bjoernager/rust
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Reform power_of_two methods for perf increase & semantic change to consider 0 not a power of 2.

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Vec panics when attempting to reserve capacity > int::MAX (uint::MAX / 2).
This commit is contained in:
Aaron Liblong 2014-12-08 01:03:35 -05:00
parent 99d6956c3b
commit f6328b60da
4 changed files with 43 additions and 37 deletions
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31
src/libstd/num/mod.rs
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@ -664,11 +664,32 @@ mod tests {
assert_eq!(third.checked_mul(4), None);
}
macro_rules! test_is_power_of_two {
($test_name:ident, $T:ident) => (
fn $test_name() {
#![test]
assert_eq!((0 as $T).is_power_of_two(), false);
assert_eq!((1 as $T).is_power_of_two(), true);
assert_eq!((2 as $T).is_power_of_two(), true);
assert_eq!((3 as $T).is_power_of_two(), false);
assert_eq!((4 as $T).is_power_of_two(), true);
assert_eq!((5 as $T).is_power_of_two(), false);
assert!(($T::MAX / 2 + 1).is_power_of_two(), true);
}
)
}
test_is_power_of_two!{ test_is_power_of_two_u8, u8 }
test_is_power_of_two!{ test_is_power_of_two_u16, u16 }
test_is_power_of_two!{ test_is_power_of_two_u32, u32 }
test_is_power_of_two!{ test_is_power_of_two_u64, u64 }
test_is_power_of_two!{ test_is_power_of_two_uint, uint }
macro_rules! test_next_power_of_two {
($test_name:ident, $T:ident) => (
fn $test_name() {
#![test]
assert_eq!((0 as $T).next_power_of_two(), 0);
assert_eq!((0 as $T).next_power_of_two(), 1);
let mut next_power = 1;
for i in range::<$T>(1, 40) {
assert_eq!(i.next_power_of_two(), next_power);
@ -688,15 +709,15 @@ mod tests {
($test_name:ident, $T:ident) => (
fn $test_name() {
#![test]
assert_eq!((0 as $T).checked_next_power_of_two(), None);
assert_eq!((0 as $T).checked_next_power_of_two(), Some(1));
assert!(($T::MAX / 2).checked_next_power_of_two().is_some());
assert_eq!(($T::MAX - 1).checked_next_power_of_two(), None);
assert_eq!($T::MAX.checked_next_power_of_two(), None);
let mut next_power = 1;
for i in range::<$T>(1, 40) {
assert_eq!(i.checked_next_power_of_two(), Some(next_power));
if i == next_power { next_power *= 2 }
}
assert!(($T::MAX / 2).checked_next_power_of_two().is_some());
assert_eq!(($T::MAX - 1).checked_next_power_of_two(), None);
assert_eq!($T::MAX.checked_next_power_of_two(), None);
}
)
}