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// $G $F.go && $L $F.$A && ./$A.out
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
// ----------------------------------------------------------------------------
// Helper functions
func ASSERT(p bool) {
if !p {
// panic 0;
}
}
// ----------------------------------------------------------------------------
// Implementation of the HashMap
type KeyType interface {
Hash() uint32;
Match(other *KeyType) bool
}
type ValueType interface {
// empty interface
}
type Entry struct {
key *KeyType;
value *ValueType;
}
// Using the Array type below doesn't seem to work
//type Array array [1024] Entry;
type HashMap struct {
map_ *[1024] Entry;
log2_capacity_ uint32;
occupancy_ uint32;
}
func (m *HashMap) capacity() uint32 {
return 1 << m.log2_capacity_;
}
func (m *HashMap) Clear() {
// Mark all entries as empty.
var i uint32 = m.capacity() - 1;
for i > 0 {
m.map_[i].key = nil;
i = i - 1
}
m.occupancy_ = 0
}
func (m *HashMap) Initialize (initial_log2_capacity uint32) {
m.log2_capacity_ = initial_log2_capacity;
m.map_ = new([1024] Entry);
m.Clear();
}
func (m *HashMap) Probe (key *KeyType) *Entry {
ASSERT(key != nil);
var i uint32 = key.Hash() % m.capacity();
ASSERT(0 <= i && i < m.capacity());
ASSERT(m.occupancy_ < m.capacity()); // guarantees loop termination
for m.map_[i].key != nil && !m.map_[i].key.Match(key) {
i++;
if i >= m.capacity() {
i = 0;
}
}
return &m.map_[i];
}
func (m *HashMap) Lookup (key *KeyType, insert bool) *Entry {
// Find a matching entry.
var p *Entry = m.Probe(key);
if p.key != nil {
return p;
}
// No entry found; insert one if necessary.
if insert {
p.key = key;
p.value = nil;
m.occupancy_++;
// Grow the map if we reached >= 80% occupancy.
if m.occupancy_ + m.occupancy_/4 >= m.capacity() {
m.Resize();
p = m.Probe(key);
}
return p;
}
// No entry found and none inserted.
return nil;
}
func (m *HashMap) Resize() {
var hmap *[1024] Entry = m.map_;
var n uint32 = m.occupancy_;
// Allocate a new map of twice the current size.
m.Initialize(m.log2_capacity_ << 1);
// Rehash all current entries.
var i uint32 = 0;
for n > 0 {
if hmap[i].key != nil {
m.Lookup(hmap[i].key, true).value = hmap[i].value;
n = n - 1;
}
i++;
}
}
// ----------------------------------------------------------------------------
// Test code
type Number struct {
x uint32;
}
func (n *Number) Hash() uint32 {
return n.x * 23;
}
func (n *Number) Match(other *KeyType) bool {
// var y *Number = other;
// return n.x == y.x;
return false;
}
func MakeNumber (x uint32) *Number {
var n *Number = new(Number);
n.x = x;
return n;
}
func main() {
//f unc (n int) int { return n + 1; }(1);
//print "HashMap - gri 2/8/2008\n";
var hmap *HashMap = new(HashMap);
hmap.Initialize(0);
var x1 *Number = MakeNumber(1001);
var x2 *Number = MakeNumber(2002);
var x3 *Number = MakeNumber(3003);
// this doesn't work I think...
//hmap.Lookup(x1, true);
//hmap.Lookup(x2, true);
//hmap.Lookup(x3, true);
//print "done\n";
}
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