From 8800413f52f427d41da193f7139e8d1a5038c836 Mon Sep 17 00:00:00 2001
From: Niko Matsakis <niko@alum.mit.edu>
Date: Thu, 26 Jul 2012 16:09:22 -0700
Subject: [PATCH] wip: add a sendable hashmap to stdlib

caveats:
- not efficient nor heavily tested
- API subject to change and currently incompatible with map
---
 src/libstd/send_map.rs | 345 +++++++++++++++++++++++++++++++++++++++++
 src/libstd/std.rc      |   1 +
 2 files changed, 346 insertions(+)
 create mode 100644 src/libstd/send_map.rs

diff --git a/src/libstd/send_map.rs b/src/libstd/send_map.rs
new file mode 100644
index 000000000000..90d99adad896
--- /dev/null
+++ b/src/libstd/send_map.rs
@@ -0,0 +1,345 @@
+/*!
+
+Sendable hash maps.  Very much a work in progress.
+
+*/
+
+
+/**
+ * A function that returns a hash of a value
+ *
+ * The hash should concentrate entropy in the lower bits.
+ */
+type hashfn<K> = pure fn~(K) -> uint;
+type eqfn<K> = pure fn~(K, K) -> bool;
+
+/// Open addressing with linear probing.
+mod linear {
+    export linear_map, linear_map_with_capacity;
+
+    const initial_capacity: uint = 32u; // 2^5
+    type bucket<K,V> = {hash: uint, key: K, value: V};
+    enum linear_map<K,V> {
+        linear_map_({
+            hashfn: pure fn~(x: &K) -> uint,
+            eqfn: pure fn~(x: &K, y: &K) -> bool,
+            resize_at: uint,
+            size: uint,
+            buckets: ~[option<bucket<K,V>>]})
+    }
+
+    // FIXME(#2979) -- with #2979 we could rewrite found_entry
+    // to have type option<&bucket<K,V>> which would be nifty
+    enum search_result {
+        found_entry(uint), found_hole(uint), table_full
+    }
+
+    fn resize_at(capacity: uint) -> uint {
+        ((capacity as float) * 3. / 4.) as uint
+    }
+
+    fn linear_map<K,V>(
+        +hashfn: pure fn~(x: &K) -> uint,
+        +eqfn: pure fn~(x: &K, y: &K) -> bool) -> linear_map<K,V> {
+
+        linear_map_with_capacity(hashfn, eqfn, 32)
+    }
+
+    fn linear_map_with_capacity<K,V>(
+        +hashfn: pure fn~(x: &K) -> uint,
+        +eqfn: pure fn~(x: &K, y: &K) -> bool,
+        initial_capacity: uint) -> linear_map<K,V> {
+
+        linear_map_({
+            hashfn: hashfn,
+            eqfn: eqfn,
+            resize_at: resize_at(initial_capacity),
+            size: 0,
+            buckets: vec::from_fn(initial_capacity, |_i| none)})
+    }
+
+    // FIXME(#2979) would allow us to use region type for k
+    unsafe fn borrow<K>(&&k: K) -> &K {
+        let p: *K = ptr::addr_of(k);
+        p as &K
+    }
+
+    impl private_const_methods<K,V> for &const linear_map<K,V> {
+        #[inline(always)]
+        pure fn to_bucket(h: uint) -> uint {
+            // FIXME(#3041) borrow a more sophisticated technique here from
+            // Gecko, for example borrowing from Knuth, as Eich so
+            // colorfully argues for here:
+            // https://bugzilla.mozilla.org/show_bug.cgi?id=743107#c22
+            h % self.buckets.len()
+        }
+
+        #[inline(always)]
+        pure fn next_bucket(idx: uint, len_buckets: uint) -> uint {
+            let n = (idx + 1) % len_buckets;
+            unsafe{ // argh. log not considered pure.
+                #debug["next_bucket(%?, %?) = %?", idx, len_buckets, n];
+            }
+            ret n;
+        }
+
+        #[inline(always)]
+        pure fn bucket_sequence(hash: uint, op: fn(uint) -> bool) -> uint {
+            let start_idx = self.to_bucket(hash);
+            let len_buckets = self.buckets.len();
+            let mut idx = start_idx;
+            loop {
+                if !op(idx) {
+                    ret idx;
+                }
+                idx = self.next_bucket(idx, len_buckets);
+                if idx == start_idx {
+                    ret start_idx;
+                }
+            }
+        }
+
+        #[inline(always)]
+        pure fn bucket_for_key(
+            buckets: &[option<bucket<K,V>>],
+            k: &K) -> search_result {
+
+            let hash = self.hashfn(k);
+            self.bucket_for_key_with_hash(buckets, hash, k)
+        }
+
+        #[inline(always)]
+        pure fn bucket_for_key_with_hash(
+            buckets: &[option<bucket<K,V>>],
+            hash: uint,
+            k: &K) -> search_result {
+
+            let _ = for self.bucket_sequence(hash) |i| {
+                alt buckets[i] {
+                  some(bkt) {
+                    if bkt.hash == hash && self.eqfn(k, &bkt.key) {
+                        ret found_entry(i);
+                    }
+                  }
+                  none => {
+                    ret found_hole(i);
+                  }
+                }
+            };
+            ret table_full;
+        }
+    }
+
+    impl private_mut_methods<K,V> for &mut linear_map<K,V> {
+        /// Expands the capacity of the array and re-inserts each
+        /// of the existing buckets.
+        fn expand() {
+            let old_capacity = self.buckets.len();
+            let new_capacity = old_capacity * 2;
+            self.resize_at = ((new_capacity as float) * 3.0 / 4.0) as uint;
+
+            let mut old_buckets = vec::from_fn(new_capacity, |_i| none);
+            self.buckets <-> old_buckets;
+
+            for uint::range(0, old_capacity) |i| {
+                let mut bucket = none;
+                bucket <-> old_buckets[i];
+                if bucket.is_some() {
+                    self.insert_bucket(bucket);
+                }
+            }
+        }
+
+        fn insert_bucket(+bucket: option<bucket<K,V>>) {
+            let {hash, key, value} <- option::unwrap(bucket);
+            let _ = self.insert_internal(hash, key, value);
+        }
+
+        /// Inserts the key value pair into the buckets.
+        /// Assumes that there will be a bucket.
+        /// True if there was no previous entry with that key
+        fn insert_internal(hash: uint, +k: K, +v: V) -> bool {
+            alt self.bucket_for_key_with_hash(self.buckets, hash,
+                                              unsafe{borrow(k)}) {
+              table_full => {fail ~"Internal logic error";}
+              found_hole(idx) {
+                #debug["insert fresh (%?->%?) at idx %?, hash %?",
+                       k, v, idx, hash];
+                self.buckets[idx] = some({hash: hash, key: k, value: v});
+                self.size += 1;
+                ret true;
+              }
+              found_entry(idx) => {
+                #debug["insert overwrite (%?->%?) at idx %?, hash %?",
+                       k, v, idx, hash];
+                self.buckets[idx] = some({hash: hash, key: k, value: v});
+                ret false;
+              }
+            }
+        }
+    }
+
+    impl mut_methods<K,V> for &mut linear_map<K,V> {
+        fn insert(+k: K, +v: V) -> bool {
+            if self.size >= self.resize_at {
+                // n.b.: We could also do this after searching, so
+                // that we do not resize if this call to insert is
+                // simply going to update a key in place.  My sense
+                // though is that it's worse to have to search through
+                // buckets to find the right spot twice than to just
+                // resize in this corner case.
+                self.expand();
+            }
+
+            let hash = self.hashfn(unsafe{borrow(k)});
+            self.insert_internal(hash, k, v)
+        }
+
+        fn remove(k: &K) -> bool {
+            // Removing from an open-addressed hashtable
+            // is, well, painful.  The problem is that
+            // the entry may lie on the probe path for other
+            // entries, so removing it would make you think that
+            // those probe paths are empty.
+            //
+            // To address this we basically have to keep walking,
+            // re-inserting entries we find until we reach an empty
+            // bucket.  We know we will eventually reach one because
+            // we insert one ourselves at the beginning (the removed
+            // entry).
+            //
+            // I found this explanation elucidating:
+            // http://www.maths.lse.ac.uk/Courses/MA407/del-hash.pdf
+
+            let mut idx = alt self.bucket_for_key(self.buckets, k) {
+              table_full | found_hole(_) => {
+                ret false;
+              }
+              found_entry(idx) => {
+                idx
+              }
+            };
+
+            let len_buckets = self.buckets.len();
+            self.buckets[idx] = none;
+            idx = self.next_bucket(idx, len_buckets);
+            while self.buckets[idx].is_some() {
+                let mut bucket = none;
+                bucket <-> self.buckets[idx];
+                self.insert_bucket(bucket);
+                idx = self.next_bucket(idx, len_buckets);
+            }
+            ret true;
+        }
+    }
+
+    impl private_imm_methods<K,V> for &linear_map<K,V> {
+        fn search(hash: uint, op: fn(x: &option<bucket<K,V>>) -> bool) {
+            let _ = self.bucket_sequence(hash, |i| op(&self.buckets[i]));
+        }
+    }
+
+    impl const_methods<K,V> for &const linear_map<K,V> {
+        fn size() -> uint {
+            self.size
+        }
+
+        fn contains_key(k: &K) -> bool {
+            alt self.bucket_for_key(self.buckets, k) {
+              found_entry(_) => {true}
+              table_full | found_hole(_) => {false}
+            }
+        }
+    }
+
+    impl const_methods<K,V: copy> for &const linear_map<K,V> {
+        fn find(k: &K) -> option<V> {
+            alt self.bucket_for_key(self.buckets, k) {
+              found_entry(idx) => {
+                alt check self.buckets[idx] {
+                  some(bkt) => {some(copy bkt.value)}
+                }
+              }
+              table_full | found_hole(_) => {
+                none
+              }
+            }
+        }
+
+        fn get(k: &K) -> V {
+            let value = self.find(k);
+            if value.is_none() {
+                fail #fmt["No entry found for key: %?", k];
+            }
+            option::unwrap(value)
+        }
+
+        fn [](k: &K) -> V {
+            self.get(k)
+        }
+    }
+
+    /*
+    FIXME --- #2979 must be fixed to typecheck this
+    impl imm_methods<K,V> for &linear_map<K,V> {
+        fn find_ptr(k: K) -> option<&V> {
+            //XXX this should not type check as written, but it should
+            //be *possible* to typecheck it...
+            self.with_ptr(k, |v| v)
+        }
+    }
+    */
+}
+
+#[test]
+mod test {
+
+    import linear::linear_map;
+
+    pure fn uint_hash(x: &uint) -> uint { *x }
+    pure fn uint_eq(x: &uint, y: &uint) -> bool { *x == *y }
+
+    fn int_linear_map<V>() -> linear_map<uint,V> {
+        ret linear_map(uint_hash, uint_eq);
+    }
+
+    #[test]
+    fn inserts() {
+        let mut m = int_linear_map();
+        assert (&mut m).insert(1, 2);
+        assert (&mut m).insert(2, 4);
+        assert (&m).get(&1) == 2;
+        assert (&m).get(&2) == 4;
+    }
+
+    #[test]
+    fn overwrite() {
+        let mut m = int_linear_map();
+        assert (&mut m).insert(1, 2);
+        assert (&m).get(&1) == 2;
+        assert !(&mut m).insert(1, 3);
+        assert (&m).get(&1) == 3;
+    }
+
+    #[test]
+    fn conflicts() {
+        let mut m = linear::linear_map_with_capacity(uint_hash, uint_eq, 4);
+        assert (&mut m).insert(1, 2);
+        assert (&mut m).insert(5, 3);
+        assert (&mut m).insert(9, 4);
+        assert (&m).get(&9) == 4;
+        assert (&m).get(&5) == 3;
+        assert (&m).get(&1) == 2;
+    }
+
+    #[test]
+    fn conflict_remove() {
+        let mut m = linear::linear_map_with_capacity(uint_hash, uint_eq, 4);
+        assert (&mut m).insert(1, 2);
+        assert (&mut m).insert(5, 3);
+        assert (&mut m).insert(9, 4);
+        assert (&mut m).remove(&1);
+        assert (&m).get(&9) == 4;
+        assert (&m).get(&5) == 3;
+    }
+}
\ No newline at end of file
diff --git a/src/libstd/std.rc b/src/libstd/std.rc
index d6f3bf272340..c1da4b0bd066 100644
--- a/src/libstd/std.rc
+++ b/src/libstd/std.rc
@@ -58,6 +58,7 @@ mod deque;
 mod fun_treemap;
 mod list;
 mod map;
+mod send_map;
 mod rope;
 mod smallintmap;
 mod sort;