/// Prepend an element to the deque
pub fn add_front(&mut self, t: T) {
if self.nelts == self.elts.len() {
- grow(self.nelts, self.lo, &mut self.elts);
+ grow(self.nelts, &mut self.lo, &mut self.elts);
}
if self.lo == 0u {
self.lo = self.elts.len() - 1u;
/// Append an element to the deque
pub fn add_back(&mut self, t: T) {
if self.nelts == self.elts.len() {
- grow(self.nelts, self.lo, &mut self.elts);
+ grow(self.nelts, &mut self.lo, &mut self.elts);
}
let hi = self.raw_index(self.nelts);
self.elts[hi] = Some(t);
/// Grow is only called on full elts, so nelts is also len(elts), unlike
/// elsewhere.
-fn grow<T>(nelts: uint, lo: uint, elts: &mut ~[Option<T>]) {
+fn grow<T>(nelts: uint, loptr: &mut uint, elts: &mut ~[Option<T>]) {
assert_eq!(nelts, elts.len());
- let newlen = elts.capacity() * 2;
+ let lo = *loptr;
+ let newlen = nelts * 2;
elts.reserve(newlen);
/* fill with None */
for uint::range(elts.len(), elts.capacity()) |_| {
elts.push(None);
}
- /* move the former wraparound to the new half */
- for uint::range(0, lo) |i| {
- elts.swap(i, nelts + i);
+
+ /*
+ Move the shortest half into the newly reserved area.
+ lo ---->|
+ nelts ----------->|
+ [o o o|o o o o o]
+ A [. . .|o o o o o o o o|. . . . .]
+ B [o o o|. . . . . . . .|o o o o o]
+ */
+
+ assert!(newlen - nelts/2 >= nelts);
+ if lo <= (nelts - lo) { // A
+ for uint::range(0, lo) |i| {
+ elts.swap(i, nelts + i);
+ }
+ } else { // B
+ for uint::range(lo, nelts) |i| {
+ elts.swap(i, newlen - nelts + i);
+ }
+ *loptr += newlen - nelts;
}
}