piotrkowalczuk/mnemosyne

package jump

import (
    "hash"
    "hash/crc64"
    "io"
    "sync"
)

var hasher = sync.Pool{
    New: func() interface{} {
        return crc64.New(crc64.MakeTable(crc64.ECMA))
    },
}

// Hash consistently chooses a hash bucket number in the range [0, numBuckets) for the given key.
// numBuckets must be >= 1.
func Hash(key uint64, numBuckets int) int32 {
    var b int64 = -1
    var j int64

    for j < int64(numBuckets) {
        b = j
        key = key*2862933555777941757 + 1
        j = int64(float64(b+1) * (float64(int64(1)<<31) / float64((key>>33)+1)))
    }

    return int32(b)
}

// HashString works like hash but accept string as an input.
func HashString(key string, numBuckets int) int32 {
    // jump.Hash returns values from 0.
    k := Hash(Sum64(key), numBuckets)

    return k
}

// Sum64 ...
func Sum64(key string) uint64 {
    h := hasher.Get().(hash.Hash64)
    if _, err := io.WriteString(h, key); err != nil {
        panic(err)
    }
    r := h.Sum64()
    h.Reset()
    hasher.Put(h)
    return r
}