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core: Add and use vec::reserve_at_least

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This reserves in powers of two
This commit is contained in:
Brian Anderson
2012-03-28 22:49:28 -07:00
parent 8e743b2981
commit b3d7823381
1 changed files with 22 additions and 3 deletions
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25
src/libcore/vec.rs
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@@ -1,7 +1,6 @@
#[doc = "Vectors"];
import option::{some, none};
import uint::next_power_of_two;
import ptr::addr_of;
export init_op;
@@ -9,6 +8,7 @@ export is_empty;
export is_not_empty;
export same_length;
export reserve;
export reserve_at_least;
export len;
export from_fn;
export from_elem;
@@ -115,6 +115,25 @@ fn reserve<T>(&v: [const T], n: uint) {
rustrt::vec_reserve_shared(sys::get_type_desc::<T>(), v, n);
}
#[doc = "
Reserves capacity for at least `n` elements in the given vector.
This function will over-allocate in order to amortize the allocation costs
in scenarios where the caller may need to repeatedly reserve additional
space.
If the capacity for `v` is already equal to or greater than the requested
capacity, then no action is taken.
# Arguments
* v - A vector
* n - The number of elements to reserve space for
"]
fn reserve_at_least<T>(&v: [const T], n: uint) {
reserve(v, uint::next_power_of_two(n));
}
#[doc = "Returns the length of a vector"]
#[inline(always)]
pure fn len<T>(&&v: [const T]) -> uint unsafe {
@@ -364,7 +383,7 @@ Expands a vector in place, initializing the new elements to a given value
* initval - The value for the new elements
"]
fn grow<T: copy>(&v: [const T], n: uint, initval: T) {
reserve(v, next_power_of_two(len(v) + n));
reserve_at_least(v, len(v) + n);
let mut i: uint = 0u;
while i < n { v += [initval]; i += 1u; }
}
@@ -383,7 +402,7 @@ Function `init_op` is called `n` times with the values [0..`n`)
value
"]
fn grow_fn<T>(&v: [const T], n: uint, op: init_op<T>) {
reserve(v, next_power_of_two(len(v) + n));
reserve_at_least(v, len(v) + n);
let mut i: uint = 0u;
while i < n { v += [op(i)]; i += 1u; }
}