fix millisecond fraction being handled with wrong scale

src/date.rs

@@ -56,7 +56,7 @@ impl FromStr for Date {
 
 // 2e10 if greater than this, the number is in ms, if less than or equal, it's in seconds
 // (in seconds this is 11th October 2603, in ms it's 20th August 1970)
-const MS_WATERSHED: i64 = 20_000_000_000;
+pub(crate) const MS_WATERSHED: i64 = 20_000_000_000;
 // 1600-01-01 as a unix timestamp used for from_timestamp below
 const UNIX_1600: i64 = -11_676_096_000;
 // 9999-12-31T23:59:59 as a unix timestamp, used as max allowed value below
@@ -206,9 +206,13 @@ impl Date {
     /// assert_eq!(d.to_string(), "2022-06-07");
     /// ```
     pub fn from_timestamp(timestamp: i64, require_exact: bool) -> Result<Self, ParseError> {
-        let (timestamp_second, _) = Self::timestamp_watershed(timestamp)?;
+        let (timestamp_second, millis) = Self::timestamp_watershed(timestamp)?;
         let d = Self::from_timestamp_calc(timestamp_second)?;
         if require_exact {
+            if millis != 0 {
+                return Err(ParseError::DateNotExact);
+            }
+
             let time_second = timestamp_second.rem_euclid(86_400);
             if time_second != 0 {
                 return Err(ParseError::DateNotExact);
@@ -275,11 +279,11 @@ impl Date {
 
     pub(crate) fn timestamp_watershed(timestamp: i64) -> Result<(i64, u32), ParseError> {
         let ts_abs = timestamp.checked_abs().ok_or(ParseError::DateTooSmall)?;
-        let (mut seconds, mut microseconds) = if ts_abs > MS_WATERSHED {
-            (timestamp / 1_000, timestamp % 1_000 * 1000)
-        } else {
-            (timestamp, 0)
-        };
+        if ts_abs <= MS_WATERSHED {
+            return Ok((timestamp, 0));
+        }
+        let mut seconds = timestamp / 1_000;
+        let mut microseconds = ((timestamp % 1_000) * 1000) as i32;
         if microseconds < 0 {
             seconds -= 1;
             microseconds += 1_000_000;

src/datetime.rs

@@ -1,5 +1,5 @@
-use crate::numbers::{float_parse_bytes, IntFloat};
-use crate::TimeConfigBuilder;
+use crate::date::MS_WATERSHED;
+use crate::{int_parse_bytes, TimeConfigBuilder};
 use crate::{time::TimeConfig, Date, ParseError, Time};
 use std::cmp::Ordering;
 use std::fmt;
@@ -339,14 +339,36 @@ impl DateTime {
     pub fn parse_bytes_with_config(bytes: &[u8], config: &TimeConfig) -> Result<Self, ParseError> {
         match Self::parse_bytes_rfc3339_with_config(bytes, config) {
             Ok(d) => Ok(d),
-            Err(e) => match float_parse_bytes(bytes) {
-                IntFloat::Int(int) => Self::from_timestamp_with_config(int, 0, config),
-                IntFloat::Float(float) => {
-                    let micro = (float.fract() * 1_000_000_f64).round() as u32;
-                    Self::from_timestamp_with_config(float.floor() as i64, micro, config)
+            Err(e) => {
+                let mut split = bytes.splitn(2, |&b| b == b'.');
+                let Some(timestamp) =
+                    int_parse_bytes(split.next().expect("splitn always returns at least one element"))
+                else {
+                    return Err(e);
+                };
+                let float_fraction = split.next();
+                debug_assert!(split.next().is_none()); // at most two elements
+                match float_fraction {
+                    Some(fract) => {
+                        // fraction is either:
+                        // - up to 3 digits of millisecond fractions, i.e. microseconds
+                        // - or up to 6 digits of second fractions, i.e. milliseconds
+                        let max_digits = if timestamp > MS_WATERSHED { 3 } else { 6 };
+                        let Some(fract_integers) = int_parse_bytes(fract) else {
+                            return Err(e);
+                        };
+                        let multiple = 10f64.powf(max_digits as f64 - fract.len() as f64);
+                        Self::from_timestamp_with_config(
+                            timestamp,
+                            // FIXME should we error if the fraction is too long?
+                            // We have TimeConfig truncate / error option.
+                            (fract_integers as f64 * multiple).round() as u32,
+                            config,
+                        )
+                    }
+                    None => Self::from_timestamp_with_config(timestamp, 0, config),
                 }
-                IntFloat::Err => Err(e),
-            },
+            }
         }
     }