diff --git a/library/core/src/time.rs b/library/core/src/time.rs index 243c044b5d9d0..d653f715f6d47 100644 --- a/library/core/src/time.rs +++ b/library/core/src/time.rs @@ -730,9 +730,9 @@ impl Duration { /// // subnormal float /// let res = Duration::from_secs_f64(f64::from_bits(1)); /// assert_eq!(res, Duration::new(0, 0)); - /// // conversion uses truncation, not rounding + /// // conversion uses rounding /// let res = Duration::from_secs_f64(0.999e-9); - /// assert_eq!(res, Duration::new(0, 0)); + /// assert_eq!(res, Duration::new(0, 1)); /// ``` #[stable(feature = "duration_float", since = "1.38.0")] #[must_use] @@ -760,17 +760,17 @@ impl Duration { /// let res = Duration::from_secs_f32(1e-20); /// assert_eq!(res, Duration::new(0, 0)); /// let res = Duration::from_secs_f32(4.2e-7); - /// assert_eq!(res, Duration::new(0, 419)); + /// assert_eq!(res, Duration::new(0, 420)); /// let res = Duration::from_secs_f32(2.7); - /// assert_eq!(res, Duration::new(2, 700_000_047)); + /// assert_eq!(res, Duration::new(2, 700_000_048)); /// let res = Duration::from_secs_f32(3e10); /// assert_eq!(res, Duration::new(30_000_001_024, 0)); /// // subnormal float /// let res = Duration::from_secs_f32(f32::from_bits(1)); /// assert_eq!(res, Duration::new(0, 0)); - /// // conversion uses truncation, not rounding + /// // conversion uses rounding /// let res = Duration::from_secs_f32(0.999e-9); - /// assert_eq!(res, Duration::new(0, 0)); + /// assert_eq!(res, Duration::new(0, 1)); /// ``` #[stable(feature = "duration_float", since = "1.38.0")] #[must_use] @@ -815,7 +815,7 @@ impl Duration { /// use std::time::Duration; /// /// let dur = Duration::new(2, 700_000_000); - /// assert_eq!(dur.mul_f32(3.14), Duration::new(8, 478_000_640)); + /// assert_eq!(dur.mul_f32(3.14), Duration::new(8, 478_000_641)); /// assert_eq!(dur.mul_f32(3.14e5), Duration::new(847800, 0)); /// ``` #[stable(feature = "duration_float", since = "1.38.0")] @@ -838,8 +838,7 @@ impl Duration { /// /// let dur = Duration::new(2, 700_000_000); /// assert_eq!(dur.div_f64(3.14), Duration::new(0, 859_872_611)); - /// // note that truncation is used, not rounding - /// assert_eq!(dur.div_f64(3.14e5), Duration::new(0, 8_598)); + /// assert_eq!(dur.div_f64(3.14e5), Duration::new(0, 8_599)); /// ``` #[stable(feature = "duration_float", since = "1.38.0")] #[must_use = "this returns the result of the operation, \ @@ -862,9 +861,8 @@ impl Duration { /// let dur = Duration::new(2, 700_000_000); /// // note that due to rounding errors result is slightly /// // different from 0.859_872_611 - /// assert_eq!(dur.div_f32(3.14), Duration::new(0, 859_872_579)); - /// // note that truncation is used, not rounding - /// assert_eq!(dur.div_f32(3.14e5), Duration::new(0, 8_598)); + /// assert_eq!(dur.div_f32(3.14), Duration::new(0, 859_872_580)); + /// assert_eq!(dur.div_f32(3.14e5), Duration::new(0, 8_599)); /// ``` #[stable(feature = "duration_float", since = "1.38.0")] #[must_use = "this returns the result of the operation, \ @@ -1272,19 +1270,53 @@ macro_rules! try_from_secs { let mant = (bits & MANT_MASK) | (MANT_MASK + 1); let exp = ((bits >> $mant_bits) & EXP_MASK) as i16 + MIN_EXP; - let (secs, nanos) = if exp < -30 { - // the input represents less than 1ns. + let (secs, nanos) = if exp < -31 { + // the input represents less than 1ns and can not be rounded to it (0u64, 0u32) } else if exp < 0 { // the input is less than 1 second let t = <$double_ty>::from(mant) << ($offset + exp); - let nanos = (u128::from(NANOS_PER_SEC) * u128::from(t)) >> ($mant_bits + $offset); - (0, nanos as u32) + let nanos_offset = $mant_bits + $offset; + let nanos_tmp = u128::from(NANOS_PER_SEC) * u128::from(t); + let nanos = (nanos_tmp >> nanos_offset) as u32; + + let rem_mask = (1 << nanos_offset) - 1; + let rem_msb_mask = 1 << (nanos_offset - 1); + let rem = nanos_tmp & rem_mask; + let is_tie = rem == rem_msb_mask; + let is_even = (nanos & 1) == 0; + let rem_msb = nanos_tmp & rem_msb_mask == 0; + let add_ns = !(rem_msb || (is_even && is_tie)); + + // f32 does not have enough presicion to trigger the second branch + // since it can not represent numbers between 0.999_999_940_395 and 1.0. + let nanos = nanos + add_ns as u32; + if ($mant_bits == 23) || (nanos != NANOS_PER_SEC) { (0, nanos) } else { (1, 0) } } else if exp < $mant_bits { - let secs = mant >> ($mant_bits - exp); + let secs = u64::from(mant >> ($mant_bits - exp)); let t = <$double_ty>::from((mant << exp) & MANT_MASK); - let nanos = (<$double_ty>::from(NANOS_PER_SEC) * t) >> $mant_bits; - (u64::from(secs), nanos as u32) + let nanos_offset = $mant_bits; + let nanos_tmp = <$double_ty>::from(NANOS_PER_SEC) * t; + let nanos = (nanos_tmp >> nanos_offset) as u32; + + let rem_mask = (1 << nanos_offset) - 1; + let rem_msb_mask = 1 << (nanos_offset - 1); + let rem = nanos_tmp & rem_mask; + let is_tie = rem == rem_msb_mask; + let is_even = (nanos & 1) == 0; + let rem_msb = nanos_tmp & rem_msb_mask == 0; + let add_ns = !(rem_msb || (is_even && is_tie)); + + // f32 does not have enough presicion to trigger the second branch. + // For example, it can not represent numbers between 1.999_999_880... + // and 2.0. Bigger values result in even smaller presicion of the + // fractional part. + let nanos = nanos + add_ns as u32; + if ($mant_bits == 23) || (nanos != NANOS_PER_SEC) { + (secs, nanos) + } else { + (secs + 1, 0) + } } else if exp < 64 { // the input has no fractional part let secs = u64::from(mant) << (exp - $mant_bits); @@ -1315,17 +1347,14 @@ impl Duration { /// let res = Duration::try_from_secs_f32(1e-20); /// assert_eq!(res, Ok(Duration::new(0, 0))); /// let res = Duration::try_from_secs_f32(4.2e-7); - /// assert_eq!(res, Ok(Duration::new(0, 419))); + /// assert_eq!(res, Ok(Duration::new(0, 420))); /// let res = Duration::try_from_secs_f32(2.7); - /// assert_eq!(res, Ok(Duration::new(2, 700_000_047))); + /// assert_eq!(res, Ok(Duration::new(2, 700_000_048))); /// let res = Duration::try_from_secs_f32(3e10); /// assert_eq!(res, Ok(Duration::new(30_000_001_024, 0))); /// // subnormal float: /// let res = Duration::try_from_secs_f32(f32::from_bits(1)); /// assert_eq!(res, Ok(Duration::new(0, 0))); - /// // conversion uses truncation, not rounding - /// let res = Duration::try_from_secs_f32(0.999e-9); - /// assert_eq!(res, Ok(Duration::new(0, 0))); /// /// let res = Duration::try_from_secs_f32(-5.0); /// assert!(res.is_err()); @@ -1333,6 +1362,30 @@ impl Duration { /// assert!(res.is_err()); /// let res = Duration::try_from_secs_f32(2e19); /// assert!(res.is_err()); + /// + /// // the conversion uses rounding with tie resolution to even + /// let res = Duration::try_from_secs_f32(0.999e-9); + /// assert_eq!(res, Ok(Duration::new(0, 1))); + /// + /// // this float represents exactly 976562.5e-9 + /// let val = f32::from_bits(0x3A80_0000); + /// let res = Duration::try_from_secs_f32(val); + /// assert_eq!(res, Ok(Duration::new(0, 976_562))); + /// + /// // this float represents exactly 2929687.5e-9 + /// let val = f32::from_bits(0x3B40_0000); + /// let res = Duration::try_from_secs_f32(val); + /// assert_eq!(res, Ok(Duration::new(0, 2_929_688))); + /// + /// // this float represents exactly 1.000_976_562_5 + /// let val = f32::from_bits(0x3F802000); + /// let res = Duration::try_from_secs_f32(val); + /// assert_eq!(res, Ok(Duration::new(1, 976_562))); + /// + /// // this float represents exactly 1.002_929_687_5 + /// let val = f32::from_bits(0x3F806000); + /// let res = Duration::try_from_secs_f32(val); + /// assert_eq!(res, Ok(Duration::new(1, 2_929_688))); /// ``` #[unstable(feature = "duration_checked_float", issue = "83400")] #[inline] @@ -1372,9 +1425,6 @@ impl Duration { /// // subnormal float /// let res = Duration::try_from_secs_f64(f64::from_bits(1)); /// assert_eq!(res, Ok(Duration::new(0, 0))); - /// // conversion uses truncation, not rounding - /// let res = Duration::try_from_secs_f32(0.999e-9); - /// assert_eq!(res, Ok(Duration::new(0, 0))); /// /// let res = Duration::try_from_secs_f64(-5.0); /// assert!(res.is_err()); @@ -1382,6 +1432,38 @@ impl Duration { /// assert!(res.is_err()); /// let res = Duration::try_from_secs_f64(2e19); /// assert!(res.is_err()); + /// + /// // the conversion uses rounding with tie resolution to even + /// let res = Duration::try_from_secs_f64(0.999e-9); + /// assert_eq!(res, Ok(Duration::new(0, 1))); + /// let res = Duration::try_from_secs_f64(0.999_999_999_499); + /// assert_eq!(res, Ok(Duration::new(0, 999_999_999))); + /// let res = Duration::try_from_secs_f64(0.999_999_999_501); + /// assert_eq!(res, Ok(Duration::new(1, 0))); + /// let res = Duration::try_from_secs_f64(42.999_999_999_499); + /// assert_eq!(res, Ok(Duration::new(42, 999_999_999))); + /// let res = Duration::try_from_secs_f64(42.999_999_999_501); + /// assert_eq!(res, Ok(Duration::new(43, 0))); + /// + /// // this float represents exactly 976562.5e-9 + /// let val = f64::from_bits(0x3F50_0000_0000_0000); + /// let res = Duration::try_from_secs_f64(val); + /// assert_eq!(res, Ok(Duration::new(0, 976_562))); + /// + /// // this float represents exactly 2929687.5e-9 + /// let val = f64::from_bits(0x3F68_0000_0000_0000); + /// let res = Duration::try_from_secs_f64(val); + /// assert_eq!(res, Ok(Duration::new(0, 2_929_688))); + /// + /// // this float represents exactly 1.000_976_562_5 + /// let val = f64::from_bits(0x3FF0_0400_0000_0000); + /// let res = Duration::try_from_secs_f64(val); + /// assert_eq!(res, Ok(Duration::new(1, 976_562))); + /// + /// // this float represents exactly 1.002_929_687_5 + /// let val = f64::from_bits(0x3_FF00_C000_0000_000); + /// let res = Duration::try_from_secs_f64(val); + /// assert_eq!(res, Ok(Duration::new(1, 2_929_688))); /// ``` #[unstable(feature = "duration_checked_float", issue = "83400")] #[inline]