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Add checked operation methods to Duration
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Eugene Bulkin committed Sep 14, 2016
1 parent 1fca1ab commit 606cded
Showing 1 changed file with 162 additions and 0 deletions.
162 changes: 162 additions & 0 deletions src/libstd/time/duration.rs
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Expand Up @@ -97,6 +97,130 @@ impl Duration {
#[stable(feature = "duration", since = "1.3.0")]
#[inline]
pub fn subsec_nanos(&self) -> u32 { self.nanos }

/// Checked duration addition. Computes `self + other`, returning `None`
/// if overflow occurred.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// assert_eq!(Duration::new(0, 0).checked_add(Duration::new(0, 1)), Some(Duration::new(0, 1)));
/// assert_eq!(Duration::new(1, 0).checked_add(Duration::new(::u64::MAX, 0)), None);
/// ```
#[unstable(feature = "duration_checked_ops", issue = "35774")]
#[inline]
pub fn checked_add(self, rhs: Duration) -> Option<Duration> {
if let Some(mut secs) = self.secs.checked_add(rhs.secs) {
let mut nanos = self.nanos + rhs.nanos;
if nanos >= NANOS_PER_SEC {
nanos -= NANOS_PER_SEC;
if let Some(new_secs) = secs.checked_add(1) {
secs = new_secs;
} else {
return None;
}
}
debug_assert!(nanos < NANOS_PER_SEC);
Some(Duration {
secs: secs,
nanos: nanos,
})
} else {
None
}
}

/// Checked duration subtraction. Computes `self + other`, returning `None`
/// if the result would be negative or if underflow occurred.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// assert_eq!(Duration::new(0, 1).checked_sub(Duration::new(0, 0)), Some(Duration::new(0, 1)));
/// assert_eq!(Duration::new(0, 0).checked_sub(Duration::new(0, 1)), None);
/// ```
#[unstable(feature = "duration_checked_ops", issue = "35774")]
#[inline]
pub fn checked_sub(self, rhs: Duration) -> Option<Duration> {
if let Some(mut secs) = self.secs.checked_sub(rhs.secs) {
let nanos = if self.nanos >= rhs.nanos {
self.nanos - rhs.nanos
} else {
if let Some(sub_secs) = secs.checked_sub(1) {
secs = sub_secs;
self.nanos + NANOS_PER_SEC - rhs.nanos
} else {
return None;
}
};
debug_assert!(nanos < NANOS_PER_SEC);
Some(Duration { secs: secs, nanos: nanos })
} else {
None
}
}

/// Checked integer multiplication. Computes `self * other`, returning
/// `None` if underflow or overflow occurred.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// assert_eq!(Duration::new(0, 500_000_001).checked_mul(2), Some(Duration::new(1, 2)));
/// assert_eq!(Duration::new(::u64::MAX - 1, 0).checked_mul(2), None);
/// ```
#[unstable(feature = "duration_checked_ops", issue = "35774")]
#[inline]
pub fn checked_mul(self, rhs: u32) -> Option<Duration> {
// Multiply nanoseconds as u64, because it cannot overflow that way.
let total_nanos = self.nanos as u64 * rhs as u64;
let extra_secs = total_nanos / (NANOS_PER_SEC as u64);
let nanos = (total_nanos % (NANOS_PER_SEC as u64)) as u32;
if let Some(secs) = self.secs
.checked_mul(rhs as u64)
.and_then(|s| s.checked_add(extra_secs)) {
debug_assert!(nanos < NANOS_PER_SEC);
Some(Duration {
secs: secs,
nanos: nanos,
})
} else {
None
}
}

/// Checked duration division. Computes `self / other`, returning `None`
/// if `other == 0` or the operation results in underflow or overflow.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// assert_eq!(Duration::new(2, 0).checked_div(2), Some(Duration::new(1, 0)));
/// assert_eq!(Duration::new(1, 0).checked_div(2), Some(Duration::new(0, 500_000_000)));
/// assert_eq!(Duration::new(2, 0).checked_div(0), None);
/// ```
#[unstable(feature = "duration_checked_ops", issue = "35774")]
#[inline]
pub fn checked_div(self, rhs: u32) -> Option<Duration> {
if rhs != 0 {
let secs = self.secs / (rhs as u64);
let carry = self.secs - secs * (rhs as u64);
let extra_nanos = carry * (NANOS_PER_SEC as u64) / (rhs as u64);
let nanos = self.nanos / rhs + (extra_nanos as u32);
debug_assert!(nanos < NANOS_PER_SEC);
Some(Duration { secs: secs, nanos: nanos })
} else {
None
}
}
}

#[stable(feature = "duration", since = "1.3.0")]
Expand Down Expand Up @@ -234,6 +358,15 @@ mod tests {
Duration::new(1, 1));
}

#[test]
fn checked_add() {
assert_eq!(Duration::new(0, 0).checked_add(Duration::new(0, 1)),
Some(Duration::new(0, 1)));
assert_eq!(Duration::new(0, 500_000_000).checked_add(Duration::new(0, 500_000_001)),
Some(Duration::new(1, 1)));
assert_eq!(Duration::new(1, 0).checked_add(Duration::new(::u64::MAX, 0)), None);
}

#[test]
fn sub() {
assert_eq!(Duration::new(0, 1) - Duration::new(0, 0),
Expand All @@ -244,6 +377,18 @@ mod tests {
Duration::new(0, 999_999_999));
}

#[test]
fn checked_sub() {
let zero = Duration::new(0, 0);
let one_nano = Duration::new(0, 1);
let one_sec = Duration::new(1, 0);
assert_eq!(one_nano.checked_sub(zero), Some(Duration::new(0, 1)));
assert_eq!(one_sec.checked_sub(one_nano),
Some(Duration::new(0, 999_999_999)));
assert_eq!(zero.checked_sub(one_nano), None);
assert_eq!(zero.checked_sub(one_sec), None);
}

#[test] #[should_panic]
fn sub_bad1() {
Duration::new(0, 0) - Duration::new(0, 1);
Expand All @@ -263,11 +408,28 @@ mod tests {
Duration::new(2000, 4000));
}

#[test]
fn checked_mul() {
assert_eq!(Duration::new(0, 1).checked_mul(2), Some(Duration::new(0, 2)));
assert_eq!(Duration::new(1, 1).checked_mul(3), Some(Duration::new(3, 3)));
assert_eq!(Duration::new(0, 500_000_001).checked_mul(4), Some(Duration::new(2, 4)));
assert_eq!(Duration::new(0, 500_000_001).checked_mul(4000),
Some(Duration::new(2000, 4000)));
assert_eq!(Duration::new(::u64::MAX - 1, 0).checked_mul(2), None);
}

#[test]
fn div() {
assert_eq!(Duration::new(0, 1) / 2, Duration::new(0, 0));
assert_eq!(Duration::new(1, 1) / 3, Duration::new(0, 333_333_333));
assert_eq!(Duration::new(99, 999_999_000) / 100,
Duration::new(0, 999_999_990));
}

#[test]
fn checked_div() {
assert_eq!(Duration::new(2, 0).checked_div(2), Some(Duration::new(1, 0)));
assert_eq!(Duration::new(1, 0).checked_div(2), Some(Duration::new(0, 500_000_000)));
assert_eq!(Duration::new(2, 0).checked_div(0), None);
}
}

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