mirror of
https://github.com/nlohmann/json.git
synced 2026-09-06 02:18:14 +00:00
137a40b9aa
The mixed number arms of JSON_IMPLEMENT_OPERATOR cast the integer to number_float_t before comparing. Past the float's mantissa that cast is lossy: 2^63-2 and 2^63-1 both round to 2^63, so each compares equal to that float while differing from each other. Equality is therefore intransitive and the ordering is not a strict weak ordering, which makes std::sort over such values, or using them as keys in std::set or std::map, undefined behavior. Compare the two exactly instead. The integer's range is a power of two the float represents exactly, so a float outside it is ordered by magnitude alone; inside it, truncating the float is exact, and the integer parts and then any fractional part decide. The helper hands back a pair whose comparison with the original operator reproduces that ordering, which keeps every operator's return type as it was, including partial_ordering for the spaceship. A NaN operand is returned in both members, so NaN stays false for the relational operators and unordered for <=>. Values a float represents exactly still compare equal, so json(1) == json(1.0) is unchanged. Signed-off-by: qatcod <79017227+qatcod@users.noreply.github.com>