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simpleHamt.go
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simpleHamt.go
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package main
import (
"fmt"
)
type HamtKey interface {
Equal(HamtKey) bool
Hash() uint64
}
const bitsPerLevel = 6
const valuesPerLevel = 1 << bitsPerLevel
const maxDepth = 64 / bitsPerLevel
type CowSet interface {
insert(HamtKey)
// delete(HamtKey)
find(HamtKey) HamtKey
contains(HamtKey) bool
// iterate(func (HamtKey) bool) bool
debugPrint()
dumpStats()
// copy() CowSet
}
func NewCowSet() CowSet {
return new(HamtRoot)
}
type HamtRoot struct {
root HamtNode
gen uint64
}
func (r *HamtRoot) insert(v HamtKey) {
if r.root == nil {
r.root = new(SmallNode)
}
r.root = internalInsert(r.root, v, v.Hash(), 0, true)
}
func (r *HamtRoot) find(v HamtKey) HamtKey {
if r.root != nil {
return internalFind(r.root, v, v.Hash(), 0)
} else {
return nil
}
}
func (n *HamtRoot) contains(v HamtKey) bool {
return n.find(v) != nil
}
type HamtNode interface {
// generation() uint64
width() int
childAtIndex(int) interface{}
setChildAtIndex(int, interface{})
iterableChildren() []interface{}
copy() HamtNode
copyForGrowth() HamtNode
}
func indexForDepth(h uint64, d int) int {
return int((h >> (d * bitsPerLevel)) % valuesPerLevel)
}
func newNodeWithValues(v1 HamtKey, v2 HamtKey, d int) HamtNode {
result := new(SmallNode)
i1 := indexForDepth(v1.Hash(), d)
i2 := indexForDepth(v2.Hash(), d)
if i1 != i2 {
result.setChildAtIndex(i1, v1)
result.setChildAtIndex(i2, v2)
} else if d < maxDepth {
result.setChildAtIndex(i1, newNodeWithValues(v1, v2, d+1))
} else {
// At max depth, we map colliding values into an array
result.setChildAtIndex(i1, []HamtKey{v1, v2})
}
return result
}
func internalInsert(n HamtNode, v HamtKey, h uint64, d int, overwrite bool) HamtNode {
index := indexForDepth(h, d)
switch c := n.childAtIndex(index).(type) {
case HamtNode:
// There is a node in the spot we need, we ask that node to insert this value as a child
newChild := internalInsert(c, v, h, d+1, overwrite)
if newChild == c {
// The new child was same as the old child, the insert must not have been
// necessary, just return the same Node object we started with.
return n
} else {
// We've got a new node for this child slot, create a new node at this
// level, and insert the new child node.
newNode := n.copy()
newNode.setChildAtIndex(index, newChild)
return newNode
}
case HamtKey:
// There's already a value in the slot we want, first check to see if it's equal to the existing value
if v.Equal(c) {
if overwrite {
// Create a new node with the new value replacing the old value
newNode := n.copy()
newNode.setChildAtIndex(index, v)
return newNode
} else {
// We aren't overwriting existing values, so just return the same
// node we started with
return n
}
} else {
// There is a value in the slot we want, but it's not equal to the new
// value, we need to create a new node that has both values as children
newNode := n.copy()
newNode.setChildAtIndex(index, newNodeWithValues(v, c, d+1))
return newNode
}
case []HamtKey:
fmt.Println("COLLISION")
return nil
case nil:
// There is no value in the slot we need, so we can just
// store the value as a child
newNode := n.copyForGrowth()
newNode.setChildAtIndex(index, v)
return newNode
default:
fmt.Println("PANIC")
return nil
}
// // We have a hash collision at the maximum depth in the tree. We use an array instead
// // of a Node to collect all of the colliding children. This seems like it might be
// // expensive, but remember that it only happens in the case of a 64-bit hash collision...
// if n.nodeMap&(1<<index) != 0 {
// // At max depth, a set bit in the nodeMap means we've already had a collision before
// // and there is a slice stored where we'd normally put a node
// previousCollisions := n.children[index].([]HamtKey)
// duplicateIndex := -1
//
// for ci, cv := range previousCollisions {
// if cv.Equal(v) {
// duplicateIndex = ci
// }
// }
//
// if duplicateIndex > 0 {
// // we found the value we were looking for
// if overwrite {
// // Return a new node with a new slice in the hash slot, but with
// // the new value in place of the old value
// newNode := *n
// newSlice := make([]HamtKey, len(previousCollisions))
// copy(newSlice, previousCollisions)
// newSlice[duplicateIndex] = v
// newNode.children[index] = newSlice
//
// totalNodesByWidth[bits.OnesCount64(newNode.childMap)]++
// return &newNode
// } else {
// // Value's already where we expect it, no updates needed, just return the same node
// return n
// }
// } else {
// // The new value isn't already in the array, we can just append it
// newNode := *n
// newNode.children[index] = append(previousCollisions, v)
//
// totalNodesByWidth[bits.OnesCount64(newNode.childMap)]++
// return &newNode
// }
// } else {
// // There is already a value in the slot we want
// existingValue := n.children[index].(HamtKey)
//
// // First check to see if it's equal to the existing value
// if v.Equal(existingValue) {
// if overwrite {
// // Create a new node with the new value replacing the old value
// newNode := *n
// newNode.children[index] = v
//
// totalNodesByWidth[bits.OnesCount64(newNode.childMap)]++
// return &newNode
// } else {
// // We aren't overwriting existing values, so just return the same
// // node we started with
// return n
// }
// } else {
// // There is a value in the slot we want, but it's not equal to the new
// // value, we need to create a slice that has both values as children
// newNode := *n
// newNode.nodeMap |= (1 << index)
// newNode.children[index] = []HamtKey{existingValue, v}
//
// totalNodesByWidth[bits.OnesCount64(newNode.childMap)]++
// return &newNode
// }
// }
// }
}
// func (n *HamtNode) delete(v HamtKey) *HamtNode {
// result := n.internalDelete(v, 0)
//
// if result == nil {
// result = new(HamtNode)
// }
//
// return result
// }
//
// func (n *HamtNode) internalDelete(v HamtKey, d uint64) *HamtNode {
// index := indexForDepth(v, d)
//
// if n.childMap&(1<<index) == 0 {
// // The value in question doesn't exist, just return the unchanged node
// return n
// } else if d < maxDepth {
// if n.nodeMap&(1<<index) != 0 {
// // The value is in a subnode, ask it to handle the deletion
// newChild := n.children[index].(*HamtNode).internalDelete(v, d+1)
//
// if n.children[index] == newChild {
// // The new child was same as the old child, the delete must not have been
// // necessary, just return the same Node object we started with.
// return n
// } else {
// if n.children[index] == newChild {
// // The new child was same as the old child, the insert must not have been
// // necessary, just return the same Node object we started with.
// return n
// } else {
// // We've got a new node for this index, create a new node at this
// // level, and insert the new node.
// newNode := *n
// newNode.children[index] = newChild
//
// return &newNode
// }
//
//
// }
func internalFind(n HamtNode, v HamtKey, h uint64, d int) HamtKey {
index := indexForDepth(h, d)
switch c := n.childAtIndex(index).(type) {
case HamtNode:
return internalFind(c, v, h, d+1)
case HamtKey:
if c.Equal(v) {
return c
} else {
return nil
}
case []HamtKey:
for _, cv := range c {
if cv.Equal(v) {
return cv
}
}
return nil
default:
return nil
}
}