12 Commits

Author SHA1 Message Date
5c39182958 refactor: HashTable -> Table, table -> subtable
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2026-04-13 21:11:37 -04:00
2eeff25efd Merge remote-tracking branch 'origin' into refactor/name-bucket-slot-table 2026-04-13 20:54:09 -04:00
6a5b40c097 docs: replaced instances of "bucket" with "table"
- Removed instances of `growthFactor`, as it is unexported.
- Typo in `HashTable.String()`.
2026-04-13 20:49:33 -04:00
867a1d49df feat: sentinel error ErrBadHash (#19)
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## Description

Currently, the errors are not sentinel, and so are hard to test for. This PR makes sure hash collision errors are accounted for.

## Changes

- Add `ErrBadHash`. Happens when there are too many collisions for an item to be added.

### Design Decisions

- Chose to name `ErrBadHash` over `ErrCycle` because the feedbach that the user should be given is to evaluate their hash functions. Cycle collision is a bit esoteric.

## Checklist

- [x] Tests pass
- [x] Docs updated

Reviewed-on: #19
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>
2026-04-14 00:38:11 +00:00
395a3560c7 refactor: constructors, update docs
- NewCustomTable -> NewCustom
- NewTableBy -> NewBy
- NewTable -> New
2026-04-04 12:27:53 +02:00
2fd9da973b refactor: bucket -> table, Table -> HashTable 2026-04-04 12:22:42 +02:00
322d71f0be refactor!: remove MinimumLoad() option (#17)
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## Description

The `cuckoo.MinimumLoad()` option was not a very useful option, and prone to error. By removing the ability to modify it, and setting it to something reasonable (like 5%), we can remove a whole set of errors that the user may stumble into.

## Changes

- Remove `MinimumLoad()` option.
- Privated `DefaultMinimumLoad`.

### Design Decisions

- `DefaultMinimumLoad` should be privated because it is no longer an option. The user should not need to interact with it.

## Checklist

- [x] Tests pass
- [x] Docs updated

Reviewed-on: #17
2026-04-03 14:51:41 +00:00
ed30a4fc7c fix: check-pr-title job has prompt injection (#18)
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## Description

Currently, the `check-pr-title` job has a security vulnerability. If you give the PR a bad title, the job can run arbitrary code.

## Changes

- Fix prompt injection by pulling the PR title as an environment variable.
- Also, restricted the job to only `pull_request` trigger.

### Design Decisions

- It is better to pull out this job into a separate workflow with a unique trigger, but I chose not to because it is currently only one job.

## Checklist

- [x] Tests pass
- [x] Docs updated

Reviewed-on: #18
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>
2026-04-03 14:47:01 +00:00
c834f004a2 chore: no free form issues, 'description'-s to 'placeholders'-s (#16)
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## Description

There were some problems with the roll-out of the issue templates. This PR addresses them.

## Changes

- Disable `blank-issue-enabled`.
- Move all `description` types in the issue templates to `placeholder`.

### Design Decisions

- The `description` fields take up too much space.

## Checklist

- [x] Tests pass
- [x] Docs updated

Reviewed-on: #16
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>
2026-04-03 13:57:03 +00:00
581f26f562 ci: support semantic versioning, conventional commits (#15)
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## Description

Currently, the repository is not well suited for semantic versioning, and hasn't much to support it. This PR adds templates, CI jobs, and configs to simplify its adoption.

## Changes

- Added `FEATURE` and `BUG` issue templates. Also, forbids free-form issues.
- Adds a PR template.
- Adds a CI job to ensure the commit title follows conventional commits.

### Design Decisions

N/A.

## Checklist

- [x] Tests pass
- [x] Docs updated

Reviewed-on: #15
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>
2026-04-03 13:46:05 +00:00
b1ab3a6326 chore: remove ./.claude/settings.json (#14)
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There shouldn't be a global settings folder for Claude in the repository. Also, add final newline to `.gitignore`.

Reviewed-on: #14
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>
2026-03-28 19:52:06 +00:00
36d76d4929 feat: wider fuzz tests, stronger options. (#9)
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- Added all `Option`-s to the fuzz tests.
  - Minimum load is always <=20%.
- Tested all options, and force a panic on all invalid options.
  - Capacity must now be non-negative.
  - Minimum load should be <=20%, but just put it as a recommendation.

Reviewed-on: #9
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>
2026-03-25 01:26:56 +00:00
18 changed files with 315 additions and 202 deletions

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@@ -1,7 +0,0 @@
{
"permissions": {
"allow": [
"Bash(curl -s -w \"\\\\n---HTTP_STATUS:%{http_code}---\" https://raw.githubusercontent.com/kubernetes/kubernetes/master/.markdownlint.yaml)"
]
}
}

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@@ -0,0 +1,26 @@
# yaml-language-server: $schema=https://www.schemastore.org/gitea-issue-forms.json
name: 🐛 Bug Report
about: Report a bug in this project
title: "[BUG]: "
body:
- type: textarea
id: context
attributes:
label: Context
placeholder: What circumstances led to the bug?
validations:
required: true
- type: textarea
id: expected-behavior
attributes:
label: Expected Behavior
placeholder: What did you expect would happen?
validations:
required: true
- type: textarea
id: actual-behavior
attributes:
label: Actual Behavior
placeholder: What happened, and why was it unexpected?
validations:
required: true

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@@ -0,0 +1,37 @@
# 'Feature Request Template' By @cheehwatang
# https://github.com/cheehwatang/.github/blob/master/.github/ISSUE_TEMPLATE/feature_request.yml
#
# yaml-language-server: $schema=https://www.schemastore.org/gitea-issue-forms.json
name: ✨ Feature Request
about: Suggest an idea for this project
title: "[FEATURE]: "
body:
- type: dropdown
attributes:
multiple: false
label: Feature Type
options:
- "✨ New Feature"
- "📝 Documentation"
- "🎨 Style and UI"
- "🔨 Code Refactor"
- "⚡ Performance Improvements"
- "✅ New Test"
validations:
required: true
- type: textarea
id: description
attributes:
label: Description
placeholder: |
Give us a brief description of the feature or enhancement you would
like!
validations:
required: true
- type: textarea
id: additional-information
attributes:
label: Additional Information
placeholder: |
Give us some additional information on the feature request like proposed
solutions, links, screenshots, etc.

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@@ -0,0 +1,2 @@
# yaml-language-server: $schema=https://www.schemastore.org/gitea-issue-config.json
blank_issues_enabled: false

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@@ -0,0 +1,17 @@
---
name: "New Pull Request"
about: "Standard PR template"
title: ""
ref: "main"
---
## Description
## Changes
### Design Decisions
## Checklist
- [ ] Tests pass
- [ ] Docs updated

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@@ -6,6 +6,19 @@ on:
pull_request: pull_request:
jobs: jobs:
check-pr-title:
name: Check PR Title
runs-on: ubuntu-latest
if: github.event_name == 'pull_request'
env:
TITLE: ${{ gitea.event.pull_request.title }}
steps:
- run: |
if ! echo "$TITLE" | grep -qE '^(WIP: )?(feat|fix|docs|chore|ci|test|refactor|perf|build|style|revert)(\(.+\))?(!)?: .+'; then
echo "::error::Pull Request title must follow conventional commits"
exit 1
fi
lint-go: lint-go:
name: Go Lint name: Go Lint
runs-on: ubuntu-latest runs-on: ubuntu-latest

1
.gitignore vendored
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@@ -24,4 +24,3 @@ go.work.sum
# env file # env file
.env .env

103
bucket.go
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@@ -1,103 +0,0 @@
package cuckoo
type entry[K, V any] struct {
key K
value V
}
type slot[K, V any] struct {
entry[K, V]
occupied bool
}
type bucket[K, V any] struct {
hash Hash[K]
slots []slot[K, V]
capacity, size uint64
compare EqualFunc[K]
}
// location determines where in the bucket a certain key would be placed. If the
// capacity is 0, this will panic.
func (b bucket[K, V]) location(key K) uint64 {
return b.hash(key) % b.capacity
}
func (b bucket[K, V]) get(key K) (value V, found bool) {
if b.capacity == 0 {
return
}
slot := b.slots[b.location(key)]
return slot.value, slot.occupied && b.compare(slot.key, key)
}
func (b *bucket[K, V]) drop(key K) (occupied bool) {
if b.capacity == 0 {
return
}
slot := &b.slots[b.location(key)]
if slot.occupied && b.compare(slot.key, key) {
slot.occupied = false
b.size--
return true
}
return false
}
func (b *bucket[K, V]) resize(capacity uint64) {
b.slots = make([]slot[K, V], capacity)
b.capacity = capacity
b.size = 0
}
func (b bucket[K, V]) update(key K, value V) (updated bool) {
if b.capacity == 0 {
return
}
slot := &b.slots[b.location(key)]
if slot.occupied && b.compare(slot.key, key) {
slot.value = value
return true
}
return false
}
func (b *bucket[K, V]) evict(insertion entry[K, V]) (evicted entry[K, V], eviction bool) {
if b.capacity == 0 {
return insertion, true
}
slot := &b.slots[b.location(insertion.key)]
if !slot.occupied {
slot.entry = insertion
slot.occupied = true
b.size++
return
}
if b.compare(slot.key, insertion.key) {
slot.value = insertion.value
return
}
insertion, slot.entry = slot.entry, insertion
return insertion, true
}
func newBucket[K, V any](capacity uint64, hash Hash[K], compare EqualFunc[K]) bucket[K, V] {
return bucket[K, V]{
hash: hash,
capacity: capacity,
compare: compare,
size: 0,
slots: make([]slot[K, V], capacity),
}
}

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@@ -2,7 +2,7 @@ package cuckoo
// An EqualFunc determines whethers two keys are 'equal'. Keys that are 'equal' // An EqualFunc determines whethers two keys are 'equal'. Keys that are 'equal'
// are teated as the same by the [Table]. A good EqualFunc is pure, // are teated as the same by the [Table]. A good EqualFunc is pure,
// deterministic, and fast. By default, [NewTable] uses [DefaultEqualFunc]. // deterministic, and fast. By default, [New] uses [DefaultEqualFunc].
// //
// This function MUST NOT return true if the [Hash] digest of two keys // This function MUST NOT return true if the [Hash] digest of two keys
// are different: the [Table] will not work. // are different: the [Table] will not work.

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@@ -28,7 +28,7 @@ func ExampleEqualFunc_badEqualFunc() {
// Two users with the same ID are equal. // Two users with the same ID are equal.
isEqual := func(a, b User) bool { return a.ID == b.ID } isEqual := func(a, b User) bool { return a.ID == b.ID }
userbase := cuckoo.NewCustomTable[User, bool](makeHash(1), makeHash(2), isEqual) userbase := cuckoo.NewCustom[User, bool](makeHash(1), makeHash(2), isEqual)
(userbase.Put(User{"1", "Robert Doe"}, true)) (userbase.Put(User{"1", "Robert Doe"}, true))

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@@ -1,7 +1,9 @@
package cuckoo_test package cuckoo_test
import ( import (
"fmt"
"maps" "maps"
"os"
"testing" "testing"
"github.com/stretchr/testify/assert" "github.com/stretchr/testify/assert"
@@ -25,8 +27,9 @@ type fuzzStep struct {
} }
type fuzzScenario struct { type fuzzScenario struct {
seedA, seedB uint32 seedA, seedB uint32
steps []fuzzStep capacity, growthFactor uint8
steps []fuzzStep
} }
func FuzzInsertLookup(f *testing.F) { func FuzzInsertLookup(f *testing.F) {
@@ -40,14 +43,25 @@ func FuzzInsertLookup(f *testing.F) {
return return
} }
if scenario.seedA == scenario.seedB { seedA, seedB := scenario.seedA, scenario.seedB
return growthFactor := max(2, int(scenario.growthFactor))
capacity := int(scenario.capacity)
// If they are the same number, the hashes will clash, always causing an
// error.
if seedA == seedB {
t.Skip()
} }
actual := cuckoo.NewCustomTable[uint32, uint32]( fmt.Fprintf(os.Stderr, "seedA=%d seedB=%d capacity=%d growthFactor=%d\n",
offsetHash(scenario.seedA), seedA, seedB, capacity, growthFactor)
offsetHash(scenario.seedB),
actual := cuckoo.NewCustom[uint32, uint32](
offsetHash(seedA),
offsetHash(seedB),
func(a, b uint32) bool { return a == b }, func(a, b uint32) bool { return a == b },
cuckoo.Capacity(capacity),
cuckoo.GrowthFactor(growthFactor),
) )
expected := map[uint32]uint32{} expected := map[uint32]uint32{}

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@@ -11,7 +11,7 @@ func TestMaxEvictions(t *testing.T) {
assert := assert.New(t) assert := assert.New(t)
for i := 16; i < 116; i++ { for i := 16; i < 116; i++ {
table := NewTable[int, bool](Capacity(i / 2)) table := New[int, bool](Capacity(i / 2))
expectedEvictions := 3 * math.Floor(math.Log2(float64(i))) expectedEvictions := 3 * math.Floor(math.Log2(float64(i)))
assert.Equal(table.maxEvictions(), int(expectedEvictions)) assert.Equal(table.maxEvictions(), int(expectedEvictions))
@@ -20,7 +20,7 @@ func TestMaxEvictions(t *testing.T) {
func TestLoad(t *testing.T) { func TestLoad(t *testing.T) {
assert := assert.New(t) assert := assert.New(t)
table := NewTable[int, bool](Capacity(8)) table := New[int, bool](Capacity(8))
for i := range 16 { for i := range 16 {
err := table.Put(i, true) err := table.Put(i, true)

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@@ -14,7 +14,7 @@ import (
func TestNewTable(t *testing.T) { func TestNewTable(t *testing.T) {
assert := assert.New(t) assert := assert.New(t)
table := cuckoo.NewTable[int, bool]() table := cuckoo.New[int, bool]()
assert.NotNil(table) assert.NotNil(table)
assert.Zero(table.Size()) assert.Zero(table.Size())
@@ -23,7 +23,7 @@ func TestNewTable(t *testing.T) {
func TestAddItem(t *testing.T) { func TestAddItem(t *testing.T) {
assert := assert.New(t) assert := assert.New(t)
key, value := 0, true key, value := 0, true
table := cuckoo.NewTable[int, bool]() table := cuckoo.New[int, bool]()
err := table.Put(key, value) err := table.Put(key, value)
@@ -35,7 +35,7 @@ func TestAddItem(t *testing.T) {
func TestPutOverwrite(t *testing.T) { func TestPutOverwrite(t *testing.T) {
assert := assert.New(t) assert := assert.New(t)
key, value, newValue := 0, 1, 2 key, value, newValue := 0, 1, 2
table := cuckoo.NewTable[int, int]() table := cuckoo.New[int, int]()
(table.Put(key, value)) (table.Put(key, value))
err := table.Put(key, newValue) err := table.Put(key, newValue)
@@ -50,7 +50,7 @@ func TestPutOverwrite(t *testing.T) {
func TestSameHash(t *testing.T) { func TestSameHash(t *testing.T) {
assert := assert.New(t) assert := assert.New(t)
hash := func(int) uint64 { return 0 } hash := func(int) uint64 { return 0 }
table := cuckoo.NewCustomTable[int, bool](hash, hash, cuckoo.DefaultEqualFunc[int]) table := cuckoo.NewCustom[int, bool](hash, hash, cuckoo.DefaultEqualFunc[int])
errA := table.Put(0, true) errA := table.Put(0, true)
errB := table.Put(1, true) errB := table.Put(1, true)
@@ -63,14 +63,14 @@ func TestSameHash(t *testing.T) {
func TestStartingCapacity(t *testing.T) { func TestStartingCapacity(t *testing.T) {
assert := assert.New(t) assert := assert.New(t)
table := cuckoo.NewTable[int, bool](cuckoo.Capacity(64)) table := cuckoo.New[int, bool](cuckoo.Capacity(64))
assert.Equal(uint64(128), table.TotalCapacity()) assert.Equal(uint64(128), table.TotalCapacity())
} }
func TestResizeCapacity(t *testing.T) { func TestResizeCapacity(t *testing.T) {
assert := assert.New(t) assert := assert.New(t)
table := cuckoo.NewTable[int, bool]( table := cuckoo.New[int, bool](
cuckoo.Capacity(8), cuckoo.Capacity(8),
cuckoo.GrowthFactor(2), cuckoo.GrowthFactor(2),
) )
@@ -85,7 +85,7 @@ func TestResizeCapacity(t *testing.T) {
func TestPutMany(t *testing.T) { func TestPutMany(t *testing.T) {
assert := assert.New(t) assert := assert.New(t)
expected, actual := map[int]bool{}, cuckoo.NewTable[int, bool]() expected, actual := map[int]bool{}, cuckoo.New[int, bool]()
for i := range 1_000 { for i := range 1_000 {
expected[i] = true expected[i] = true
@@ -100,7 +100,7 @@ func TestPutMany(t *testing.T) {
func TestGetMany(t *testing.T) { func TestGetMany(t *testing.T) {
assert := assert.New(t) assert := assert.New(t)
table := cuckoo.NewTable[int, bool]() table := cuckoo.New[int, bool]()
for i := range 1_000 { for i := range 1_000 {
err := table.Put(i, true) err := table.Put(i, true)
@@ -121,7 +121,7 @@ func TestGetMany(t *testing.T) {
func TestDropExistingItem(t *testing.T) { func TestDropExistingItem(t *testing.T) {
assert := assert.New(t) assert := assert.New(t)
key, value := 0, true key, value := 0, true
table := cuckoo.NewTable[int, bool]() table := cuckoo.New[int, bool]()
(table.Put(key, value)) (table.Put(key, value))
err := table.Drop(key) err := table.Drop(key)
@@ -134,7 +134,7 @@ func TestDropExistingItem(t *testing.T) {
func TestDropNoItem(t *testing.T) { func TestDropNoItem(t *testing.T) {
assert := assert.New(t) assert := assert.New(t)
key := 0 key := 0
table := cuckoo.NewTable[int, bool]() table := cuckoo.New[int, bool]()
err := table.Drop(key) err := table.Drop(key)
@@ -146,7 +146,7 @@ func TestDropNoItem(t *testing.T) {
func TestDropItemCapacity(t *testing.T) { func TestDropItemCapacity(t *testing.T) {
assert := assert.New(t) assert := assert.New(t)
key := 0 key := 0
table := cuckoo.NewTable[int, bool]( table := cuckoo.New[int, bool](
cuckoo.Capacity(64), cuckoo.Capacity(64),
cuckoo.GrowthFactor(2), cuckoo.GrowthFactor(2),
) )
@@ -164,7 +164,7 @@ func TestDropItemCapacity(t *testing.T) {
func TestPutNoCapacity(t *testing.T) { func TestPutNoCapacity(t *testing.T) {
assert := assert.New(t) assert := assert.New(t)
key, value := 0, true key, value := 0, true
table := cuckoo.NewTable[int, bool]( table := cuckoo.New[int, bool](
cuckoo.Capacity(0), cuckoo.Capacity(0),
) )
@@ -177,7 +177,7 @@ func TestPutNoCapacity(t *testing.T) {
func TestBadHashCapacity(t *testing.T) { func TestBadHashCapacity(t *testing.T) {
assert := assert.New(t) assert := assert.New(t)
table := cuckoo.NewCustomTable[int, bool]( table := cuckoo.NewCustom[int, bool](
func(int) uint64 { return 0 }, func(int) uint64 { return 0 },
func(int) uint64 { return 0 }, func(int) uint64 { return 0 },
func(a, b int) bool { return a == b }, func(a, b int) bool { return a == b },
@@ -197,7 +197,7 @@ func TestBadHashCapacity(t *testing.T) {
func TestDropResizeCapacity(t *testing.T) { func TestDropResizeCapacity(t *testing.T) {
assert := assert.New(t) assert := assert.New(t)
table := cuckoo.NewTable[int, bool]( table := cuckoo.New[int, bool](
cuckoo.Capacity(10), cuckoo.Capacity(10),
) )
@@ -217,9 +217,7 @@ func TestNewTableBy(t *testing.T) {
} }
assert := assert.New(t) assert := assert.New(t)
table := cuckoo.NewTableBy[User, bool]( table := cuckoo.NewBy[User, bool](func(u User) string { return u.id })
func(u User) string { return u.id },
)
err := table.Put(User{nil, "1", "Robert"}, true) err := table.Put(User{nil, "1", "Robert"}, true)

4
doc.go
View File

@@ -1,8 +1,8 @@
// Package cuckoo provides a hash table that uses cuckoo hashing to achieve // Package cuckoo provides a hash table that uses cuckoo hashing to achieve
// a worst-case O(1) lookup time. // a worst-case O(1) lookup time.
// //
// While a [NewTable] only supports comparable keys by default, you can create // While a [New] only supports comparable keys by default, you can create
// a table with any key type using [NewCustomTable]. Custom [Hash] functions and // a table with any key type using [NewCustom]. Custom [Hash] functions and
// key comparison are also supported. // key comparison are also supported.
// //
// See more: https://en.wikipedia.org/wiki/Cuckoo_hashing // See more: https://en.wikipedia.org/wiki/Cuckoo_hashing

View File

@@ -8,7 +8,7 @@ import (
) )
func Example_basic() { func Example_basic() {
table := cuckoo.NewTable[int, string]() table := cuckoo.New[int, string]()
if err := table.Put(1, "Hello, World!"); err != nil { if err := table.Put(1, "Hello, World!"); err != nil {
fmt.Println("Put error:", err) fmt.Println("Put error:", err)

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@@ -1,5 +1,7 @@
package cuckoo package cuckoo
import "fmt"
// DefaultCapacity is the initial capacity of a [Table]. It is inspired from // DefaultCapacity is the initial capacity of a [Table]. It is inspired from
// Java's [HashMap] implementation, which also uses 16. // Java's [HashMap] implementation, which also uses 16.
// //
@@ -7,14 +9,15 @@ package cuckoo
const DefaultCapacity uint64 = 16 const DefaultCapacity uint64 = 16
// DefaultGrowthFactor is the standard resize multiplier for a [Table]. Most // DefaultGrowthFactor is the standard resize multiplier for a [Table]. Most
// hash table implementations use 2. // implementations use 2.
const DefaultGrowthFactor uint64 = 2 const DefaultGrowthFactor uint64 = 2
// DefaultMinimumLoad is the default lowest acceptable occupancy of a [Table]. // defaultMinimumLoad is the default lowest acceptable occupancy of a [Table].
// The value of 5% is taken from [libcuckoo]. // The higher the minimum load, the more likely that a [Table.Put] will not
// succeed. The value of 5% is taken from [libcuckoo].
// //
// [libcuckoo]: https://github.com/efficient/libcuckoo/blob/656714705a055df2b7a605eb3c71586d9da1e119/libcuckoo/cuckoohash_config.hh#L21 // [libcuckoo]: https://github.com/efficient/libcuckoo/blob/656714705a055df2b7a605eb3c71586d9da1e119/libcuckoo/cuckoohash_config.hh#L21
const DefaultMinimumLoad float64 = 0.05 const defaultMinimumLoad float64 = 0.05
type settings struct { type settings struct {
growthFactor uint64 growthFactor uint64
@@ -23,23 +26,25 @@ type settings struct {
} }
// An Option modifies the settings of a [Table]. It is used in its constructors // An Option modifies the settings of a [Table]. It is used in its constructors
// like [NewTable], for example. // like [New], for example.
type Option func(*settings) type Option func(*settings)
// Capacity modifies the starting capacity of each bucket of the [Table]. The // Capacity modifies the starting capacity of each subtable of the [Table]. The
// value must be greater than 0. // value must be non-negative.
func Capacity(value int) Option { func Capacity(value int) Option {
return func(s *settings) { s.bucketSize = uint64(value) } if value < 0 {
} panic(fmt.Sprintf("go-cuckoo: Capacity must be non-negative, got %d", value))
}
// MinimumLoad modifies the [DefaultMinimumLoad] of the [Table]. The value must return func(s *settings) { s.bucketSize = uint64(value) }
// be between 0.00 and 1.00.
func MinimumLoad(value float64) Option {
return func(s *settings) { s.minLoadFactor = value }
} }
// GrowthFactor controls how much the capacity of the [Table] multiplies when // GrowthFactor controls how much the capacity of the [Table] multiplies when
// it must resize. The value must be greater than 1. // it must resize. The value must be greater than 1.
func GrowthFactor(value int) Option { func GrowthFactor(value int) Option {
if value < 2 {
panic(fmt.Sprintf("go-cuckoo: GrowthFactor must be greater than 1, got %d", value))
}
return func(s *settings) { s.growthFactor = uint64(value) } return func(s *settings) { s.growthFactor = uint64(value) }
} }

103
subtable.go Normal file
View File

@@ -0,0 +1,103 @@
package cuckoo
type entry[K, V any] struct {
key K
value V
}
type slot[K, V any] struct {
entry[K, V]
occupied bool
}
type subtable[K, V any] struct {
hash Hash[K]
slots []slot[K, V]
capacity, size uint64
compare EqualFunc[K]
}
// location determines where in the subtable a certain key would be placed. If
// the capacity is 0, this will panic.
func (t subtable[K, V]) location(key K) uint64 {
return t.hash(key) % t.capacity
}
func (t subtable[K, V]) get(key K) (value V, found bool) {
if t.capacity == 0 {
return
}
slot := t.slots[t.location(key)]
return slot.value, slot.occupied && t.compare(slot.key, key)
}
func (t *subtable[K, V]) drop(key K) (occupied bool) {
if t.capacity == 0 {
return
}
slot := &t.slots[t.location(key)]
if slot.occupied && t.compare(slot.key, key) {
slot.occupied = false
t.size--
return true
}
return false
}
func (t *subtable[K, V]) resize(capacity uint64) {
t.slots = make([]slot[K, V], capacity)
t.capacity = capacity
t.size = 0
}
func (t subtable[K, V]) update(key K, value V) (updated bool) {
if t.capacity == 0 {
return
}
slot := &t.slots[t.location(key)]
if slot.occupied && t.compare(slot.key, key) {
slot.value = value
return true
}
return false
}
func (t *subtable[K, V]) evict(insertion entry[K, V]) (evicted entry[K, V], eviction bool) {
if t.capacity == 0 {
return insertion, true
}
slot := &t.slots[t.location(insertion.key)]
if !slot.occupied {
slot.entry = insertion
slot.occupied = true
t.size++
return
}
if t.compare(slot.key, insertion.key) {
slot.value = insertion.value
return
}
insertion, slot.entry = slot.entry, insertion
return insertion, true
}
func newSubtable[K, V any](capacity uint64, hash Hash[K], compare EqualFunc[K]) subtable[K, V] {
return subtable[K, V]{
hash: hash,
capacity: capacity,
compare: compare,
size: 0,
slots: make([]slot[K, V], capacity),
}
}

103
table.go
View File

@@ -1,41 +1,50 @@
package cuckoo package cuckoo
import ( import (
"errors"
"fmt" "fmt"
"iter" "iter"
"math/bits" "math/bits"
"strings" "strings"
) )
// A Table is hash table that uses cuckoo hashing to resolve collision. Create // ErrBadHash occurs when the hashes given to a [Table] cause too many key
// one with [NewTable]. Or if you want more granularity, use [NewTableBy] or // collisions. Try rebuilding the table using:
// [NewCustomTable]. //
// 1. Different hash seeds. Equal seeds produce equal hash functions, which
// always cycle.
// 2. A different [Hash] algorithm.
var ErrBadHash = errors.New("bad hash")
// A Table which uses cuckoo hashing to resolve collision. Create
// one with [New]. Or if you want more granularity, use [NewBy] or
// [NewCustom].
type Table[K, V any] struct { type Table[K, V any] struct {
bucketA, bucketB bucket[K, V] tableA, tableB subtable[K, V]
growthFactor uint64 growthFactor uint64
minLoadFactor float64 minLoadFactor float64
} }
// TotalCapacity returns the number of slots allocated for the [Table]. To get the // TotalCapacity returns the number of slots allocated for the [Table]. To get the
// number of slots filled, look at [Table.Size]. // number of slots filled, look at [Table.Size].
func (t Table[K, V]) TotalCapacity() uint64 { func (t *Table[K, V]) TotalCapacity() uint64 {
return t.bucketA.capacity + t.bucketB.capacity return t.tableA.capacity + t.tableB.capacity
} }
// Size returns how many slots are filled in the [Table]. // Size returns how many slots are filled in the [Table].
func (t Table[K, V]) Size() int { func (t *Table[K, V]) Size() int {
return int(t.bucketA.size + t.bucketB.size) return int(t.tableA.size + t.tableB.size)
} }
func log2(n uint64) (m int) { func log2(n uint64) (m int) {
return max(0, bits.Len64(n)-1) return max(0, bits.Len64(n)-1)
} }
func (t Table[K, V]) maxEvictions() int { func (t *Table[K, V]) maxEvictions() int {
return 3 * log2(t.TotalCapacity()) return 3 * log2(t.TotalCapacity())
} }
func (t Table[K, V]) load() float64 { func (t *Table[K, V]) load() float64 {
// When there are no slots in the table, we still treat the load as 100%. // When there are no slots in the table, we still treat the load as 100%.
// Every slot in the table is full. // Every slot in the table is full.
if t.TotalCapacity() == 0 { if t.TotalCapacity() == 0 {
@@ -45,7 +54,7 @@ func (t Table[K, V]) load() float64 {
return float64(t.Size()) / float64(t.TotalCapacity()) return float64(t.Size()) / float64(t.TotalCapacity())
} }
// resize clears all buckets, changes the sizes of them to a specific capacity, // resize clears all tables, changes the sizes of them to a specific capacity,
// and fills them back up again. It is a helper function for [Table.grow] and // and fills them back up again. It is a helper function for [Table.grow] and
// [Table.shrink]; use them instead. // [Table.shrink]; use them instead.
func (t *Table[K, V]) resize(capacity uint64) error { func (t *Table[K, V]) resize(capacity uint64) error {
@@ -54,8 +63,8 @@ func (t *Table[K, V]) resize(capacity uint64) error {
entries = append(entries, entry[K, V]{k, v}) entries = append(entries, entry[K, V]{k, v})
} }
t.bucketA.resize(capacity) t.tableA.resize(capacity)
t.bucketB.resize(capacity) t.tableB.resize(capacity)
for _, entry := range entries { for _, entry := range entries {
if err := t.Put(entry.key, entry.value); err != nil { if err := t.Put(entry.key, entry.value); err != nil {
@@ -66,7 +75,7 @@ func (t *Table[K, V]) resize(capacity uint64) error {
return nil return nil
} }
// grow increases the table's capacity by the [Table.growthFactor]. If the // grow increases the table's capacity by the growth factor. If the
// capacity is 0, it increases it to 1. // capacity is 0, it increases it to 1.
func (t *Table[K, V]) grow() error { func (t *Table[K, V]) grow() error {
var newCapacity uint64 var newCapacity uint64
@@ -74,26 +83,26 @@ func (t *Table[K, V]) grow() error {
if t.TotalCapacity() == 0 { if t.TotalCapacity() == 0 {
newCapacity = 1 newCapacity = 1
} else { } else {
newCapacity = t.bucketA.capacity * t.growthFactor newCapacity = t.tableA.capacity * t.growthFactor
} }
return t.resize(newCapacity) return t.resize(newCapacity)
} }
// shrink reduces the table's capacity by the [Table.growthFactor]. It may // shrink reduces the table's capacity by the growth factor. It may
// reduce it down to 0. // reduce it down to 0.
func (t *Table[K, V]) shrink() error { func (t *Table[K, V]) shrink() error {
return t.resize(t.bucketA.capacity / t.growthFactor) return t.resize(t.tableA.capacity / t.growthFactor)
} }
// Get fetches the value for a key in the [Table]. Returns an error if no value // Get fetches the value for a key in the [Table]. Returns an error if no value
// is found. // is found.
func (t Table[K, V]) Get(key K) (value V, err error) { func (t *Table[K, V]) Get(key K) (value V, err error) {
if item, ok := t.bucketA.get(key); ok { if item, ok := t.tableA.get(key); ok {
return item, nil return item, nil
} }
if item, ok := t.bucketB.get(key); ok { if item, ok := t.tableB.get(key); ok {
return item, nil return item, nil
} }
@@ -101,34 +110,34 @@ func (t Table[K, V]) Get(key K) (value V, err error) {
} }
// Has returns true if a key has a value in the table. // Has returns true if a key has a value in the table.
func (t Table[K, V]) Has(key K) (exists bool) { func (t *Table[K, V]) Has(key K) (exists bool) {
_, err := t.Get(key) _, err := t.Get(key)
return err == nil return err == nil
} }
// Put sets the value for a key. Returns error if its value cannot be set. // Put sets the value for a key. Returns error if its value cannot be set.
func (t *Table[K, V]) Put(key K, value V) (err error) { func (t *Table[K, V]) Put(key K, value V) (err error) {
if t.bucketA.update(key, value) { if t.tableA.update(key, value) {
return nil return nil
} }
if t.bucketB.update(key, value) { if t.tableB.update(key, value) {
return nil return nil
} }
entry, eviction := entry[K, V]{key, value}, false entry, eviction := entry[K, V]{key, value}, false
for range t.maxEvictions() { for range t.maxEvictions() {
if entry, eviction = t.bucketA.evict(entry); !eviction { if entry, eviction = t.tableA.evict(entry); !eviction {
return nil return nil
} }
if entry, eviction = t.bucketB.evict(entry); !eviction { if entry, eviction = t.tableB.evict(entry); !eviction {
return nil return nil
} }
} }
if t.load() < t.minLoadFactor { if t.load() < t.minLoadFactor {
return fmt.Errorf("bad hash: resize on load %d/%d = %f", t.Size(), t.TotalCapacity(), t.load()) return fmt.Errorf("hash functions produced a cycle at load %d/%d: %w", t.Size(), t.TotalCapacity(), ErrBadHash)
} }
if err := t.grow(); err != nil { if err := t.grow(); err != nil {
@@ -141,8 +150,8 @@ func (t *Table[K, V]) Put(key K, value V) (err error) {
// Drop removes a value for a key in the table. Returns an error if its value // Drop removes a value for a key in the table. Returns an error if its value
// cannot be removed. // cannot be removed.
func (t *Table[K, V]) Drop(key K) (err error) { func (t *Table[K, V]) Drop(key K) (err error) {
t.bucketA.drop(key) t.tableA.drop(key)
t.bucketB.drop(key) t.tableB.drop(key)
if t.load() < t.minLoadFactor { if t.load() < t.minLoadFactor {
return t.shrink() return t.shrink()
@@ -152,9 +161,9 @@ func (t *Table[K, V]) Drop(key K) (err error) {
} }
// Entries returns an unordered sequence of all key-value pairs in the table. // Entries returns an unordered sequence of all key-value pairs in the table.
func (t Table[K, V]) Entries() iter.Seq2[K, V] { func (t *Table[K, V]) Entries() iter.Seq2[K, V] {
return func(yield func(K, V) bool) { return func(yield func(K, V) bool) {
for _, slot := range t.bucketA.slots { for _, slot := range t.tableA.slots {
if slot.occupied { if slot.occupied {
if !yield(slot.key, slot.value) { if !yield(slot.key, slot.value) {
return return
@@ -162,7 +171,7 @@ func (t Table[K, V]) Entries() iter.Seq2[K, V] {
} }
} }
for _, slot := range t.bucketB.slots { for _, slot := range t.tableB.slots {
if slot.occupied { if slot.occupied {
if !yield(slot.key, slot.value) { if !yield(slot.key, slot.value) {
return return
@@ -173,8 +182,8 @@ func (t Table[K, V]) Entries() iter.Seq2[K, V] {
} }
// String returns the entries of the table as a string in the format: // String returns the entries of the table as a string in the format:
// "table[k1:v1 h2:v2 ...]". // "table[k1:v1 k2:v2 ...]".
func (t Table[K, V]) String() string { func (t *Table[K, V]) String() string {
var sb strings.Builder var sb strings.Builder
sb.WriteString("table[") sb.WriteString("table[")
@@ -192,13 +201,13 @@ func (t Table[K, V]) String() string {
return sb.String() return sb.String()
} }
// NewCustomTable creates a [Table] with custom [Hash] and [EqualFunc] // NewCustom creates a [Table] with custom [Hash] and [EqualFunc]
// functions, along with any [Option] the user provides. // functions, along with any [Option] the user provides.
func NewCustomTable[K, V any](hashA, hashB Hash[K], compare EqualFunc[K], options ...Option) *Table[K, V] { func NewCustom[K, V any](hashA, hashB Hash[K], compare EqualFunc[K], options ...Option) *Table[K, V] {
settings := &settings{ settings := &settings{
growthFactor: DefaultGrowthFactor, growthFactor: DefaultGrowthFactor,
bucketSize: DefaultCapacity, bucketSize: DefaultCapacity,
minLoadFactor: DefaultMinimumLoad, minLoadFactor: defaultMinimumLoad,
} }
for _, option := range options { for _, option := range options {
@@ -208,8 +217,8 @@ func NewCustomTable[K, V any](hashA, hashB Hash[K], compare EqualFunc[K], option
return &Table[K, V]{ return &Table[K, V]{
growthFactor: settings.growthFactor, growthFactor: settings.growthFactor,
minLoadFactor: settings.minLoadFactor, minLoadFactor: settings.minLoadFactor,
bucketA: newBucket[K, V](settings.bucketSize, hashA, compare), tableA: newSubtable[K, V](settings.bucketSize, hashA, compare),
bucketB: newBucket[K, V](settings.bucketSize, hashB, compare), tableB: newSubtable[K, V](settings.bucketSize, hashB, compare),
} }
} }
@@ -217,10 +226,10 @@ func pipe[X, Y, Z any](a func(X) Y, b func(Y) Z) func(X) Z {
return func(x X) Z { return b(a(x)) } return func(x X) Z { return b(a(x)) }
} }
// NewTableBy creates a [Table] for any key type by using keyFunc to derive a // NewBy creates a [Table] for any key type by using keyFunc to derive a
// comparable key. Two keys with the same derived key are treated as equal. // comparable key. Two keys with the same derived key are treated as equal.
func NewTableBy[K, V any, C comparable](keyFunc func(K) C, options ...Option) *Table[K, V] { func NewBy[K, V any, C comparable](keyFunc func(K) C, options ...Option) *Table[K, V] {
return NewCustomTable[K, V]( return NewCustom[K, V](
pipe(keyFunc, NewDefaultHash[C]()), pipe(keyFunc, NewDefaultHash[C]()),
pipe(keyFunc, NewDefaultHash[C]()), pipe(keyFunc, NewDefaultHash[C]()),
func(a, b K) bool { return keyFunc(a) == keyFunc(b) }, func(a, b K) bool { return keyFunc(a) == keyFunc(b) },
@@ -228,10 +237,10 @@ func NewTableBy[K, V any, C comparable](keyFunc func(K) C, options ...Option) *T
) )
} }
// NewTable creates a [Table] using the default [Hash] and [EqualFunc]. Use // New creates a [Table] using the default [Hash] and [EqualFunc]. Use
// the [Option] functions to configure its behavior. Note that this constructor // the [Option] functions to configure its behavior. Note that this constructor
// is only provided for comparable keys. For arbitrary keys, consider // is only provided for comparable keys. For arbitrary keys, consider
// [NewTableBy] or [NewCustomTable]. // [NewBy] or [NewCustom].
func NewTable[K comparable, V any](options ...Option) *Table[K, V] { func New[K comparable, V any](options ...Option) *Table[K, V] {
return NewCustomTable[K, V](NewDefaultHash[K](), NewDefaultHash[K](), DefaultEqualFunc[K], options...) return NewCustom[K, V](NewDefaultHash[K](), NewDefaultHash[K](), DefaultEqualFunc[K], options...)
} }