fnv.go

// Copyright (c) 2018 - 2023 Blockwatch Data Inc.
// Author: alex@blockwatch.cc

package hash

import (
	"encoding/binary"
)

// Hash64 computes the FNV-1a hash of buf.
func Hash64(buf []byte) uint64 {
	hash := uint64(offset64)
	for _, c := range buf {
		hash ^= uint64(c)
		hash *= prime64
	}
	return hash
}

// from stdlib hash/fnv/fnv.go
const (
	prime64  = 1099511628211
	offset64 = 14695981039346656037
)

// InlineFNV64a is an alloc-free port of the standard library's fnv64a.
// See https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function
type InlineFNV64a uint64

// NewInlineFNV64a returns a new instance of InlineFNV64a.
func NewInlineFNV64a() InlineFNV64a {
	return offset64
}

// Write adds data to the running hash.
func (s *InlineFNV64a) Write(data []byte) (int, error) {
	hash := uint64(*s)
	for _, c := range data {
		hash ^= uint64(c)
		hash *= prime64
	}
	*s = InlineFNV64a(hash)
	return len(data), nil
}

// Write adds data to the running hash.
func (s *InlineFNV64a) WriteString(data string) (int, error) {
	return s.Write([]byte(data))
}

// Sum64 returns the uint64 of the current resulting hash.
func (s *InlineFNV64a) Sum64() uint64 {
	return uint64(*s)
}

func (s *InlineFNV64a) Sum() []byte {
	var buf [8]byte
	binary.BigEndian.PutUint64(buf[:], s.Sum64())
	return buf[:]
}

func (s *InlineFNV64a) Reset() {
	*s = offset64
}