Add TimeDelta::checked_mul and TimeDelta::checked_div

src/time_delta.rs

@@ -372,6 +372,40 @@ impl TimeDelta {
         TimeDelta::new(secs, nanos as u32)
     }
 
+    /// Multiply a `TimeDelta` with a i32, returning `None` if overflow occurred.
+    #[must_use]
+    pub const fn checked_mul(&self, rhs: i32) -> Option<TimeDelta> {
+        // Multiply nanoseconds as i64, because it cannot overflow that way.
+        let total_nanos = self.nanos as i64 * rhs as i64;
+        let (extra_secs, nanos) = div_mod_floor_64(total_nanos, NANOS_PER_SEC as i64);
+        // Multiply seconds as i128 to prevent overflow
+        let secs: i128 = self.secs as i128 * rhs as i128 + extra_secs as i128;
+        if secs <= i64::MIN as i128 || secs >= i64::MAX as i128 {
+            return None;
+        };
+        Some(TimeDelta { secs: secs as i64, nanos: nanos as i32 })
+    }
+
+    /// Divide a `TimeDelta` with a i32, returning `None` if dividing by 0.
+    #[must_use]
+    pub const fn checked_div(&self, rhs: i32) -> Option<TimeDelta> {
+        if rhs == 0 {
+            return None;
+        }
+        let secs = self.secs / rhs as i64;
+        let carry = self.secs % rhs as i64;
+        let extra_nanos = carry * NANOS_PER_SEC as i64 / rhs as i64;
+        let nanos = self.nanos / rhs + extra_nanos as i32;
+
+        let (secs, nanos) = match nanos {
+            i32::MIN..=-1 => (secs - 1, nanos + NANOS_PER_SEC),
+            NANOS_PER_SEC..=i32::MAX => (secs + 1, nanos - NANOS_PER_SEC),
+            _ => (secs, nanos),
+        };
+
+        Some(TimeDelta { secs, nanos })
+    }
+
     /// Returns the `TimeDelta` as an absolute (non-negative) value.
     #[inline]
     pub const fn abs(&self) -> TimeDelta {
@@ -489,31 +523,15 @@ impl Mul<i32> for TimeDelta {
     type Output = TimeDelta;
 
     fn mul(self, rhs: i32) -> TimeDelta {
-        // Multiply nanoseconds as i64, because it cannot overflow that way.
-        let total_nanos = self.nanos as i64 * rhs as i64;
-        let (extra_secs, nanos) = div_mod_floor_64(total_nanos, NANOS_PER_SEC as i64);
-        let secs = self.secs * rhs as i64 + extra_secs;
-        TimeDelta { secs, nanos: nanos as i32 }
+        self.checked_mul(rhs).expect("`TimeDelta * i32` overflowed")
     }
 }
 
 impl Div<i32> for TimeDelta {
     type Output = TimeDelta;
 
     fn div(self, rhs: i32) -> TimeDelta {
-        let mut secs = self.secs / rhs as i64;
-        let carry = self.secs - secs * rhs as i64;
-        let extra_nanos = carry * NANOS_PER_SEC as i64 / rhs as i64;
-        let mut nanos = self.nanos / rhs + extra_nanos as i32;
-        if nanos >= NANOS_PER_SEC {
-            nanos -= NANOS_PER_SEC;
-            secs += 1;
-        }
-        if nanos < 0 {
-            nanos += NANOS_PER_SEC;
-            secs -= 1;
-        }
-        TimeDelta { secs, nanos }
+        self.checked_div(rhs).expect("`i32` is zero")
     }
 }
 
@@ -1034,6 +1052,7 @@ mod tests {
     #[test]
     fn test_duration_checked_ops() {
         let milliseconds = |ms| TimeDelta::try_milliseconds(ms).unwrap();
+        let seconds = |s| TimeDelta::try_seconds(s).unwrap();
 
         assert_eq!(
             milliseconds(i64::MAX).checked_add(&milliseconds(0)),
@@ -1056,6 +1075,10 @@ mod tests {
         );
         assert!(milliseconds(-i64::MAX).checked_sub(&milliseconds(1)).is_none());
         assert!(milliseconds(-i64::MAX).checked_sub(&TimeDelta::nanoseconds(1)).is_none());
+
+        assert!(seconds(i64::MAX / 1000).checked_mul(2000).is_none());
+        assert!(seconds(i64::MIN / 1000).checked_mul(2000).is_none());
+        assert!(seconds(1).checked_div(0).is_none());
     }
 
     #[test]