Fix rounding of negative hour transform (#1128)

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Author: Fokko

bindings/python/tests/test_transform.py

@@ -90,9 +90,15 @@ def test_day_transform():
 
 
 def test_hour_transform():
-    arr = pa.array([datetime(1970, 1, 1, 19, 1, 23), datetime(2000, 3, 1, 12, 1, 23)])
+    arr = pa.array(
+        [
+            datetime(1970, 1, 1, 19, 1, 23),
+            datetime(2000, 3, 1, 12, 1, 23),
+            datetime(22, 5, 1, 22, 1, 1),  # Negative
+        ]
+    )
     result = transform.hour(arr)
-    expected = pa.array([19, 264420], type=pa.int32())
+    expected = pa.array([19, 264420, -17072905], type=pa.int32())
     assert result == expected
 
 

crates/iceberg/src/transform/temporal.rs

@@ -30,8 +30,10 @@ use super::TransformFunction;
 use crate::spec::{Datum, PrimitiveLiteral, PrimitiveType};
 use crate::{Error, ErrorKind, Result};
 
-/// Hour in one second.
-const HOUR_PER_SECOND: f64 = 1.0_f64 / 3600.0_f64;
+/// Microseconds in one hour.
+const MICROSECONDS_PER_HOUR: i64 = 3_600_000_000;
+/// Nanoseconds in one hour.
+const NANOSECONDS_PER_HOUR: i64 = 3_600_000_000_000;
 /// Year of unix epoch.
 const UNIX_EPOCH_YEAR: i32 = 1970;
 /// One second in micros.
@@ -335,12 +337,12 @@ pub struct Hour;
 impl Hour {
     #[inline]
     fn hour_timestamp_micro(v: i64) -> i32 {
-        (v as f64 / 1000.0 / 1000.0 * HOUR_PER_SECOND) as i32
+        (v / MICROSECONDS_PER_HOUR) as i32
     }
 
     #[inline]
     fn hour_timestamp_nano(v: i64) -> i32 {
-        (v as f64 / 1_000_000.0 / 1000.0 * HOUR_PER_SECOND) as i32
+        (v / NANOSECONDS_PER_HOUR) as i32
     }
 }
 
@@ -2761,9 +2763,11 @@ mod test {
         // Test TimestampMicrosecond
         test_timestamp_and_tz_transform("2017-12-01 18:00:00.00", &hour, Datum::int(420042));
         test_timestamp_and_tz_transform("1969-12-31 23:00:00.00", &hour, Datum::int(-1));
+        test_timestamp_and_tz_transform("0022-05-01 22:01:01.00", &hour, Datum::int(-17072905));
 
         // Test TimestampNanosecond
         test_timestamp_ns_and_tz_transform("2017-12-01 18:00:00.00", &hour, Datum::int(420042));
         test_timestamp_ns_and_tz_transform("1969-12-31 23:00:00.00", &hour, Datum::int(-1));
+        test_timestamp_ns_and_tz_transform("1900-05-01 22:01:01.00", &hour, Datum::int(-610705));
     }
 }