From bddfbf8d94708f93760b8b55ede09b927515de5c Mon Sep 17 00:00:00 2001
From: Paul Dicker <pitdicker@gmail.com>
Date: Sat, 22 Apr 2023 08:11:05 +0200
Subject: [PATCH] Simplify from_timestamp_millis, from_timestamp_micros

---
 src/naive/datetime/mod.rs | 71 ++++-----------------------------------
 1 file changed, 6 insertions(+), 65 deletions(-)

diff --git a/src/naive/datetime/mod.rs b/src/naive/datetime/mod.rs
index d13ff99889..659d4dd87d 100644
--- a/src/naive/datetime/mod.rs
+++ b/src/naive/datetime/mod.rs
@@ -5,7 +5,6 @@
 
 #[cfg(any(feature = "alloc", feature = "std", test))]
 use core::borrow::Borrow;
-use core::convert::TryFrom;
 use core::fmt::Write;
 use core::ops::{Add, AddAssign, Sub, SubAssign};
 use core::{fmt, str};
@@ -22,7 +21,6 @@ use crate::format::{Fixed, Item, Numeric, Pad};
 use crate::naive::{Days, IsoWeek, NaiveDate, NaiveTime};
 use crate::oldtime::Duration as OldDuration;
 use crate::{DateTime, Datelike, LocalResult, Months, TimeZone, Timelike, Weekday};
-use core::cmp::Ordering;
 
 #[cfg(feature = "rustc-serialize")]
 pub(super) mod rustc_serialize;
@@ -42,11 +40,6 @@ mod tests;
 /// touching that call when we are already sure that it WILL overflow...
 const MAX_SECS_BITS: usize = 44;
 
-/// Number of nanoseconds in a millisecond
-const NANOS_IN_MILLISECOND: u32 = 1_000_000;
-/// Number of nanoseconds in a second
-const NANOS_IN_SECOND: u32 = 1000 * NANOS_IN_MILLISECOND;
-
 /// The minimum possible `NaiveDateTime`.
 #[deprecated(since = "0.4.20", note = "Use NaiveDateTime::MIN instead")]
 pub const MIN_DATETIME: NaiveDateTime = NaiveDateTime::MIN;
@@ -87,32 +80,6 @@ pub struct NaiveDateTime {
     time: NaiveTime,
 }
 
-/// The unit of a timestamp expressed in fractions of a second.
-/// Currently either milliseconds or microseconds.
-///
-/// This is a private type, used in the implementation of
-/// [NaiveDateTime::from_timestamp_millis] and [NaiveDateTime::from_timestamp_micros].
-#[derive(Clone, Copy, Debug)]
-enum TimestampUnit {
-    Millis,
-    Micros,
-}
-
-impl TimestampUnit {
-    fn per_second(self) -> u32 {
-        match self {
-            TimestampUnit::Millis => 1_000,
-            TimestampUnit::Micros => 1_000_000,
-        }
-    }
-    fn nanos_per(self) -> u32 {
-        match self {
-            TimestampUnit::Millis => 1_000_000,
-            TimestampUnit::Micros => 1_000,
-        }
-    }
-}
-
 impl NaiveDateTime {
     /// Makes a new `NaiveDateTime` from date and time components.
     /// Equivalent to [`date.and_time(time)`](./struct.NaiveDate.html#method.and_time)
@@ -180,7 +147,9 @@ impl NaiveDateTime {
     #[inline]
     #[must_use]
     pub fn from_timestamp_millis(millis: i64) -> Option<NaiveDateTime> {
-        Self::from_timestamp_unit(millis, TimestampUnit::Millis)
+        let secs = millis.div_euclid(1000);
+        let nsecs = millis.rem_euclid(1000) as u32 * 1_000_000;
+        NaiveDateTime::from_timestamp_opt(secs, nsecs)
     }
 
     /// Creates a new [NaiveDateTime] from microseconds since the UNIX epoch.
@@ -207,7 +176,9 @@ impl NaiveDateTime {
     #[inline]
     #[must_use]
     pub fn from_timestamp_micros(micros: i64) -> Option<NaiveDateTime> {
-        Self::from_timestamp_unit(micros, TimestampUnit::Micros)
+        let secs = micros.div_euclid(1_000_000);
+        let nsecs = micros.rem_euclid(1_000_000) as u32 * 1000;
+        NaiveDateTime::from_timestamp_opt(secs, nsecs)
     }
 
     /// Makes a new `NaiveDateTime` corresponding to a UTC date and time,
@@ -950,36 +921,6 @@ impl NaiveDateTime {
     pub const MIN: Self = Self { date: NaiveDate::MIN, time: NaiveTime::MIN };
     /// The maximum possible `NaiveDateTime`.
     pub const MAX: Self = Self { date: NaiveDate::MAX, time: NaiveTime::MAX };
-
-    /// Creates a new [NaiveDateTime] from milliseconds or microseconds since the UNIX epoch.
-    ///
-    /// This is a private function used by [from_timestamp_millis] and [from_timestamp_micros].
-    #[inline]
-    fn from_timestamp_unit(value: i64, unit: TimestampUnit) -> Option<NaiveDateTime> {
-        let (secs, subsecs) =
-            (value / i64::from(unit.per_second()), value % i64::from(unit.per_second()));
-
-        match subsecs.cmp(&0) {
-            Ordering::Less => {
-                // in the case where our subsec part is negative, then we are actually in the earlier second
-                // hence we subtract one from the seconds part, and we then add a whole second worth of nanos
-                // to our nanos part. Due to the use of u32 datatype, it is more convenient to subtract
-                // the absolute value of the subsec nanos from a whole second worth of nanos
-                let nsecs = u32::try_from(subsecs.abs()).ok()? * unit.nanos_per();
-                NaiveDateTime::from_timestamp_opt(
-                    secs.checked_sub(1)?,
-                    NANOS_IN_SECOND.checked_sub(nsecs)?,
-                )
-            }
-            Ordering::Equal => NaiveDateTime::from_timestamp_opt(secs, 0),
-            Ordering::Greater => {
-                // convert the subsec millis into nanosecond scale so they can be supplied
-                // as the nanoseconds parameter
-                let nsecs = u32::try_from(subsecs).ok()? * unit.nanos_per();
-                NaiveDateTime::from_timestamp_opt(secs, nsecs)
-            }
-        }
-    }
 }
 
 impl Datelike for NaiveDateTime {