comparison bug #5211

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d7206e4
Fix integer comparison bug
ljcjclljc Jun 17, 2026
5d3e37c
commit
ljcjclljc Jun 17, 2026
52ba8cb
Remove generated CI artifacts and update amalgamation
ljcjclljc Jun 18, 2026
6ac2269
Silence cpplint braces warning in comparison macro
ljcjclljc Jun 18, 2026
f1d1d67
Update amalgamation after cpplint fix
ljcjclljc Jun 18, 2026
8b37696
Add mixed signed and unsigned comparison regression test
ljcjclljc Jul 4, 2026
33cd77b
Clarify mixed signed and unsigned comparison handling
ljcjclljc Jul 4, 2026
8ca9f00
Expand mixed signed and unsigned comparison tests
ljcjclljc Jul 5, 2026
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16 changes: 13 additions & 3 deletions include/nlohmann/json.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3652,6 +3652,12 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec

// note parentheses around operands are necessary; see
// https://github.com/nlohmann/json/issues/1530
// Mixed signed/unsigned integer comparisons check whether the signed value
// is negative before casting. If it is, the comparison is performed with
// the fixed values -1 and 1, which preserves the ordering relationship
// because any negative signed value is smaller than any unsigned value.
// Otherwise, the non-negative signed value is cast to unsigned before the
// comparison to avoid wraparound.
#define JSON_IMPLEMENT_OPERATOR(op, null_result, unordered_result, default_result) \
const auto lhs_type = lhs.type(); \
const auto rhs_type = rhs.type(); \
Expand Down Expand Up @@ -3710,12 +3716,16 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
} \
else if (lhs_type == value_t::number_unsigned && rhs_type == value_t::number_integer) \
{ \
return static_cast<number_integer_t>(lhs.m_data.m_value.number_unsigned) op rhs.m_data.m_value.number_integer; \
return (rhs.m_data.m_value.number_integer < 0) \
? (number_integer_t(1) op number_integer_t(-1)) \
: (lhs.m_data.m_value.number_unsigned op static_cast<number_unsigned_t>(rhs.m_data.m_value.number_integer)); \
} \
else if (lhs_type == value_t::number_integer && rhs_type == value_t::number_unsigned) \
{ \
return lhs.m_data.m_value.number_integer op static_cast<number_integer_t>(rhs.m_data.m_value.number_unsigned); \
} \
return (lhs.m_data.m_value.number_integer < 0) \
? (number_integer_t(-1) op number_integer_t(1)) \
: (static_cast<number_unsigned_t>(lhs.m_data.m_value.number_integer) op rhs.m_data.m_value.number_unsigned); \
} \
else if(compares_unordered(lhs, rhs))\
{\
return (unordered_result);\
Expand Down
16 changes: 13 additions & 3 deletions single_include/nlohmann/json.hpp
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Expand Up @@ -24388,6 +24388,12 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec

// note parentheses around operands are necessary; see
// https://github.com/nlohmann/json/issues/1530
// Mixed signed/unsigned integer comparisons check whether the signed value
// is negative before casting. If it is, the comparison is performed with
// the fixed values -1 and 1, which preserves the ordering relationship
// because any negative signed value is smaller than any unsigned value.
// Otherwise, the non-negative signed value is cast to unsigned before the
// comparison to avoid wraparound.
#define JSON_IMPLEMENT_OPERATOR(op, null_result, unordered_result, default_result) \
const auto lhs_type = lhs.type(); \
const auto rhs_type = rhs.type(); \
Expand Down Expand Up @@ -24446,12 +24452,16 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
} \
else if (lhs_type == value_t::number_unsigned && rhs_type == value_t::number_integer) \
{ \
return static_cast<number_integer_t>(lhs.m_data.m_value.number_unsigned) op rhs.m_data.m_value.number_integer; \
return (rhs.m_data.m_value.number_integer < 0) \
? (number_integer_t(1) op number_integer_t(-1)) \
: (lhs.m_data.m_value.number_unsigned op static_cast<number_unsigned_t>(rhs.m_data.m_value.number_integer)); \
} \
else if (lhs_type == value_t::number_integer && rhs_type == value_t::number_unsigned) \
{ \
return lhs.m_data.m_value.number_integer op static_cast<number_integer_t>(rhs.m_data.m_value.number_unsigned); \
} \
return (lhs.m_data.m_value.number_integer < 0) \
? (number_integer_t(-1) op number_integer_t(1)) \
: (static_cast<number_unsigned_t>(lhs.m_data.m_value.number_integer) op rhs.m_data.m_value.number_unsigned); \
} \
else if(compares_unordered(lhs, rhs))\
{\
return (unordered_result);\
Expand Down
71 changes: 71 additions & 0 deletions tests/src/unit-comparison.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,8 @@

#include "doctest_compatibility.h"

#include <cstdint>

#define JSON_TESTS_PRIVATE
#include <nlohmann/json.hpp>
using nlohmann::json;
Expand Down Expand Up @@ -255,6 +257,75 @@ TEST_CASE("lexicographical comparison operators")
{f_, f_, f_, f_, f_, f_, f_, f_, f_, f_, f_, f_, f_, f_, f_, f_, f_, f_, f_, f_, f_, f_}, // 21
};

SECTION("signed/unsigned mixed comparison above INT64_MAX")
{
const json above_int64_max = static_cast<std::uint64_t>((std::numeric_limits<std::int64_t>::max)()) + 1ULL;
const json max_uint64 = (std::numeric_limits<std::uint64_t>::max)();
const json negative_one = -1;
const json one = 1;
const json max_int64 = (std::numeric_limits<std::int64_t>::max)();

CHECK_FALSE(above_int64_max == negative_one);
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CHECK(above_int64_max != negative_one);
CHECK(negative_one < above_int64_max);
CHECK(negative_one <= above_int64_max);
CHECK_FALSE(negative_one > above_int64_max);
CHECK_FALSE(negative_one >= above_int64_max);
CHECK_FALSE(above_int64_max < negative_one);
CHECK_FALSE(above_int64_max <= negative_one);
CHECK(above_int64_max > negative_one);
CHECK(above_int64_max >= negative_one);
CHECK(negative_one != above_int64_max);
CHECK_FALSE(negative_one == above_int64_max);

CHECK_FALSE(max_uint64 == negative_one);
CHECK(max_uint64 != negative_one);
CHECK(negative_one < max_uint64);
CHECK(negative_one <= max_uint64);
CHECK_FALSE(negative_one > max_uint64);
CHECK_FALSE(negative_one >= max_uint64);
CHECK_FALSE(max_uint64 < negative_one);
CHECK_FALSE(max_uint64 <= negative_one);
CHECK(max_uint64 > negative_one);
CHECK(max_uint64 >= negative_one);
CHECK(negative_one != max_uint64);
CHECK_FALSE(negative_one == max_uint64);

CHECK_FALSE(one == above_int64_max);
CHECK(one != above_int64_max);
CHECK(one < above_int64_max);
CHECK(one <= above_int64_max);
CHECK_FALSE(one > above_int64_max);
CHECK_FALSE(one >= above_int64_max);
CHECK_FALSE(above_int64_max < one);
CHECK_FALSE(above_int64_max <= one);
CHECK(above_int64_max > one);
CHECK(above_int64_max >= one);

CHECK_FALSE(max_int64 == above_int64_max);
CHECK(max_int64 != above_int64_max);
CHECK(max_int64 < above_int64_max);
CHECK(max_int64 <= above_int64_max);
CHECK_FALSE(max_int64 > above_int64_max);
CHECK_FALSE(max_int64 >= above_int64_max);
CHECK_FALSE(above_int64_max < max_int64);
CHECK_FALSE(above_int64_max <= max_int64);
CHECK(above_int64_max > max_int64);
CHECK(above_int64_max >= max_int64);

#if JSON_HAS_THREE_WAY_COMPARISON
// JSON_HAS_CPP_20 (do not remove; see note at top of file)
CHECK((negative_one <=> above_int64_max) == std::partial_ordering::less); // *NOPAD*
CHECK((above_int64_max <=> negative_one) == std::partial_ordering::greater); // *NOPAD*
CHECK((negative_one <=> max_uint64) == std::partial_ordering::less); // *NOPAD*
CHECK((max_uint64 <=> negative_one) == std::partial_ordering::greater); // *NOPAD*
CHECK((one <=> above_int64_max) == std::partial_ordering::less); // *NOPAD*
CHECK((above_int64_max <=> one) == std::partial_ordering::greater); // *NOPAD*
CHECK((max_int64 <=> above_int64_max) == std::partial_ordering::less); // *NOPAD*
CHECK((above_int64_max <=> max_int64) == std::partial_ordering::greater); // *NOPAD*
#endif
}

SECTION("compares unordered")
{
std::vector<std::vector<bool>> expected =
Expand Down
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