builtin: a very early version of the hashmap

vlib/builtin/hashmap.v

@@ -0,0 +1,80 @@
+// Copyright (c) 2019 Alexander Medvednikov. All rights reserved.
+// Use of this source code is governed by an MIT license
+// that can be found in the LICENSE file.
+
+module builtin
+
+/*
+	This is work in progress.
+	A very early test version of the hashmap with a fixed size.
+	Only works with string keys and int values for now.
+*/
+
+import math
+
+struct hashmap {
+	cap          int
+	keys         []string
+	table        []hashmapentry
+	elm_size int
+pub:
+	nr_collisions int
+}
+
+struct hashmapentry {
+        key string
+        val int
+        next &hashmapentry  // linked list for collisions
+}
+
+const (
+	min_cap = 2 << 10
+	max_cap = 2 << 20
+)
+
+fn new_hashmap(planned_nr_items int) hashmap {
+	mut cap := planned_nr_items * 3
+	if cap < min_cap {
+		cap = min_cap
+	}	
+	if cap > max_cap {
+		cap = max_cap
+	}	
+	return hashmap{
+		cap: cap
+		elm_size: 4
+		table: _make(cap, cap, sizeof(hashmapentry))
+	}	
+}	
+
+fn (m mut hashmap) set(key string, val int) {
+	hash := int(math.abs(key.hash()))
+	idx := hash % m.cap
+	if m.table[idx].key.len != 0 {
+		//println('\nset() idx=$idx key="$key" hash="$hash" val=$val')
+		m.nr_collisions++
+		//println('collision:' + m.table[idx].key)
+		mut e := &m.table[idx]
+		for e.next != 0 {
+			e = e.next
+		}	
+		e.next = &hashmapentry{key, val, 0}
+	} else {
+		m.table[idx] = hashmapentry{key, val, 0}
+	}
+}	
+
+fn (m mut hashmap) get(key string) int {
+	hash := int(math.abs(key.hash()))
+	idx := hash % m.cap
+	mut e := &m.table[idx]
+	for e.next != 0 { // todo unsafe {
+		if e.key == key {
+			return e.val
+		}	
+		e = e.next
+	}	
+	return e.val
+}
+
+