Jefffrey commented on code in PR #10409:
URL: https://github.com/apache/arrow-rs/pull/10409#discussion_r3705129824
##########
arrow-arith/src/numeric.rs:
##########
@@ -724,6 +729,125 @@ fn interval_mul_op<T: IntervalOp>(
))
}
+/// Multiplies an `IntervalMonthDayNano` by an `f64`, mirroring DuckDB's
+/// `interval_t` layout of months, days, and a sub-day component (nanoseconds
in
+/// Arrow, microseconds in DuckDB).
+///
<https://github.com/duckdb/duckdb/blob/21aca0424f1faf78b593b1e6fbfdd4846624c987/src/include/duckdb/common/types/interval.hpp#L24-L27>
+///
+/// Algorithm:
+///
+/// 1. use checked integer multiplication when `factor` fits in `i64` (early
return).
+/// 2. multiply months and days separately and truncate floating point.
Review Comment:
```suggestion
/// 2. multiply months and days separately
```
I dont think we truncate until the nanosecond precision, unless I'm mistaken
##########
arrow-arith/src/numeric.rs:
##########
@@ -724,6 +729,125 @@ fn interval_mul_op<T: IntervalOp>(
))
}
+/// Multiplies an `IntervalMonthDayNano` by an `f64`, mirroring DuckDB's
+/// `interval_t` layout of months, days, and a sub-day component (nanoseconds
in
+/// Arrow, microseconds in DuckDB).
+///
<https://github.com/duckdb/duckdb/blob/21aca0424f1faf78b593b1e6fbfdd4846624c987/src/include/duckdb/common/types/interval.hpp#L24-L27>
+///
+/// Algorithm:
+///
+/// 1. use checked integer multiplication when `factor` fits in `i64` (early
return).
+/// 2. multiply months and days separately and truncate floating point.
+/// 3. cascade remainders: convert fractional months to days using 30
+/// days per month, then fractional days to a sub-day value using 24 hours
+/// per day.
+/// 4. combine the cascaded remainder with the scaled input nanoseconds and
round ties-to-even at nanosecond precision.
+/// 5. return an overflow error if any output component is out of
+/// range.
+fn interval_mul_f64(
+ interval: IntervalMonthDayNano,
+ factor: f64,
+) -> Result<IntervalMonthDayNano, ArrowError> {
+ const DAYS_PER_MONTH: f64 = 30.;
+ const NANOS_PER_SECOND: f64 = NANOSECONDS as f64;
+ const SECONDS_PER_DAY: f64 = SECONDS_IN_DAY as f64;
+
+ // Keep integral factors exact instead of round-tripping i64 nanoseconds
through f64.
+ if factor.fract() == 0. {
+ if let Some(factor) = ToPrimitive::to_i64(&factor) {
+ return IntervalMonthDayNanoType::mul_i64(interval, factor);
+ }
+ }
+
+ // Based on DuckDB's INTERVAL * DOUBLE implementation, which is referenced
from PostgreSQL's interval_mul:
+ //
https://github.com/duckdb/duckdb/blob/21aca0424f1faf78b593b1e6fbfdd4846624c987/src/function/scalar/operator/multiply.cpp#L48-L123
+ // PostgreSQL's interval_mul:
+ //
https://github.com/postgres/postgres/blob/78758d37306cd89ab060f00cb06f249018d5b8da/src/backend/utils/adt/timestamp.c#L3627-L3744
+ let overflow =
+ |component| ArrowError::ArithmeticOverflow(format!("Overflow in
interval {component}"));
+ let timestamp_round =
+ |value: f64| (value * NANOS_PER_SECOND).round_ties_even() /
NANOS_PER_SECOND;
+
+ let months_product = f64::from(interval.months) * factor;
+ if !months_product.is_finite()
+ || months_product < f64::from(i32::MIN)
+ || months_product > f64::from(i32::MAX)
+ {
+ return Err(overflow("months"));
+ }
+ let months = months_product.to_i32().ok_or_else(|| overflow("months"))?;
+
+ let days_product = f64::from(interval.days) * factor;
+ if !days_product.is_finite()
+ || days_product < f64::from(i32::MIN)
+ || days_product > f64::from(i32::MAX)
+ {
+ return Err(overflow("days"));
+ }
+ let mut days = days_product.to_i32().ok_or_else(|| overflow("days"))?;
+
+ let month_remainder = timestamp_round(months_product.fract() *
DAYS_PER_MONTH);
+ let month_remainder_days = month_remainder
+ .to_i32()
+ .ok_or_else(|| overflow("month remainder"))?;
+ let mut seconds_remainder = timestamp_round(
+ (days_product - f64::from(days) + month_remainder -
f64::from(month_remainder_days))
Review Comment:
can use `fract()` here too I believe, on both days & month
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