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95 lines
2.6 KiB
Go
95 lines
2.6 KiB
Go
package jump
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import (
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"hash"
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"hash/crc32"
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"hash/crc64"
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"hash/fnv"
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"io"
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)
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// Hash takes a 64 bit key and the number of buckets. It outputs a bucket
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// number in the range [0, buckets).
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// If the number of buckets is less than or equal to 0 then one 1 is used.
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func Hash(key uint64, buckets int32) int32 {
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var b, j int64
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if buckets <= 0 {
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buckets = 1
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}
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for j < int64(buckets) {
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b = j
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key = key*2862933555777941757 + 1
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j = int64(float64(b+1) * (float64(int64(1)<<31) / float64((key>>33)+1)))
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}
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return int32(b)
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}
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// HashString takes string as key instead of an int and uses a KeyHasher to
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// generate a key compatible with Hash().
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func HashString(key string, buckets int32, h KeyHasher) int32 {
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h.Reset()
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_, err := io.WriteString(h, key)
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if err != nil {
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panic(err)
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}
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return Hash(h.Sum64(), buckets)
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}
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// KeyHasher is a subset of hash.Hash64 in the standard library.
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type KeyHasher interface {
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// Write (via the embedded io.Writer interface) adds more data to the
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// running hash.
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// It never returns an error.
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io.Writer
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// Reset resets the KeyHasher to its initial state.
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Reset()
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// Return the result of the added bytes (via io.Writer).
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Sum64() uint64
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}
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// Hasher represents a jump consistent hasher using a string as key.
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type Hasher struct {
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n int32
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h KeyHasher
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}
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// New returns a new instance of of Hasher.
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func New(n int, h KeyHasher) *Hasher {
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return &Hasher{int32(n), h}
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}
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// N returns the number of buckets the hasher can assign to.
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func (h *Hasher) N() int {
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return int(h.n)
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}
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// Hash returns the integer hash for the given key.
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func (h *Hasher) Hash(key string) int {
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return int(HashString(key, h.n, h.h))
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}
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// KeyHashers available in the standard library for use with HashString() and Hasher.
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var (
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// CRC32 uses the 32-bit Cyclic Redundancy Check (CRC-32) with the IEEE
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// polynomial.
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NewCRC32 func() hash.Hash64 = func() hash.Hash64 { return &crc32Hasher{crc32.NewIEEE()} }
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// CRC64 uses the 64-bit Cyclic Redundancy Check (CRC-64) with the ECMA
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// polynomial.
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NewCRC64 func() hash.Hash64 = func() hash.Hash64 { return crc64.New(crc64.MakeTable(crc64.ECMA)) }
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// FNV1 uses the non-cryptographic hash function FNV-1.
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NewFNV1 func() hash.Hash64 = func() hash.Hash64 { return fnv.New64() }
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// FNV1a uses the non-cryptographic hash function FNV-1a.
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NewFNV1a func() hash.Hash64 = func() hash.Hash64 { return fnv.New64a() }
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// These are deprecated because they're not safe for concurrent use. Please
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// use the New* functions instead.
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CRC32 hash.Hash64 = &crc32Hasher{crc32.NewIEEE()}
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CRC64 hash.Hash64 = crc64.New(crc64.MakeTable(crc64.ECMA))
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FNV1 hash.Hash64 = fnv.New64()
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FNV1a hash.Hash64 = fnv.New64a()
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)
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