diff --git a/time/src/duration.rs b/time/src/duration.rs index 988cfa9eb..515f04a7b 100644 --- a/time/src/duration.rs +++ b/time/src/duration.rs @@ -51,6 +51,123 @@ impl fmt::Debug for Duration { } } +/// This is adapted from the `std` implementation, which uses mostly bit +/// operations to ensure the highest precision: +/// https://github.com/rust-lang/rust/blob/3a37c2f0523c87147b64f1b8099fc9df22e8c53e/library/core/src/time.rs#L1262-L1340 +/// Changes from `std` are marked and explained below. +macro_rules! try_from_secs { + ( + secs = $secs: expr, + mantissa_bits = $mant_bits: literal, + exponent_bits = $exp_bits: literal, + offset = $offset: literal, + bits_ty = $bits_ty:ty, + bits_ty_signed = $bits_ty_signed:ty, + double_ty = $double_ty:ty, + float_ty = $float_ty:ty, + is_nan = $is_nan:expr, + is_overflow = $is_overflow:expr, + ) => {{ + 'value: { + const MIN_EXP: i16 = 1 - (1i16 << $exp_bits) / 2; + const MANT_MASK: $bits_ty = (1 << $mant_bits) - 1; + const EXP_MASK: $bits_ty = (1 << $exp_bits) - 1; + + // Change from std: No error check for negative values necessary. + + let bits = $secs.to_bits(); + let mant = (bits & MANT_MASK) | (MANT_MASK + 1); + let exp = ((bits >> $mant_bits) & EXP_MASK) as i16 + MIN_EXP; + + let (secs, nanos) = if exp < -31 { + // the input represents less than 1ns and can not be rounded to it + (0u64, 0u32) + } else if exp < 0 { + // the input is less than 1 second + let t = <$double_ty>::from(mant) << ($offset + exp); + let nanos_offset = $mant_bits + $offset; + let nanos_tmp = u128::from(Nanosecond.per(Second)) * u128::from(t); + let nanos = (nanos_tmp >> nanos_offset) as u32; + + let rem_mask = (1 << nanos_offset) - 1; + let rem_msb_mask = 1 << (nanos_offset - 1); + let rem = nanos_tmp & rem_mask; + let is_tie = rem == rem_msb_mask; + let is_even = (nanos & 1) == 0; + let rem_msb = nanos_tmp & rem_msb_mask == 0; + let add_ns = !(rem_msb || (is_even && is_tie)); + + // f32 does not have enough precision to trigger the second branch + // since it can not represent numbers between 0.999_999_940_395 and 1.0. + let nanos = nanos + add_ns as u32; + if ($mant_bits == 23) || (nanos != Nanosecond.per(Second)) { + (0, nanos) + } else { + (1, 0) + } + } 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(Nanosecond.per(Second)) * 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 precision 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 precision of the + // fractional part. + let nanos = nanos + add_ns as u32; + if ($mant_bits == 23) || (nanos != Nanosecond.per(Second)) { + (secs, nanos) + } else { + (secs + 1, 0) + } + } else if exp < 63 { + // Change from std: The exponent here is 63 instead of 64, + // because i64::MAX + 1 is 2^63. + + // the input has no fractional part + let secs = u64::from(mant) << (exp - $mant_bits); + (secs, 0) + } else if bits == (i64::MIN as $float_ty).to_bits() { + // Change from std: Signed integers are asymmetrical in that + // iN::MIN is -iN::MAX - 1. So for example i8 covers the + // following numbers -128..=127. The check above (exp < 63) + // doesn't cover i64::MIN as that is -2^63, so we have this + // additional case to handle the asymmetry of iN::MIN. + break 'value Self::new_unchecked(i64::MIN, 0); + } else if $secs.is_nan() { + // Change from std: std doesn't differentiate between the error + // cases. + $is_nan + } else { + $is_overflow + }; + + // Change from std: All the code is mostly unmodified in that it + // simply calculates an unsigned integer. Here we extract the sign + // bit and assign it to the number. We basically manually do two's + // complement here, we could also use an if and just negate the + // numbers based on the sign, but it turns out to be quite a bit + // slower. + let mask = (bits as $bits_ty_signed) >> ($mant_bits + $exp_bits); + #[allow(trivial_numeric_casts)] + let secs_signed = ((secs as i64) ^ (mask as i64)) - (mask as i64); + #[allow(trivial_numeric_casts)] + let nanos_signed = ((nanos as i32) ^ (mask as i32)) - (mask as i32); + Self::new_unchecked(secs_signed, nanos_signed) + } + }}; +} + impl Duration { // region: constants /// Equivalent to `0.seconds()`. @@ -321,17 +438,18 @@ impl Duration { /// assert_eq!(Duration::seconds_f64(-0.5), -0.5.seconds()); /// ``` pub fn seconds_f64(seconds: f64) -> Self { - if seconds > i64::MAX as f64 || seconds < i64::MIN as f64 { - crate::expect_failed("overflow constructing `time::Duration`"); - } - if seconds.is_nan() { - crate::expect_failed("passed NaN to `time::Duration::seconds_f64`"); - } - let seconds_truncated = seconds as i64; - // This only works because we handle the overflow condition above. - let nanoseconds = - ((seconds - seconds_truncated as f64) * Nanosecond.per(Second) as f64) as i32; - Self::new_unchecked(seconds_truncated, nanoseconds) + try_from_secs!( + secs = seconds, + mantissa_bits = 52, + exponent_bits = 11, + offset = 44, + bits_ty = u64, + bits_ty_signed = i64, + double_ty = u128, + float_ty = f64, + is_nan = crate::expect_failed("passed NaN to `time::Duration::seconds_f64`"), + is_overflow = crate::expect_failed("overflow constructing `time::Duration`"), + ) } /// Creates a new `Duration` from the specified number of seconds represented as `f32`. @@ -342,17 +460,136 @@ impl Duration { /// assert_eq!(Duration::seconds_f32(-0.5), (-0.5).seconds()); /// ``` pub fn seconds_f32(seconds: f32) -> Self { - if seconds > i64::MAX as f32 || seconds < i64::MIN as f32 { - crate::expect_failed("overflow constructing `time::Duration`"); - } - if seconds.is_nan() { - crate::expect_failed("passed NaN to `time::Duration::seconds_f32`"); - } - let seconds_truncated = seconds as i64; - // This only works because we handle the overflow condition above. - let nanoseconds = - ((seconds - seconds_truncated as f32) * Nanosecond.per(Second) as f32) as i32; - Self::new_unchecked(seconds_truncated, nanoseconds) + try_from_secs!( + secs = seconds, + mantissa_bits = 23, + exponent_bits = 8, + offset = 41, + bits_ty = u32, + bits_ty_signed = i32, + double_ty = u64, + float_ty = f32, + is_nan = crate::expect_failed("passed NaN to `time::Duration::seconds_f32`"), + is_overflow = crate::expect_failed("overflow constructing `time::Duration`"), + ) + } + + /// Creates a new `Duration` from the specified number of seconds + /// represented as `f64`. Any values that are out of bounds are saturated at + /// the minimum or maximum respectively. `NaN` gets turned into a `Duration` + /// of 0 seconds. + /// + /// ```rust + /// # use time::{Duration, ext::NumericalDuration}; + /// assert_eq!(Duration::saturating_seconds_f64(0.5), 0.5.seconds()); + /// assert_eq!(Duration::saturating_seconds_f64(-0.5), -0.5.seconds()); + /// assert_eq!(Duration::saturating_seconds_f64(f64::NAN), Duration::new(0, 0)); + /// assert_eq!(Duration::saturating_seconds_f64(f64::NEG_INFINITY), Duration::MIN); + /// assert_eq!(Duration::saturating_seconds_f64(f64::INFINITY), Duration::MAX); + /// ``` + pub fn saturating_seconds_f64(seconds: f64) -> Self { + try_from_secs!( + secs = seconds, + mantissa_bits = 52, + exponent_bits = 11, + offset = 44, + bits_ty = u64, + bits_ty_signed = i64, + double_ty = u128, + float_ty = f64, + is_nan = (0, 0), + is_overflow = return if seconds < 0.0 { + Self::new_unchecked(i64::MIN, -999_999_999) + } else { + Self::new_unchecked(i64::MAX, 999_999_999) + }, + ) + } + + /// Creates a new `Duration` from the specified number of seconds + /// represented as `f32`. Any values that are out of bounds are saturated at + /// the minimum or maximum respectively. `NaN` gets turned into a `Duration` + /// of 0 seconds. + /// + /// ```rust + /// # use time::{Duration, ext::NumericalDuration}; + /// assert_eq!(Duration::saturating_seconds_f32(0.5), 0.5.seconds()); + /// assert_eq!(Duration::saturating_seconds_f32(-0.5), (-0.5).seconds()); + /// assert_eq!(Duration::saturating_seconds_f32(f32::NAN), Duration::new(0, 0)); + /// assert_eq!(Duration::saturating_seconds_f32(f32::NEG_INFINITY), Duration::MIN); + /// assert_eq!(Duration::saturating_seconds_f32(f32::INFINITY), Duration::MAX); + /// ``` + pub fn saturating_seconds_f32(seconds: f32) -> Self { + try_from_secs!( + secs = seconds, + mantissa_bits = 23, + exponent_bits = 8, + offset = 41, + bits_ty = u32, + bits_ty_signed = i32, + double_ty = u64, + float_ty = f32, + is_nan = (0, 0), + is_overflow = return if seconds < 0.0 { + Self::new_unchecked(i64::MIN, -999_999_999) + } else { + Self::new_unchecked(i64::MAX, 999_999_999) + }, + ) + } + + /// Creates a new `Duration` from the specified number of seconds + /// represented as `f64`. Returns `None` if the `Duration` can't be + /// represented. + /// + /// ```rust + /// # use time::{Duration, ext::NumericalDuration}; + /// assert_eq!(Duration::checked_seconds_f64(0.5), Some(0.5.seconds())); + /// assert_eq!(Duration::checked_seconds_f64(-0.5), Some(-0.5.seconds())); + /// assert_eq!(Duration::checked_seconds_f64(f64::NAN), None); + /// assert_eq!(Duration::checked_seconds_f64(f64::NEG_INFINITY), None); + /// assert_eq!(Duration::checked_seconds_f64(f64::INFINITY), None); + /// ``` + pub fn checked_seconds_f64(seconds: f64) -> Option { + Some(try_from_secs!( + secs = seconds, + mantissa_bits = 52, + exponent_bits = 11, + offset = 44, + bits_ty = u64, + bits_ty_signed = i64, + double_ty = u128, + float_ty = f64, + is_nan = return None, + is_overflow = return None, + )) + } + + /// Creates a new `Duration` from the specified number of seconds + /// represented as `f32`. Returns `None` if the `Duration` can't be + /// represented. + /// + /// ```rust + /// # use time::{Duration, ext::NumericalDuration}; + /// assert_eq!(Duration::checked_seconds_f32(0.5), Some(0.5.seconds())); + /// assert_eq!(Duration::checked_seconds_f32(-0.5), Some(-0.5.seconds())); + /// assert_eq!(Duration::checked_seconds_f32(f32::NAN), None); + /// assert_eq!(Duration::checked_seconds_f32(f32::NEG_INFINITY), None); + /// assert_eq!(Duration::checked_seconds_f32(f32::INFINITY), None); + /// ``` + pub fn checked_seconds_f32(seconds: f32) -> Option { + Some(try_from_secs!( + secs = seconds, + mantissa_bits = 23, + exponent_bits = 8, + offset = 41, + bits_ty = u32, + bits_ty_signed = i32, + double_ty = u64, + float_ty = f32, + is_nan = return None, + is_overflow = return None, + )) } /// Create a new `Duration` with the given number of milliseconds.