Add SubSecondRound extension trait with impl for Timelike
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@ -409,6 +409,7 @@ pub use date::{Date, MIN_DATE, MAX_DATE};
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pub use datetime::{DateTime, SecondsFormat};
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pub use datetime::{DateTime, SecondsFormat};
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#[cfg(feature = "rustc-serialize")] pub use datetime::rustc_serialize::TsSeconds;
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#[cfg(feature = "rustc-serialize")] pub use datetime::rustc_serialize::TsSeconds;
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pub use format::{ParseError, ParseResult};
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pub use format::{ParseError, ParseResult};
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pub use round::SubSecondRound;
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/// A convenience module appropriate for glob imports (`use chrono::prelude::*;`).
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/// A convenience module appropriate for glob imports (`use chrono::prelude::*;`).
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pub mod prelude {
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pub mod prelude {
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@ -418,6 +419,7 @@ pub mod prelude {
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#[doc(no_inline)] pub use {NaiveDate, NaiveTime, NaiveDateTime};
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#[doc(no_inline)] pub use {NaiveDate, NaiveTime, NaiveDateTime};
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#[doc(no_inline)] pub use Date;
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#[doc(no_inline)] pub use Date;
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#[doc(no_inline)] pub use {DateTime, SecondsFormat};
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#[doc(no_inline)] pub use {DateTime, SecondsFormat};
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#[doc(no_inline)] pub use {SubSecondRound};
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}
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}
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// useful throughout the codebase
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// useful throughout the codebase
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@ -464,6 +466,7 @@ pub mod naive {
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mod date;
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mod date;
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mod datetime;
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mod datetime;
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pub mod format;
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pub mod format;
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mod round;
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/// Serialization/Deserialization in alternate formats
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/// Serialization/Deserialization in alternate formats
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///
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///
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@ -0,0 +1,162 @@
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// This is a part of Chrono.
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// See README.md and LICENSE.txt for details.
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use Timelike;
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use std::ops::{Add, Sub};
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use oldtime::Duration;
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/// Extension trait for subsecond rounding or truncation to a maximum number
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/// of digits. Rounding can be used to decrease the error variance when
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/// serializing/persisting to lower precision. Truncation is the default
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/// behavior in Chrono display formatting. Either can be used to guarantee
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/// equality (e.g. for testing) when round-tripping through a lower precision
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/// format.
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pub trait SubSecondRound {
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/// Return a copy rounded to the specified number of subsecond digits. With
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/// 9 or more digits, self is returned unmodified. Halfway values are
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/// rounded up (away from zero).
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fn round(self, digits: u16) -> Self;
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/// Return a copy truncated to the specified number of subsecond
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/// digits. With 9 or more digits, self is returned unmodified.
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fn trunc(self, digits: u16) -> Self;
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}
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impl<T> SubSecondRound for T
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where T: Timelike + Add<Duration, Output=T> + Sub<Duration, Output=T>
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{
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fn round(self, digits: u16) -> T {
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let span = span_for_digits(digits);
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let rem = self.nanosecond() % span;
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if rem > 0 {
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let rev = span - rem;
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if rev <= rem {
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self + Duration::nanoseconds(rev.into()) // up
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} else {
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self - Duration::nanoseconds(rem.into()) // down
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}
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} else {
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self // unchanged
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}
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}
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fn trunc(self, digits: u16) -> T {
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let span = span_for_digits(digits);
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let rem = self.nanosecond() % span;
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if rem > 0 {
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self - Duration::nanoseconds(rem.into()) // truncate
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} else {
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self // unchanged
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}
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}
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}
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// Return the maximum span in nanoseconds for the target number of digits.
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fn span_for_digits(digits: u16) -> u32 {
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// fast lookup form of: 10^(9-min(9,digits))
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match digits {
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0 => 1_000_000_000,
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1 => 100_000_000,
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2 => 10_000_000,
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3 => 1_000_000,
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4 => 100_000,
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5 => 10_000,
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6 => 1_000,
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7 => 100,
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8 => 10,
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_ => 1
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}
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}
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#[cfg(test)]
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mod tests {
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use Timelike;
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use offset::{FixedOffset, TimeZone, Utc};
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use super::SubSecondRound;
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#[test]
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fn test_round() {
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let pst = FixedOffset::east(8 * 60 * 60);
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let dt = pst.ymd(2018, 1, 11).and_hms_nano(10, 5, 13, 084_660_684);
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assert_eq!(dt.round(10), dt);
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assert_eq!(dt.round(9), dt);
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assert_eq!(dt.round(8).nanosecond(), 084_660_680);
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assert_eq!(dt.round(7).nanosecond(), 084_660_700);
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assert_eq!(dt.round(6).nanosecond(), 084_661_000);
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assert_eq!(dt.round(5).nanosecond(), 084_660_000);
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assert_eq!(dt.round(4).nanosecond(), 084_700_000);
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assert_eq!(dt.round(3).nanosecond(), 085_000_000);
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assert_eq!(dt.round(2).nanosecond(), 080_000_000);
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assert_eq!(dt.round(1).nanosecond(), 100_000_000);
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assert_eq!(dt.round(0).nanosecond(), 0);
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assert_eq!(dt.round(0).second(), 13);
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let dt = Utc.ymd(2018, 1, 11).and_hms_nano(10, 5, 27, 750_500_000);
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assert_eq!(dt.round(9), dt);
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assert_eq!(dt.round(4), dt);
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assert_eq!(dt.round(3).nanosecond(), 751_000_000);
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assert_eq!(dt.round(2).nanosecond(), 750_000_000);
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assert_eq!(dt.round(1).nanosecond(), 800_000_000);
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assert_eq!(dt.round(0).nanosecond(), 0);
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assert_eq!(dt.round(0).second(), 28);
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}
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#[test]
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fn test_round_leap_nanos() {
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let dt = Utc.ymd(2016, 12, 31).and_hms_nano(23, 59, 59, 1_750_500_000);
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assert_eq!(dt.round(9), dt);
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assert_eq!(dt.round(4), dt);
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assert_eq!(dt.round(2).nanosecond(), 1_750_000_000);
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assert_eq!(dt.round(1).nanosecond(), 1_800_000_000);
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assert_eq!(dt.round(1).second(), 59);
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assert_eq!(dt.round(0).nanosecond(), 0);
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assert_eq!(dt.round(0).second(), 0);
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}
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#[test]
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fn test_trunc() {
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let pst = FixedOffset::east(8 * 60 * 60);
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let dt = pst.ymd(2018, 1, 11).and_hms_nano(10, 5, 13, 084_660_684);
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assert_eq!(dt.trunc(10), dt);
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assert_eq!(dt.trunc(9), dt);
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assert_eq!(dt.trunc(8).nanosecond(), 084_660_680);
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assert_eq!(dt.trunc(7).nanosecond(), 084_660_600);
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assert_eq!(dt.trunc(6).nanosecond(), 084_660_000);
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assert_eq!(dt.trunc(5).nanosecond(), 084_660_000);
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assert_eq!(dt.trunc(4).nanosecond(), 084_600_000);
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assert_eq!(dt.trunc(3).nanosecond(), 084_000_000);
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assert_eq!(dt.trunc(2).nanosecond(), 080_000_000);
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assert_eq!(dt.trunc(1).nanosecond(), 0);
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assert_eq!(dt.trunc(0).nanosecond(), 0);
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assert_eq!(dt.trunc(0).second(), 13);
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let dt = pst.ymd(2018, 1, 11).and_hms_nano(10, 5, 27, 750_500_000);
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assert_eq!(dt.trunc(9), dt);
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assert_eq!(dt.trunc(4), dt);
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assert_eq!(dt.trunc(3).nanosecond(), 750_000_000);
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assert_eq!(dt.trunc(2).nanosecond(), 750_000_000);
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assert_eq!(dt.trunc(1).nanosecond(), 700_000_000);
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assert_eq!(dt.trunc(0).nanosecond(), 0);
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assert_eq!(dt.trunc(0).second(), 27);
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}
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#[test]
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fn test_trunc_leap_nanos() {
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let dt = Utc.ymd(2016, 12, 31).and_hms_nano(23, 59, 59, 1_750_500_000);
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assert_eq!(dt.trunc(9), dt);
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assert_eq!(dt.trunc(4), dt);
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assert_eq!(dt.trunc(2).nanosecond(), 1_750_000_000);
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assert_eq!(dt.trunc(1).nanosecond(), 1_700_000_000);
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assert_eq!(dt.trunc(1).second(), 59);
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assert_eq!(dt.trunc(0).nanosecond(), 1_000_000_000);
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assert_eq!(dt.trunc(0).second(), 59);
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}
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}
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