53 lines
1.3 KiB
Go
53 lines
1.3 KiB
Go
package hyper
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import (
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"bytes"
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"encoding/gob"
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"hash/fnv"
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)
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// Decimal hashes hypercubes without collisions. For that
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// it assumes that number of buckets is 10 or less
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// and number of dimensions is 19 or less.
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func Decimal(cube []int, numBuckets int) (h uint64) {
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if numBuckets > 10 {
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panic(`Decimal hash can only be used if
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numBuckets <= 10. FNV1a can be used instead.`)
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}
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// Max uint64 equals 18446744073709551615,
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// therefore larger number of dimensions will overflow.
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if len(cube) > 19 {
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panic(`Decimal hash can only be used if
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number of dimensions is less than 20.
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FNV1a hash can be used instead.`)
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}
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for _, v := range cube {
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h = h*10 + uint64(v)
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}
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return h
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}
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// FNV1a hashes hypercubes with rare collisions,
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// and should be used when Decimal cannot be used
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// because of very large number of buckets or dimensions.
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func FNV1a(cube []int) uint64 {
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var b bytes.Buffer
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gob.NewEncoder(&b).Encode(cube)
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hash := fnv.New64a()
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hash.Write(b.Bytes())
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return hash.Sum64()
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}
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// HashFunc can be any function (also user-defined).
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type HashFunc func(hypercube []int) uint64
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// Hash64Set returns a set of hashes for a hypercube set
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// and a concrete hash function.
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func HashSet(cubeSet [][]int, hashFunc HashFunc) (
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hs []uint64) {
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for i := 0; i < len(cubeSet); i++ {
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hs = append(hs, hashFunc(cubeSet[i]))
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}
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return hs
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}
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