hash.go

// Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved

package qf

// HashFn is the signature for hash functions used
type HashFn func([]byte) uint64

// fnv64a constants
const (
	offset64 = uint64(14695981039346656037)
	prime64  = uint64(1099511628211)
)

func fnvhash(v []byte) uint64 {
	// inline fnv 64
	hv := offset64
	for _, c := range v {
		hv *= prime64
		hv ^= uint64(c)
	}
	return hv
}

// murmur mixing constants
const (
	bigM = 0xc6a4a7935bd1e995
	bigR = 47
)

func murmurhash64(v []byte) uint64 {
	var off int
	var h, k uint64

	h = uint64(len(v)) * bigM

	for l := (len(v) - off); l >= 8; l -= 8 {
		k = uint64(v[off+0]) | uint64(v[off+1])<<8 | uint64(v[off+2])<<16 | uint64(v[off+3])<<24 |
			uint64(v[off+4])<<32 | uint64(v[off+5])<<40 | uint64(v[off+6])<<48 | uint64(v[off+7])<<56

		k *= bigM
		k ^= k >> bigR
		k *= bigM

		h ^= k
		h *= bigM

		off += 8
	}

	switch len(v) - off {
	case 7:
		h ^= uint64(v[off+6]) << 48
		fallthrough
	case 6:
		h ^= uint64(v[off+5]) << 40
		fallthrough
	case 5:
		h ^= uint64(v[off+4]) << 32
		fallthrough
	case 4:
		h ^= uint64(v[off+3]) << 24
		fallthrough
	case 3:
		h ^= uint64(v[off+2]) << 16
		fallthrough
	case 2:
		h ^= uint64(v[off+1]) << 8
		fallthrough
	case 1:
		h ^= uint64(v[off+0])
		h *= bigM
	}

	h ^= h >> bigR
	h *= bigM
	h ^= h >> bigR

	return uint64(h)
}