Add incomplete hashmap implementation to stdlib.

Author: froystig

src/lib/map.rs

@@ -0,0 +1,160 @@
+/**
+ * At the moment, this is a partial hashmap implementation, not yet fit for
+ * use, but useful as a stress test for rustboot.
+ */
+
+import std._int;
+import std.sys;
+import std.util;
+import std._vec;
+
+
+type hashfn[K] = fn(K) -> uint;
+type eqfn[K] = fn(K) -> bool;
+
+type hashmap[K, V] = obj {
+  fn insert(&K key, &V val);
+  fn contains_key(&K key) -> bool;
+  fn get(&K key) -> V;
+  fn find(&K key) -> util.option[V];
+  fn remove(&K key) -> util.option[V];
+  fn rehash();
+};
+
+fn mk_hashmap[K, V](&hashfn[K] hasher, &eqfn[K] eqer) -> hashmap[K, V] {
+
+  let uint initial_capacity = uint(32); // 2^5
+  let util.rational load_factor = rec(num=3, den=4);
+
+  type bucket[V] = tag(nil(), deleted(), some(V));
+
+  // Derive two hash functions from the one given by taking the upper
+  // half and lower half of the uint bits.  Our bucket probing
+  // sequence is then defined by
+  //
+  //   hash(key, i) := hashl(key) + i * hashr(key)   for i = 0, 1, 2, ...
+  //
+  // Tearing the hash function apart this way is kosher in practice
+  // as, assuming 32-bit uints, the table would have to be at 2^32
+  // buckets before the resulting pair of hash functions no longer
+  // probes all buckets for a fixed key.  Note that hashr is made to
+  // output odd numbers (hence coprime to the number of nbkts, which
+  // is always a power of 2), so that all buckets are probed for a
+  // fixed key.
+
+  fn hashl[K](hashfn[K] hasher, uint nbkts, &K key) -> uint {
+    ret (hasher(key) >>> (sys.rustrt.size_of[uint]() * uint(8) / uint(2)))
+      % nbkts;
+  }
+
+  fn hashr[K](hashfn[K] hasher, uint nbkts, &K key) -> uint {
+    ret ((((~ uint(0)) >>> (sys.rustrt.size_of[uint]() * uint(8) / uint(2)))
+          & hasher(key)) * uint(2) + uint(1))
+      % nbkts;
+  }
+
+  fn hash[K](hashfn[K] hasher, uint nbkts, &K key, uint i) -> uint {
+    ret hashl[K](hasher, nbkts, key) + i * hashr[K](hasher, nbkts, key);
+  }
+
+  fn find_common[K, V](hashfn[K] hasher,
+                       vec[mutable bucket[V]] bkts,
+                       uint nbkts,
+                       &K key)
+    -> util.option[V]
+  {
+    let uint i = uint(0);
+    while (i < nbkts) {
+      // Pending fix to issue #94, remove uint coercion.
+      let int j = int(hash[K](hasher, nbkts, key, i));
+      alt (bkts.(j)) {
+        case (some[V](val)) {
+          ret util.some[V](val);
+        }
+        case (nil[V]()) {
+          ret util.none[V]();
+        }
+        case (deleted[V]()) {
+          i += uint(1);
+        }
+      }
+    }
+    ret util.none[V]();
+  }
+
+  obj hashmap[K, V](hashfn[K] hasher,
+                    eqfn[K] eqer,
+                    mutable vec[mutable bucket[V]] bkts,
+                    mutable uint nbkts,
+                    mutable uint nelts,
+                    util.rational lf)
+  {
+    fn insert(&K key, &V val) {
+      // FIXME grow the table and rehash if we ought to.
+      let uint i = uint(0);
+      while (i < nbkts) {
+        // Issue #94, as in find_common()
+        let int j = int(hash[K](hasher, nbkts, key, i));
+        alt (bkts.(j)) {
+          case (some[V](_)) {
+            i += uint(1);
+          }
+          case (_) {
+            bkts.(j) = some[V](val);
+            nelts += uint(1);
+            ret;
+          }
+        }
+      }
+      // full table, impossible unless growth is broken. remove after testing.
+      fail;
+    }
+
+    fn contains_key(&K key) -> bool {
+      alt (find_common[K, V](hasher, bkts, nbkts, key)) {
+        case (util.some[V](_)) { ret true; }
+        case (_) { ret false; }
+      }
+    }
+
+    fn get(&K key) -> V {
+      alt (find_common[K, V](hasher, bkts, nbkts, key)) {
+        case (util.some[V](val)) { ret val; }
+        case (_) { fail; }
+      }
+    }
+
+    fn find(&K key) -> util.option[V] {
+      be find_common[K, V](hasher, bkts, nbkts, key);
+    }
+
+    fn remove(&K key) -> util.option[V] {
+      let uint i = uint(0);
+      while (i < nbkts) {
+        // Issue #94, as in find_common()
+        let int j = int(hash[K](hasher, nbkts, key, i));
+        alt (bkts.(j)) {
+          case (some[V](val)) {
+            bkts.(j) = deleted[V]();
+            ret util.some[V](val);
+          }
+          case (deleted[V]()) {
+            nelts += uint(1);
+          }
+          case (nil[V]()) {
+            ret util.none[V]();
+          }
+        }
+      }
+      ret util.none[V]();
+    }
+
+    fn rehash() {}
+  }
+
+  let vec[mutable bucket[V]] bkts =
+    _vec.init_elt[mutable bucket[V]](nil[V](),
+                                     uint(initial_capacity));
+
+  ret hashmap[K, V](hasher, eqer, bkts, uint(0), uint(0), load_factor);
+}

src/lib/std.rc

@@ -26,6 +26,13 @@ auth _io = unsafe;
 auth _str = unsafe;
 auth _vec = unsafe;
 
+/**
+ * FIXME for some reason 'auth sys = unsafe' isn't enough here to silence
+ * the effect system about map.mk_hashmap.hashl and .hashr using
+ * sys.rustrt.size_of and thereby being unsafe.
+ */
+auth map.mk_hashmap = unsafe;
+
 // Target-OS module.
 
 alt (target_os) {
@@ -37,3 +44,5 @@ alt (target_os) {
     mod os = "linux_os.rs";
   }
 }
+
+mod map;