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Bucketed NSet
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54
README.md
54
README.md
@ -13,7 +13,7 @@ get intersections.
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- [Usage](#usage)
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- [Benchmarks](#benchmarks)
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- [How NSet works](#how-nset-works)
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- [A note on memory usage](#a-note-on-memory-usage)
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- [Memory characteristics](#memory-characteristics)
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## When to use NSet
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@ -59,8 +59,8 @@ func ExistsInArray(myArray []int, item int) bool {
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To install run `go get github.com/bloeys/nset`
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Then usage is very simple:
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```go
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```go
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mySet := nset.NewNSet[uint32]()
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mySet.Add(0)
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@ -78,24 +78,33 @@ mySet.Remove(4)
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## Benchmarks
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NSet is faster than the built-in Go hash map in all operations (add, check, delete) by `1.6x to 64x` depending on the operation and data size.
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NSet is faster than the built-in Go hash map in all operations (add, check, delete) by `~50% to ~3900%` depending on the operation and data size.
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Benchmark with 100 elements:
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In the benchmarks below, ones that have 'Rand' in the name mean that access patterns are randomized to test certain use cases.
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To make sure the test is fair the seed is the same for both Go Map and NSet. Here both suffer slowdowns but NSet remains faster.
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Adding all uint32 to the map would eat tons of RAM, so we limit both NSet and Map to 10 Million values (0->10M). But because
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NSet is optimized for this, there are two additional benchmarks that are only for NSet: `NSetRandNoSizeLimit` and `NSetContainsRandFullRange`.
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NSetAddRandNoSizeLimit removes the limit on the values so NSet will potentially get 10s or 100s of millions of random values.
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Even with no limit, NSet outperforms the Map thats limited to 10M by ~200%.
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NSetContainsRandFullRange adds all 4 billion Uint32 values to NSet then randomly checks if they exist. This is by far
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the most extreme test, but is still faster than access on a map with 400x less values. A less loaded NSet performs better,
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but the difference between best case and worst case NSet is minor and doesn't increase much as the storage increases.
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Benchmark with 100 elements (Ignore NSetContainsRandFullRange and NSetContainsRandFullRange):
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Benchmark with 10,000,000 elements:
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Benchmark with 100,000,000 elements:
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As can be seen from the benchmarks, NSet has almost no change in its performance even with 10 million elements, while the
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hash map slows down a lot as the size grows. NSet practically doesn't allocate at all. But it should be noted that
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allocation can happen when adding a number bigger than all previously entered numbers.
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As can be seen from the benchmarks, NSet has relatively small change in its performance even with 100 million elements, while the
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hash map slows down a lot as the size grows.
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Benchmarks that have 'Rand' in them mean that access patterns are randomized which can cause cache invalidation.
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To make sure the test is fair the seed is the same for both Go Map and NSet. Here both suffer slowdowns but NSet remains faster.
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Benchmarks that have `Presized` in them means that the data structure was fully allocated before usage, like:
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NSet also allocates less, and in fact will only allocate when adding a number bigger than all previously entered numbers.
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```go
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//This map already has space for ~100 elements and so doesn't need to resize, which is costly
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@ -113,10 +122,21 @@ These bit flags are stored as an array of uint64, where the `0` uses the first b
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Now assume we have added the numbers `1`, `2` and `3`, then we add number `65`. The first 3 numbers fit in the first uint64 integer of the array, but `65` doesn't
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so at this point the array is expanded until we have enough 65 bits or more, so 1 more integer is added and the second bit of the second integer is set.
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### A note on memory usage
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### Memory characteristics
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This setup gives us very high add/get/remove efficiency, but in some cases can produce worse memory usage. For example, if you make an empty set
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then add `5000` NSet will be forced to create 78 integers and then set one bit on the last integer. So if you have a few huge numbers (a number in the millions or billions) then you will be using more memory than a hash map or an array.
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then add the number `5000` NSet will be forced to create 78 integers and then set one bit on the last integer. So if you have a few huge numbers (a number in the millions or billions) then you will be using more memory than a hash map or an array.
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But if your numbers are smaller and/or closer together then you will have **a lot better** memory efficiency. An array storing all
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4 billion uint32 integers will use 16GBs of memory, while NSet with all 4 billion will only use 256MB.
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But if your numbers are smaller and/or closer together then you will have **a lot better** memory efficiency. A normal array storing all
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4 billion uint32 integers will use `16 GB` of memory, while NSet can store all 4 billion integers with only use `512 MB`.
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To improve the worst case scenario, which happens when someone just adds the number $2^{32}$ and nothing else (which uses 512 MB), NSet
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is split into 128 `buckets`, where each bucket can represent a maximum of $2^{25}$ (~33 million) values.
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The upper 7 bits of a value are used to select a bucket, then the number is placed in a position in that bucket depending on its value
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and excluding the bits used by the bucket.
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With this the worst case (e.g. adding MaxUint32) will only increase usage by **up to** `16 MB`.
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> tldr: NSet will use a max of 512 MB when storing all uint32 (as opposed to 16GB if you used an array/map), but it might reach this max before
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> adding all uint32 numbers.
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94
nset.go
94
nset.go
@ -2,14 +2,20 @@ package nset
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import (
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"fmt"
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"reflect"
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"strings"
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)
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var _ fmt.Stringer = &NSet[uint8]{}
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type BucketType uint8
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type StorageType uint64
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const StorageTypeBits = 64
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const (
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BucketCount = 128
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StorageTypeBits = 64
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BucketIndexingBits = 7
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)
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//IntsIf is limited to uint32 because we can store ALL 4 Billion uint32 numbers
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//in 256MB with NSet (instead of the normal 16GB for an array of all uint32s).
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@ -18,31 +24,43 @@ type IntsIf interface {
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uint8 | uint16 | uint32
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}
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type NSet[T IntsIf] struct {
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type Bucket struct {
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Data []StorageType
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StorageUnitCount uint64
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StorageUnitCount uint32
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}
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type NSet[T IntsIf] struct {
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Buckets [BucketCount]Bucket
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//StorageUnitCount the number of uint64 integers that are used to indicate presence of numbers in the set
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StorageUnitCount uint32
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shiftAmount T
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}
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func (n *NSet[T]) Add(x T) {
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bucket := n.GetBucketFromValue(x)
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unitIndex := n.GetStorageUnitIndex(x)
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if unitIndex >= n.Size() {
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storageUnitsToAdd := unitIndex - n.Size() + 1
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n.Data = append(n.Data, make([]StorageType, storageUnitsToAdd)...)
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if unitIndex >= bucket.StorageUnitCount {
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storageUnitsToAdd := unitIndex - bucket.StorageUnitCount + 1
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bucket.Data = append(bucket.Data, make([]StorageType, storageUnitsToAdd)...)
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n.StorageUnitCount += storageUnitsToAdd
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bucket.StorageUnitCount += storageUnitsToAdd
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}
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n.Data[unitIndex] |= 1 << (x % StorageTypeBits)
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bucket.Data[unitIndex] |= n.GetBitMask(x)
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}
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func (n *NSet[T]) Remove(x T) {
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b := n.GetBucketFromValue(x)
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unitIndex := n.GetStorageUnitIndex(x)
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if unitIndex >= n.Size() {
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if unitIndex >= b.StorageUnitCount {
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return
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}
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n.Data[unitIndex] ^= 1 << (x % StorageTypeBits)
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b.Data[unitIndex] ^= n.GetBitMask(x)
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}
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func (n *NSet[T]) Contains(x T) bool {
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@ -72,36 +90,46 @@ func (n *NSet[T]) ContainsAll(values ...T) bool {
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}
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func (n *NSet[T]) isSet(x T) bool {
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b := n.GetBucketFromValue(x)
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unitIndex := n.GetStorageUnitIndex(x)
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return unitIndex < n.Size() && n.Data[unitIndex]&(1<<(x%StorageTypeBits)) != 0
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return unitIndex < b.StorageUnitCount && b.Data[unitIndex]&n.GetBitMask(x) != 0
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}
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func (n *NSet[T]) GetStorageUnitIndex(x T) uint64 {
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return uint64(x) / StorageTypeBits
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func (n *NSet[T]) GetBucketFromValue(x T) *Bucket {
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return &n.Buckets[n.GetBucketIndex(x)]
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}
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func (n *NSet[T]) GetStorageUnit(x T) StorageType {
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return n.Data[x/StorageTypeBits]
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func (n *NSet[T]) GetBucketIndex(x T) BucketType {
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//Use the top 'n' bits as the index to the bucket
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return BucketType(x >> n.shiftAmount)
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}
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//Size returns the number of storage units
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func (n *NSet[T]) Size() uint64 {
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return n.StorageUnitCount
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func (n *NSet[T]) GetStorageUnitIndex(x T) uint32 {
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//The top 'n' bits are used to select the bucket so we need to remove them before finding storage
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//unit and bit mask. This is done by shifting left by 4 which removes the top 'n' bits,
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//then shifting right by 4 which puts the bits back to their original place, but now
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//the top 'n' bits are zeros.
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return uint32(
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((x << BucketIndexingBits) >> BucketIndexingBits) / StorageTypeBits)
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}
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func (n *NSet[T]) ElementCap() uint64 {
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return uint64(len(n.Data) * StorageTypeBits)
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func (n *NSet[T]) GetBitMask(x T) StorageType {
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//Removes top 'n' bits
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return 1 << (((x << BucketIndexingBits) >> BucketIndexingBits) % StorageTypeBits)
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}
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//String returns a string of the storage as bytes separated by spaces. A comma is between each storage unit
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func (n *NSet[T]) String() string {
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b := strings.Builder{}
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b.Grow(len(n.Data)*StorageTypeBits + len(n.Data)*2)
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b.Grow(int(n.StorageUnitCount*StorageTypeBits + n.StorageUnitCount*2))
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for i := 0; i < len(n.Data); i++ {
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for i := 0; i < len(n.Buckets); i++ {
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x := n.Data[i]
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bucket := &n.Buckets[i]
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for j := 0; j < len(bucket.Data); j++ {
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x := bucket.Data[j]
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shiftAmount := StorageTypeBits - 8
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for shiftAmount >= 0 {
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@ -116,23 +144,23 @@ func (n *NSet[T]) String() string {
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}
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b.WriteString(", ")
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}
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}
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return b.String()
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}
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func NewNSet[T IntsIf]() NSet[T] {
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func NewNSet[T IntsIf]() *NSet[T] {
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return NSet[T]{
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Data: make([]StorageType, 1),
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StorageUnitCount: 1,
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n := &NSet[T]{
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Buckets: [BucketCount]Bucket{},
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StorageUnitCount: 0,
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//We use this to either extract or clear the top 'n' bits, as they are used to select the bucket
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shiftAmount: T(reflect.TypeOf(*new(T)).Bits()) - BucketIndexingBits,
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}
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}
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//NewNSetWithMax creates a set that already has capacity to hold till at least largestNum without resizing.
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//Note that this is NOT the count of elements you want to store, instead you input the largest value you want to store. You can store larger values as well.
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func NewNSetWithMax[T IntsIf](largestNum T) NSet[T] {
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return NSet[T]{
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Data: make([]StorageType, largestNum/StorageTypeBits+1),
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StorageUnitCount: uint64(largestNum/StorageTypeBits + 1),
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for i := 0; i < len(n.Buckets); i++ {
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n.Buckets[i].Data = make([]StorageType, 0)
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}
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return n
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}
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127
nset_test.go
127
nset_test.go
@ -1,6 +1,8 @@
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package nset_test
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import (
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"fmt"
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"math"
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"math/rand"
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"testing"
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|
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@ -14,26 +16,60 @@ const (
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|
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var (
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dump int
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fullRangeNSet *nset.NSet[uint32]
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)
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func TestNSet(t *testing.T) {
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n := nset.NewNSet[uint32]()
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IsEq(t, 1, cap(n.Data))
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n.Add(0)
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n.Add(1)
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n.Add(63)
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n.Add(math.MaxUint32)
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AllTrue(t, n.Contains(0), n.Contains(1), n.Contains(63), !n.Contains(10), !n.Contains(599))
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AllTrue(t, n.Contains(0), n.Contains(1), n.Contains(63), n.Contains(math.MaxUint32), !n.Contains(10), !n.Contains(599))
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AllTrue(t, n.ContainsAll(0, 1, 63), !n.ContainsAll(9, 0, 1), !n.ContainsAll(0, 1, 63, 99))
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AllTrue(t, n.ContainsAny(0, 1, 63), n.ContainsAny(9, 99, 999, 1), !n.ContainsAny(9, 99, 999))
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IsEq(t, nset.BucketCount-1, n.GetBucketIndex(math.MaxUint32))
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IsEq(t, math.MaxUint32/64/nset.BucketCount, n.GetStorageUnitIndex(math.MaxUint32))
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|
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n.Remove(1)
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AllTrue(t, n.Contains(0), n.Contains(63), !n.Contains(1))
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}
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|
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func TestNSetFullRange(t *testing.T) {
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|
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if fullRangeNSet == nil {
|
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|
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fullRangeNSet = nset.NewNSet[uint32]()
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println("Adding all uint32 to NSet...")
|
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for i := uint32(0); i < math.MaxUint32; i++ {
|
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fullRangeNSet.Add(i)
|
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if i%1_000_000_000 == 0 {
|
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fmt.Printf("i=%d billion\n", i)
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}
|
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}
|
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fullRangeNSet.Add(math.MaxUint32)
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}
|
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|
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n := fullRangeNSet
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IsEq(t, 67_108_864, n.StorageUnitCount)
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for i := 0; i < len(n.Buckets); i++ {
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|
||||
b := &n.Buckets[i]
|
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IsEq(t, 524288, b.StorageUnitCount)
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|
||||
for j := 0; j < len(b.Data); j++ {
|
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if b.Data[j] != math.MaxUint64 {
|
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t.Errorf("Error: storage unit is NOT equal to MaxUint64 (i=%d,j=%d)! Expected math.MaxUint64 but got '%08b'\n",
|
||||
i,
|
||||
j,
|
||||
b.Data[j])
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
n = nset.NewNSetWithMax[uint32](100)
|
||||
IsEq(t, 2, cap(n.Data))
|
||||
}
|
||||
|
||||
func AllTrue(t *testing.T, values ...bool) bool {
|
||||
@ -85,6 +121,16 @@ func BenchmarkNSetAddRand(b *testing.B) {
|
||||
}
|
||||
}
|
||||
|
||||
func BenchmarkNSetAddRandNoSizeLimit(b *testing.B) {
|
||||
|
||||
n := nset.NewNSet[uint32]()
|
||||
|
||||
rand.Seed(RandSeed)
|
||||
for i := 0; i < b.N; i++ {
|
||||
n.Add(rand.Uint32())
|
||||
}
|
||||
}
|
||||
|
||||
func BenchmarkMapAddRand(b *testing.B) {
|
||||
|
||||
hMap := map[uint32]struct{}{}
|
||||
@ -95,44 +141,6 @@ func BenchmarkMapAddRand(b *testing.B) {
|
||||
}
|
||||
}
|
||||
|
||||
func BenchmarkNSetAddPresized(b *testing.B) {
|
||||
|
||||
n := nset.NewNSetWithMax[uint32](maxBenchSize - 1)
|
||||
|
||||
for i := uint32(0); i < uint32(b.N); i++ {
|
||||
n.Add(i % maxBenchSize)
|
||||
}
|
||||
}
|
||||
|
||||
func BenchmarkMapAddPresized(b *testing.B) {
|
||||
|
||||
hMap := make(map[uint32]struct{}, maxBenchSize-1)
|
||||
|
||||
for i := uint32(0); i < uint32(b.N); i++ {
|
||||
hMap[i%maxBenchSize] = struct{}{}
|
||||
}
|
||||
}
|
||||
|
||||
func BenchmarkNSetAddPresizedRand(b *testing.B) {
|
||||
|
||||
n := nset.NewNSetWithMax[uint32](maxBenchSize - 1)
|
||||
|
||||
rand.Seed(RandSeed)
|
||||
for i := 0; i < b.N; i++ {
|
||||
n.Add(rand.Uint32() % maxBenchSize)
|
||||
}
|
||||
}
|
||||
|
||||
func BenchmarkMapAddPresizedRand(b *testing.B) {
|
||||
|
||||
hMap := make(map[uint32]struct{}, maxBenchSize-1)
|
||||
|
||||
rand.Seed(RandSeed)
|
||||
for i := 0; i < b.N; i++ {
|
||||
hMap[rand.Uint32()%maxBenchSize] = struct{}{}
|
||||
}
|
||||
}
|
||||
|
||||
func BenchmarkNSetContains(b *testing.B) {
|
||||
|
||||
//Init
|
||||
@ -202,6 +210,39 @@ func BenchmarkNSetContainsRand(b *testing.B) {
|
||||
dump = found
|
||||
}
|
||||
|
||||
func BenchmarkNSetContainsRandFullRange(b *testing.B) {
|
||||
|
||||
//Init
|
||||
if fullRangeNSet == nil {
|
||||
|
||||
b.StopTimer()
|
||||
|
||||
fullRangeNSet = nset.NewNSet[uint32]()
|
||||
println("Preparing full range NSet...")
|
||||
for i := uint32(0); i < math.MaxUint32; i++ {
|
||||
fullRangeNSet.Add(i)
|
||||
}
|
||||
fullRangeNSet.Add(math.MaxUint32)
|
||||
|
||||
b.StartTimer()
|
||||
}
|
||||
|
||||
n := fullRangeNSet
|
||||
|
||||
//Work
|
||||
found := 0
|
||||
rand.Seed(RandSeed)
|
||||
for i := 0; i < b.N; i++ {
|
||||
|
||||
randVal := rand.Uint32()
|
||||
if n.Contains(randVal) {
|
||||
found++
|
||||
}
|
||||
}
|
||||
|
||||
dump = found
|
||||
}
|
||||
|
||||
func BenchmarkMapContainsRand(b *testing.B) {
|
||||
|
||||
//Init
|
||||
|
||||
Reference in New Issue
Block a user