diff --git a/std/hash_map.zig b/std/hash_map.zig
new file mode 100644
index 0000000000..74efc74363
--- /dev/null
+++ b/std/hash_map.zig
@@ -0,0 +1,262 @@
+const assert = @import("index.zig").assert;
+const math = @import("math.zig");
+const mem = @import("mem.zig");
+const Allocator = mem.Allocator;
+
+const want_modification_safety = !@compile_var("is_release");
+const debug_u32 = if (want_modification_safety) void else u32;
+
+pub struct HashMap(K: type, V: type, hash: fn(key: K)->u32, eql: fn(a: K, b: K)->bool) {
+    entries: []Entry,
+    size: isize,
+    max_distance_from_start_index: isize,
+    allocator: &Allocator,
+    // this is used to detect bugs where a hashtable is edited while an iterator is running.
+    modification_count: debug_u32,
+
+    const Self = HashMap(K, V, hash, eql);
+
+    pub struct Entry {
+        used: bool,
+        distance_from_start_index: isize,
+        key: K,
+        value: V,
+    }
+
+    pub struct Iterator {
+        hm: &Self,
+        // how many items have we returned
+        count: isize,
+        // iterator through the entry array
+        index: isize,
+        // used to detect concurrent modification
+        initial_modification_count: debug_u32,
+
+        pub fn next(it: &Iterator) -> ?&Entry {
+            if (want_modification_safety) {
+                assert(it.initial_modification_count == it.hm.modification_count); // concurrent modification
+            }
+            if (it.count >= it.hm.size) return null;
+            while (it.index < it.hm.entries.len; it.index += 1) {
+                const entry = &it.hm.entries[it.index];
+                if (entry.used) {
+                    it.index += 1;
+                    it.count += 1;
+                    return entry;
+                }
+            }
+            unreachable{} // no next item
+        }
+    };
+    
+    pub fn init(hm: &Self, allocator: &Allocator, capacity: isize) {
+        assert(capacity > 0);
+        hm.allocator = allocator;
+        hm.init_capacity(capacity);
+    }
+
+    pub fn deinit(hm: &Self) {
+        free(_entries);
+    }
+
+    pub fn clear(hm: &Self) {
+        for (hm.entries) |*entry| {
+            entry.used = false;
+        }
+        hm.size = 0;
+        hm.max_distance_from_start_index = 0;
+        hm.increment_modification_count();
+    }
+
+    pub fn put(hm: &Self, key: K, value: V) {
+        hm.increment_modification_count();
+        hm.internal_put(key, value);
+
+        // if we get too full (60%), double the capacity
+        if (hm.size * 5 >= hm.entries.len * 3) {
+            const old_entries = hm.entries;
+            hm.init_capacity(hm.entries.len * 2);
+            // dump all of the old elements into the new table
+            for (old_entries) |*old_entry| {
+                if (old_entry.used) {
+                    hm.internal_put(old_entry.key, old_entry.value);
+                }
+            }
+            hm.allocator.free(hm.allocator, ([]u8)(old_entries));
+        }
+    }
+
+    pub fn get(hm: &Self, key: K) {
+        return internal_get(key);
+    }
+
+    pub fn remove(hm: &Self, key: K) {
+        hm.increment_modification_count();
+        const start_index = hm.key_to_index(key);
+        {var roll_over: isize = 0; while (roll_over <= hm.max_distance_from_start_index; roll_over += 1) {
+            const index = (start_index + roll_over) % hm.entries.len;
+            const entry = &hm.entries[index];
+
+            assert(entry.used); // key not found
+
+            if (!eql(entry.key, key)) continue;
+
+            while (roll_over < hm.entries.len; roll_over += 1) {
+                const next_index = (start_index + roll_over + 1) % hm.entries.len;
+                const next_entry = &hm.entries[next_index];
+                if (!next_entry.used || next_entry.distance_from_start_index == 0) {
+                    entry.used = false;
+                    hm.size -= 1;
+                    return;
+                }
+                *entry = *next_entry;
+                entry.distance_from_start_index -= 1;
+                entry = next_entry;
+            }
+            unreachable{} // shifting everything in the table
+        }}
+        unreachable{} // key not found
+    }
+
+    pub fn entry_iterator(hm: &Self) -> Iterator {
+        return Iterator {
+            .hm = hm,
+            .count = 0,
+            .index = 0,
+            .initial_modification_count = hm.modification_count,
+        };
+    }
+
+    fn init_capacity(hm: &Self, capacity: isize) {
+        hm.capacity = capacity;
+        hm.entries = ([]Entry)(hm.allocator.alloc(hm.allocator, capacity * @sizeof(Entry)));
+        hm.size = 0;
+        hm.max_distance_from_start_index = 0;
+        for (hm.entries) |*entry| {
+            entry.used = false;
+        }
+    }
+
+    fn increment_modification_count(hm: &Self) {
+        if (want_modification_safety) {
+            hm.modification_count += 1;
+        }
+    }
+
+    fn internal_put(hm: &Self, K orig_key, V orig_value) {
+        var key = orig_key;
+        var value = orig_value;
+        const start_index = key_to_index(key);
+        var roll_over: isize = 0;
+        var distance_from_start_index: isize = 0;
+        while (roll_over < hm.entries.len; {roll_over += 1; distance_from_start_index += 1}) {
+            const index = (start_index + roll_over) % hm.entries.len;
+            const entry = &hm.entries[index];
+
+            if (entry.used && !eql(entry.key, key)) {
+                if (entry.distance_from_start_index < distance_from_start_index) {
+                    // robin hood to the rescue
+                    const tmp = *entry;
+                    hm.max_distance_from_start_index = math.max(isize)(
+                        hm.max_distance_from_start_index, distance_from_start_index);
+                    *entry = Entry {
+                        .used = true,
+                        .distance_from_start_index = distance_from_start_index,
+                        .key = key,
+                        .value = value,
+                    };
+                    key = tmp.key;
+                    value = tmp.value;
+                    distance_from_start_index = tmp.distance_from_start_index;
+                }
+                continue;
+            }
+
+            if (!entry.used) {
+                // adding an entry. otherwise overwriting old value with
+                // same key
+                hm.size += 1;
+            }
+
+            hm.max_distance_from_start_index = math.max(isize)(distance_from_start_index, hm.max_distance_from_start_index);
+            *entry = {
+                .used = true,
+                .distance_from_start_index = distance_from_start_index,
+                .key = key,
+                .value = value,
+            };
+            return;
+        }
+        unreachable{} // put into a full map
+    }
+
+    fn internal_get(hm: &Self, key: K) -> ?&Entry {
+        const start_index = key_to_index(key);
+        {var roll_over: isize = 0; while (roll_over <= hm.max_distance_from_start_index; roll_over += 1) {
+            const index = (start_index + roll_over) % hm.entries.len;
+            const entry = &hm.entries[index];
+
+            if (!entry.used) return null;
+            if (eql(entry.key, key)) return entry;
+        }}
+        return null;
+    }
+
+    Entry *internal_get(const K &key) const {
+        int start_index = key_to_index(key);
+        for (int roll_over = 0; roll_over <= _max_distance_from_start_index; roll_over += 1) {
+            int index = (start_index + roll_over) % _capacity;
+            Entry *entry = &_entries[index];
+
+            if (!entry->used)
+                return NULL;
+
+            if (EqualFn(entry->key, key))
+                return entry;
+        }
+        return NULL;
+    }
+
+    fn key_to_index(hm: &Self, key: K) -> isize {
+        return isize(hash(key)) % hm.entries.len;
+    }
+}
+
+var global_allocator = Allocator {
+    .alloc = global_alloc,
+    .realloc = global_realloc,
+    .free = global_free,
+    .context = null,
+};
+
+var some_mem: [200]u8 = undefined;
+var some_mem_index: isize = 0;
+
+fn global_alloc(self: &Allocator, n: isize) -> %[]u8 {
+    const result = some_mem[some_mem_index ... some_mem_index + n];
+    some_mem_index += n;
+    return result;
+}
+
+fn global_realloc(self: &Allocator, old_mem: []u8, new_size: isize) -> %[]u8 {
+    const result = %return global_alloc(self, new_size);
+    @memcpy(result.ptr, old_mem.ptr, old_mem.len);
+    return result;
+}
+
+fn global_free(self: &Allocator, old_mem: []u8) {
+}
+
+#attribute("test")
+fn basic_hash_map_test() {
+    var map: HashMap(i32, i32, hash_i32, eql_i32);
+    map.init(&global_allocator, 4);
+    defer map.deinit();
+}
+
+fn hash_i32(x: i32) -> u32 {
+    *(&u32)(&x)
+}
+fn eql_i32(a: i32, b: i32) -> bool {
+    a == b
+}
diff --git a/std/io.zig b/std/io.zig
index 07a480f096..3f904236eb 100644
--- a/std/io.zig
+++ b/std/io.zig
@@ -69,7 +69,7 @@ pub struct OutStream {
         const dest_space_left = os.buffer.len - os.index;
 
         while (src_bytes_left > 0) {
-            const copy_amt = math.min_isize(dest_space_left, src_bytes_left);
+            const copy_amt = math.min(isize)(dest_space_left, src_bytes_left);
             @memcpy(&os.buffer[os.index], &bytes[src_index], copy_amt);
             os.index += copy_amt;
             if (os.index == os.buffer.len) {
diff --git a/std/math.zig b/std/math.zig
index 44c440105e..39f982b361 100644
--- a/std/math.zig
+++ b/std/math.zig
@@ -26,7 +26,10 @@ pub fn f64_is_inf(f: f64) -> bool {
     f == f64_get_neg_inf() || f == f64_get_pos_inf()
 }
 
-pub fn min_isize(x: isize, y: isize) -> isize {
+pub fn min(T: type)(x: T, y: T) -> T {
     if (x < y) x else y
 }
 
+pub fn max(T: type)(x: T, y: T) -> T {
+    if (x > y) x else y
+}