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implement tie to even

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Артём Павлов [Artyom Pavlov] 2022-05-25 05:01:11 +03:00
parent 65c75b2db7
commit c2d8445cde
1 changed files with 73 additions and 19 deletions
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92
library/core/src/time.rs
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@ -1270,8 +1270,8 @@ 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
@ -1279,27 +1279,37 @@ macro_rules! try_from_secs {
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;
if nanos_tmp & (1 << (nanos_offset - 1)) == 0 {
(0, nanos)
} else if nanos + 1 != NANOS_PER_SEC {
(0, nanos + 1)
} else {
(1, 0)
}
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));
// note that neither `f32`, nor `f64` can represent
// 0.999_999_999_5 exactly, so the nanos part
// never will be equal to 10^9.
(0, nanos + add_ns as u32)
} else if exp < $mant_bits {
let secs = u64::from(mant >> ($mant_bits - exp));
let t = <$double_ty>::from((mant << exp) & MANT_MASK);
let nanos_offset = $mant_bits;
let nanos_tmp = <$double_ty>::from(NANOS_PER_SEC) * t;
let nanos = (nanos_tmp >> $mant_bits) as u32;
if nanos_tmp & (1 << ($mant_bits - 1)) == 0 {
(secs, nanos)
} else if nanos + 1 != NANOS_PER_SEC {
(secs, nanos + 1)
} else {
// `secs + 1` can not overflow since `exp` is less than `$mant_bits`
// and the latter is less than 64 bits for both `f32` and `f64`
(secs + 1, 0)
}
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));
// neither `f32`, nor `f64` can represent x.999_999_999_5 exactly,
// so the nanos part never will be equal to 10^9
(secs, nanos + add_ns as u32)
} else if exp < 64 {
// the input has no fractional part
let secs = u64::from(mant) << (exp - $mant_bits);
@ -1348,6 +1358,28 @@ impl Duration {
/// assert!(res.is_err());
/// let res = Duration::try_from_secs_f32(2e19);
/// assert!(res.is_err());
///
/// // this method uses round to nearest, ties to even
///
/// // 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]
@ -1397,6 +1429,28 @@ impl Duration {
/// assert!(res.is_err());
/// let res = Duration::try_from_secs_f64(2e19);
/// assert!(res.is_err());
///
/// // this method uses round to nearest, ties to even
///
/// // 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]