devanshu0987 commented on code in PR #20099:
URL: https://github.com/apache/datafusion/pull/20099#discussion_r2754526208
##########
datafusion/functions/src/math/floor.rs:
##########
@@ -310,9 +351,45 @@ fn int_preimage_bounds<I: CheckedAdd + One + Copy>(n: I)
-> Option<(I, I)> {
Some((n, upper))
}
+/// Compute preimage bounds for floor function on decimal types.
+/// For floor(x) = n, the preimage is [n, n+1).
+/// Returns None if:
+/// - The value has a fractional part (floor always returns integers)
+/// - Adding 1 would overflow
+fn decimal_preimage_bounds<D: DecimalType>(
+ value: D::Native,
+ precision: u8,
+ scale: i8,
+) -> Option<(D::Native, D::Native)>
+where
+ D::Native: DecimalCast + ArrowNativeTypeOp + std::ops::Rem<Output =
D::Native>,
+{
+ // Use rescale_decimal to compute "1" at target scale (avoids manual pow)
+ // Convert integer 1 (scale=0) to the target scale
+ let one_scaled: D::Native = rescale_decimal::<D, D>(
+ D::Native::ONE, // value = 1
+ 1, // input_precision = 1
+ 0, // input_scale = 0 (integer)
+ precision, // output_precision
+ scale, // output_scale
+ )?;
+
+ // floor always returns an integer, so if value has a fractional part,
there's no solution
+ // Check: value % one_scaled != 0 means fractional part exists
+ if scale > 0 && value % one_scaled != D::Native::ZERO {
Review Comment:
Hi, the logic here come from the idea that `floor(x) = 1.3` has no pre-image
solution. We do not want to optimize it via this.
floor(x) will always return a floor data type but it will actually be an
integer.
```
// floor always returns an integer, so if n has a fractional part,
there's no solution
if n.fract() != F::zero() {
return None;
}
```
Same logic is carried over here for Decimal.
`scale <= 0` is effectively an integer and hence only possibility is to
check for overflow which we check in the next line.
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