Add from_timestamp_nanos (chronotope#1357)

* Add from_timestamp_nanos

Add and implement from_timestamp_nanos and add unit test for it

* Fix lint check error

* Add pub(crate) for NANOS_PER_SEC

* Replace number with constant variable

src/duration.rs

@@ -24,7 +24,7 @@ const NANOS_PER_MICRO: i32 = 1000;
 /// The number of nanoseconds in a millisecond.
 const NANOS_PER_MILLI: i32 = 1_000_000;
 /// The number of nanoseconds in seconds.
-const NANOS_PER_SEC: i32 = 1_000_000_000;
+pub(crate) const NANOS_PER_SEC: i32 = 1_000_000_000;
 /// The number of microseconds per second.
 const MICROS_PER_SEC: i64 = 1_000_000;
 /// The number of milliseconds per second.

src/naive/datetime/mod.rs

@@ -13,7 +13,7 @@ use core::{fmt, str};
 #[cfg(feature = "rkyv")]
 use rkyv::{Archive, Deserialize, Serialize};
 
-use crate::duration::Duration as OldDuration;
+use crate::duration::{Duration as OldDuration, NANOS_PER_SEC};
 #[cfg(feature = "alloc")]
 use crate::format::DelayedFormat;
 use crate::format::{parse, parse_and_remainder, ParseError, ParseResult, Parsed, StrftimeItems};
@@ -197,6 +197,39 @@ impl NaiveDateTime {
         NaiveDateTime::from_timestamp_opt(secs, nsecs)
     }
 
+    /// Creates a new [NaiveDateTime] from nanoseconds since the UNIX epoch.
+    ///
+    /// The UNIX epoch starts on midnight, January 1, 1970, UTC.
+    ///
+    /// # Errors
+    ///
+    /// Returns `None` if the number of nanoseconds would be out of range for a `NaiveDateTime`
+    /// (more than ca. 262,000 years away from common era)
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use chrono::NaiveDateTime;
+    /// let timestamp_nanos: i64 = 1662921288_000_000_000; //Sunday, September 11, 2022 6:34:48 PM
+    /// let naive_datetime = NaiveDateTime::from_timestamp_nanos(timestamp_nanos);
+    /// assert!(naive_datetime.is_some());
+    /// assert_eq!(timestamp_nanos, naive_datetime.unwrap().timestamp_nanos_opt().unwrap());
+    ///
+    /// // Negative timestamps (before the UNIX epoch) are supported as well.
+    /// let timestamp_nanos: i64 = -2208936075_000_000_000; //Mon Jan 01 1900 14:38:45 GMT+0000
+    /// let naive_datetime = NaiveDateTime::from_timestamp_nanos(timestamp_nanos);
+    /// assert!(naive_datetime.is_some());
+    /// assert_eq!(timestamp_nanos, naive_datetime.unwrap().timestamp_nanos_opt().unwrap());
+    /// ```
+    #[inline]
+    #[must_use]
+    pub const fn from_timestamp_nanos(nanos: i64) -> Option<NaiveDateTime> {
+        let secs = nanos.div_euclid(NANOS_PER_SEC as i64);
+        let nsecs = nanos.rem_euclid(NANOS_PER_SEC as i64) as u32;
+
+        NaiveDateTime::from_timestamp_opt(secs, nsecs)
+    }
+
     /// Makes a new `NaiveDateTime` corresponding to a UTC date and time,
     /// from the number of non-leap seconds
     /// since the midnight UTC on January 1, 1970 (aka "UNIX timestamp")

src/naive/datetime/tests.rs

@@ -78,6 +78,57 @@ fn test_datetime_from_timestamp_micros() {
     }
 }
 
+#[test]
+fn test_datetime_from_timestamp_nanos() {
+    let valid_map = [
+        (1662921288000000000, "2022-09-11 18:34:48.000000000"),
+        (1662921288123456000, "2022-09-11 18:34:48.123456000"),
+        (1662921288123456789, "2022-09-11 18:34:48.123456789"),
+        (1662921287890000000, "2022-09-11 18:34:47.890000000"),
+        (-2208936075000000000, "1900-01-01 14:38:45.000000000"),
+        (-5337182663000000000, "1800-11-15 01:15:37.000000000"),
+        (0, "1970-01-01 00:00:00.000000000"),
+        (119731017000000000, "1973-10-17 18:36:57.000000000"),
+        (1234567890000000000, "2009-02-13 23:31:30.000000000"),
+        (2034061609000000000, "2034-06-16 09:06:49.000000000"),
+    ];
+
+    for (timestamp_nanos, _formatted) in valid_map.iter().copied() {
+        let naive_datetime = NaiveDateTime::from_timestamp_nanos(timestamp_nanos).unwrap();
+        assert_eq!(timestamp_nanos, naive_datetime.timestamp_nanos_opt().unwrap());
+        #[cfg(feature = "alloc")]
+        assert_eq!(naive_datetime.format("%F %T%.9f").to_string(), _formatted);
+    }
+
+    const A_BILLION: i64 = 1_000_000_000;
+    // Maximum datetime in nanoseconds
+    let maximum = "2262-04-11T23:47:16.854775804";
+    let parsed: NaiveDateTime = maximum.parse().unwrap();
+    let nanos = parsed.timestamp_nanos_opt().unwrap();
+    assert_eq!(
+        NaiveDateTime::from_timestamp_nanos(nanos).unwrap(),
+        NaiveDateTime::from_timestamp_opt(nanos / A_BILLION, (nanos % A_BILLION) as u32).unwrap()
+    );
+    // Minimum datetime in nanoseconds
+    let minimum = "1677-09-21T00:12:44.000000000";
+    let parsed: NaiveDateTime = minimum.parse().unwrap();
+    let nanos = parsed.timestamp_nanos_opt().unwrap();
+    assert_eq!(
+        NaiveDateTime::from_timestamp_nanos(nanos).unwrap(),
+        NaiveDateTime::from_timestamp_opt(nanos / A_BILLION, (nanos % A_BILLION) as u32).unwrap()
+    );
+
+    // Test that the result of `from_timestamp_nanos` compares equal to
+    // that of `from_timestamp_opt`.
+    let secs_test = [0, 1, 2, 1000, 1234, 12345678, -1, -2, -1000, -12345678];
+    for secs in secs_test.iter().copied() {
+        assert_eq!(
+            NaiveDateTime::from_timestamp_nanos(secs * 1_000_000_000),
+            NaiveDateTime::from_timestamp_opt(secs, 0)
+        );
+    }
+}
+
 #[test]
 fn test_datetime_from_timestamp() {
     let from_timestamp = |secs| NaiveDateTime::from_timestamp_opt(secs, 0);