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Add helper functions for next_power_of_two and checked_next_power_of_two

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This commit is contained in:
Irfan Hudda 2017-04-28 21:50:02 +05:30
parent f7bd370818
commit 8f9caff988
1 changed files with 14 additions and 10 deletions
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24
src/libcore/num/mod.rs
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@ -2327,6 +2327,18 @@ macro_rules! uint_impl {
(self.wrapping_sub(1)) & self == 0 && !(self == 0)
}
fn round_up_to_one_less_than_a_power_of_two(self) -> Self {
let bits = size_of::<Self>() as u32 * 8;
let z = self.leading_zeros();
(if z == bits { 0 as Self } else { !0 }).wrapping_shr(z)
}
fn one_less_than_next_power_of_two(self) -> Self {
self.wrapping_sub(1)
.round_up_to_one_less_than_a_power_of_two()
.wrapping_add(if self == 0 { 1 } else { 0 })
}
/// Returns the smallest power of two greater than or equal to `self`.
/// More details about overflow behavior can be found in [RFC 560].
///
@ -2343,13 +2355,7 @@ macro_rules! uint_impl {
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn next_power_of_two(self) -> Self {
let bits = size_of::<Self>() * 8;
let one: Self = 1;
if self == 0 {
1
} else {
one << (bits - (self - one).leading_zeros() as usize)
}
self.one_less_than_next_power_of_two() + 1
}
/// Returns the smallest power of two greater than or equal to `n`. If
@ -2367,9 +2373,7 @@ macro_rules! uint_impl {
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn checked_next_power_of_two(self) -> Option<Self> {
let bits = size_of::<Self>() * 8;
let one: Self = 1;
let npot = one << ((bits - self.wrapping_sub(one).leading_zeros() as usize) % bits);
let npot = self.one_less_than_next_power_of_two().wrapping_add(1);
if npot >= self {
Some(npot)
} else {