Add tests and handling for negative timestamps

src/lib.rs

@@ -871,7 +871,16 @@ pub trait Datelike: Sized {
     /// Returns `None` when the resulting value would be invalid.
     fn with_ordinal0(&self, ordinal0: u32) -> Option<Self>;
 
-    /// Returns the number of days since January 1, 1 (Day 1) in the proleptic Gregorian calendar.
+    /// Returns the number of days since January 1, Year 1 (aka Day 1) in the
+    /// proleptic Gregorian calendar.
+    ///
+    /// # Example:
+    ///
+    /// ~~~
+    /// use chrono::{NaiveDate, Datelike};
+    /// assert_eq!(NaiveDate::from_ymd(1970, 1, 1).num_days_from_ce(), 719163);
+    /// assert_eq!(NaiveDate::from_ymd(0, 1, 1).num_days_from_ce(), -365);
+    /// ~~~
     fn num_days_from_ce(&self) -> i32 {
         // we know this wouldn't overflow since year is limited to 1/2^13 of i32's full range.
         let mut year = self.year() - 1;

src/naive/datetime.rs

@@ -255,12 +255,19 @@ impl NaiveDateTime {
     ///
     /// let dt = NaiveDate::from_ymd(2001, 9, 9).and_hms(1, 46, 40);
     /// assert_eq!(dt.timestamp(), 1_000_000_000);
+    ///
+    /// let dt = NaiveDate::from_ymd(1969, 12, 31).and_hms(23, 59, 59);
+    /// assert_eq!(dt.timestamp(), -1);
+    ///
+    /// let dt = NaiveDate::from_ymd(-1, 1, 1).and_hms(0, 0, 0);
+    /// assert_eq!(dt.timestamp(), -62198755200);
     /// ~~~~
     #[inline]
     pub fn timestamp(&self) -> i64 {
-        let ndays = i64::from(self.date.num_days_from_ce());
-        let nseconds = i64::from(self.time.num_seconds_from_midnight());
-        (ndays - 719_163) * 86_400 + nseconds
+        const UNIX_EPOCH_DAY: i64 = 719_163;
+        let gregorian_day = i64::from(self.date.num_days_from_ce());
+        let seconds_from_midnight = i64::from(self.time.num_seconds_from_midnight());
+        (gregorian_day - UNIX_EPOCH_DAY) * 86_400 + seconds_from_midnight
     }
 
     /// Returns the number of non-leap *milliseconds* since midnight on January 1, 1970.
@@ -283,6 +290,9 @@ impl NaiveDateTime {
     ///
     /// let dt = NaiveDate::from_ymd(2001, 9, 9).and_hms_milli(1, 46, 40, 555);
     /// assert_eq!(dt.timestamp_millis(), 1_000_000_000_555);
+    ///
+    /// let dt = NaiveDate::from_ymd(1969, 12, 31).and_hms_milli(23, 59, 59, 100);
+    /// assert_eq!(dt.timestamp_millis(), -900);
     /// ~~~~
     #[inline]
     pub fn timestamp_millis(&self) -> i64 {

src/naive/internals.rs

@@ -475,7 +475,7 @@ mod tests {
     use Weekday;
     use super::{Of, Mdf};
     use super::{YearFlags, A, B, C, D, E, F, G, AG, BA, CB, DC, ED, FE, GF};
-    use num_iter::range_inclusive;
+    use self::num_iter::range_inclusive;
     use std::u32;
 
     const NONLEAP_FLAGS: [YearFlags; 7] = [A, B, C, D, E, F, G];