Floating-point negative zero doesn't match positive zero in the index
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Key: CORE-3547
URL: http://tracker.firebirdsql.org/browse/CORE-3547
Project: Firebird Core
Issue Type: Bug
Components: Engine
Affects Versions: 2.1.4, 2.5.0, 2.0.6, 3.0 Initial, 1.5.6, 2.1.3, 2.1.2,
2.0.5, 2.1.1, 2.0.4, 2.1.0
Reporter: Dmitry Yemanov
The IEEE representation of single- and double-precision floating point values
distinguish between positive and negative zeros. When they're compared
naturally (using compiler generated code), everything is okay. But if they're
stored in the index, they get compared byte-wise. As a result, searching for
the negative zero cannot find the positive zero, and vice versa.
Test case:
select count(*) from rdb$relations where rdb$relation_id = 0
-- result = 1
select count(*) from rdb$relations where rdb$relation_id = 0e0
-- result = 1
select count(*) from rdb$relations where rdb$relation_id = (1e0 - 1e0)
-- result = 1
select count(*) from rdb$relations where rdb$relation_id = -0e0
-- result = 0
select count(*) from rdb$relations where rdb$relation_id = -(1e0 - 1e0)
-- result = 0
In dialect 1 it could be reproduced without explicit floating point values:
select count(*) from rdb$relations where rdb$relation_id = (1 - 1)
-- result = 1
select count(*) from rdb$relations where rdb$relation_id = -(1 - 1)
-- result = 0
At the same time:
select count(*) from rdb$database where 0e0 = -0e0
-- result = 1, as no index is involved
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