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Stepan KoltsovandCarl Lerche
7110d57b2f
Round up to power of 2 is not necessary, because `reserve` already
doubles previous capacity in
```
new_cap = cmp::max(
cmp::max(v.capacity() << 1, new_cap),
original_capacity);
```
which makes `reserve` calls constant in average. Avoiding rounding
up prevents `reserve` from wasting space when caller knows exactly
what space they need.
Patch adds three tests which would fail before this test. The most
important is this:
```
#[test]
fn reserve_in_arc_unique_does_not_overallocate() {
let mut bytes = BytesMut::with_capacity(1000);
bytes.take();
// now bytes is Arc and refcount == 1
assert_eq!(1000, bytes.capacity());
bytes.reserve(2001);
assert_eq!(2001, bytes.capacity());
}
```
It asserts that when user requests more than double of current
capacity, exactly the requested amount of memory is allocated and
is not wasted to next power of two.