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trunc(x) on a column turns -0.0 into 0.0

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#25,702 1 comment 0 reactions 1 assignee View on GitHub

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@1fanwang is already working on this.

Since Sep 25, 2026.

Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
75/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
rust, sql
Domain
databases

Research direction

Look for the trunc function implementation in the DataFusion codebase, likely in a file like expr/scalar.rs or expr/builtin.rs. The bug is in the columnar path where x == 0_f64 is used. Replace that condition with a check that preserves the sign, perhaps using x.trunc() directly. Write a test in the corresponding test module to verify trunc(-0.0) returns -0.0 for a column. Run the existing SQL function tests to ensure no regressions.

Written by the indexing model from the issue text.

Description

trunc(x) drops the sign of -0.0, but only when it runs on a column. On a scalar, and for trunc(x, 0), the sign is kept.

SELECT trunc(column1), trunc(column1, 0) FROM (VALUES (CAST(-0.0 AS DOUBLE)));
-- got:      0.0, -0.0
-- expected: -0.0, -0.0

The column code path returns 0.0 for either zero:

if x == 0_f64 { 0_f64 } else { x.trunc() }

-0.0 == 0.0 is true, so -0.0 becomes 0.0. f64::trunc already keeps the sign, so plain x.trunc() would be enough.

Seen through Lance (pylance 12.0.0): trunc(x, 0) on a -0.0 column returns -0.0. This line is the same on main and in 55.1.0. I found no existing issue or PR for it.

Dominant language
Rust
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Forks
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Avg merge
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Merged PRs (30d)
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