auto merge of #8186 : huonw/rust/hashmap-=rt, r=Aatch

The `new` constructor uses the task-local RNG to retrieve seeds for the
two key values, which requires the runtime. Exposing a constructor that
takes the keys directly allows HashMaps to be used in programs that wish
to avoid the runtime.

src/libstd/hashmap.rs

@@ -61,27 +61,7 @@ enum SearchResult {
 
 #[inline]
 fn resize_at(capacity: uint) -> uint {
- ((capacity as float) * 3. / 4.) as uint
-}
-
-/// Creates a new hash map with the specified capacity.
-pub fn linear_map_with_capacity<K:Eq + Hash,V>(
- initial_capacity: uint) -> HashMap<K, V> {
- let mut r = rand::task_rng();
- linear_map_with_capacity_and_keys(r.gen(), r.gen(),
- initial_capacity)
-}
-
-fn linear_map_with_capacity_and_keys<K:Eq + Hash,V>(
- k0: u64, k1: u64,
- initial_capacity: uint) -> HashMap<K, V> {
- let cap = num::max(INITIAL_CAPACITY, initial_capacity);
- HashMap {
- k0: k0, k1: k1,
- resize_at: resize_at(cap),
- size: 0,
- buckets: vec::from_fn(cap, |_| None)
- }
+ (capacity * 3) / 4
 }
 
 impl<K:Hash + Eq,V> HashMap<K, V> {
@@ -352,10 +332,28 @@ impl<K: Hash + Eq, V> HashMap<K, V> {
  HashMap::with_capacity(INITIAL_CAPACITY)
  }
 
- /// Create an empty HashMap with space for at least `n` elements in
- /// the hash table.
+ /// Create an empty HashMap with space for at least `capacity`
+ /// elements in the hash table.
  pub fn with_capacity(capacity: uint) -> HashMap<K, V> {
- linear_map_with_capacity(capacity)
+ let mut r = rand::task_rng();
+ HashMap::with_capacity_and_keys(r.gen(), r.gen(), capacity)
+ }
+
+ /// Create an empty HashMap with space for at least `capacity`
+ /// elements, using `k0` and `k1` as the keys.
+ ///
+ /// Warning: `k0` and `k1` are normally randomly generated, and
+ /// are designed to allow HashMaps to be resistant to attacks that
+ /// cause many collisions and very poor performance. Setting them
+ /// manually using this function can expose a DoS attack vector.
+ pub fn with_capacity_and_keys(k0: u64, k1: u64, capacity: uint) -> HashMap<K, V> {
+ let cap = num::max(INITIAL_CAPACITY, capacity);
+ HashMap {
+ k0: k0, k1: k1,
+ resize_at: resize_at(cap),
+ size: 0,
+ buckets: vec::from_fn(cap, |_| None)
+ }
  }
 
  /// Reserve space for at least `n` elements in the hash table.
@@ -844,7 +842,7 @@ mod test_map {
 
  #[test]
  fn test_insert_conflicts() {
- let mut m = linear_map_with_capacity(4);
+ let mut m = HashMap::with_capacity(4);
  assert!(m.insert(1, 2));
  assert!(m.insert(5, 3));
  assert!(m.insert(9, 4));
@@ -855,7 +853,7 @@ mod test_map {
 
  #[test]
  fn test_conflict_remove() {
- let mut m = linear_map_with_capacity(4);
+ let mut m = HashMap::with_capacity(4);
  assert!(m.insert(1, 2));
  assert!(m.insert(5, 3));
  assert!(m.insert(9, 4));
@@ -866,7 +864,7 @@ mod test_map {
 
  #[test]
  fn test_is_empty() {
- let mut m = linear_map_with_capacity(4);
+ let mut m = HashMap::with_capacity(4);
  assert!(m.insert(1, 2));
  assert!(!m.is_empty());
  assert!(m.remove(&1));
@@ -927,7 +925,7 @@ mod test_map {
 
  #[test]
  fn test_iterate() {
- let mut m = linear_map_with_capacity(4);
+ let mut m = HashMap::with_capacity(4);
  foreach i in range(0u, 32) {
  assert!(m.insert(i, i*2));
  }