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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
}
type Array [1024]Entry
type HashMap struct {
map_ *Array
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(Array)
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 *Array = 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() {
// func (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)
_, _, _ = x1, x2, x3
// 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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