berkaysynnada commented on PR #16745:
URL: https://github.com/apache/datafusion/pull/16745#issuecomment-3065030622
Currently, when computing the next representable float from +0.0 or -0.0,
the behavior incorrectly skips directly to the smallest subnormal (±ε) instead
of transitioning between -0.0 and +0.0. For example, next_down(+0.0) returns
-ε, but we expect it to return -0.0. Similarly, next_up(-0.0) returns +ε, but
we expect it to return +0.0.
This causes intervals like [-0.0, -ε] instead of the expected [-0.0, -0.0].
In ScalarValue comparisons we already treat -0.0 and +0.0 as NOT equal, but the
rounding logic was skipping over them and jumping directly to subnormals.
To fix this, I locally updated next_up and next_down to handle ±0.0
explicitly. In next_up, if the input is -0.0, it now returns +0.0 instead of
+ε. In next_down, if the input is +0.0, it now returns -0.0 instead of -ε. All
other cases remain as they were. This keeps the fix localized to the specific
±0.0 boundary without unnecessarily affecting the general behavior of interval
arithmetic logic.
```rust
pub fn next_up<F: FloatBits + Copy>(float: F) -> F {
let bits = float.to_bits();
if float.float_is_nan() || bits == F::infinity().to_bits() {
return float;
}
// Special case: -0.0 → +0.0
if bits == F::NEG_ZERO {
return F::from_bits(F::ZERO);
}
...
```
```rust
pub fn next_down<F: FloatBits + Copy>(float: F) -> F {
let bits = float.to_bits();
if float.float_is_nan() || bits == F::neg_infinity().to_bits() {
return float;
}
// Special case: +0.0 → -0.0
if bits == F::ZERO {
return F::from_bits(F::NEG_ZERO);
}
...
```
With these changes, the interval calculations now respect the special ±0.0
representations before moving into the subnormal range. This aligns the
rounding behavior with how ScalarValue comparisons already work and avoids
producing unexpected intervals.
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