xxhash.go

// Package xxhash implements the 64-bit variant of xxHash (XXH64) as described
// at http://cyan4973.github.io/xxHash/.
package xxhash

import (
	"encoding/binary"
	"errors"
	"math/bits"
)

const (
	prime1 uint64 = 11400714785074694791
	prime2 uint64 = 14029467366897019727
	prime3 uint64 = 1609587929392839161
	prime4 uint64 = 9650029242287828579
	prime5 uint64 = 2870177450012600261
)

// NOTE(caleb): I'm using both consts and vars of the primes. Using consts where
// possible in the Go code is worth a small (but measurable) performance boost
// by avoiding some MOVQs. Vars are needed for the asm and also are useful for
// convenience in the Go code in a few places where we need to intentionally
// avoid constant arithmetic (e.g., v1 := prime1 + prime2 fails because the
// result overflows a uint64).
var (
	prime1v = prime1
	prime2v = prime2
	prime3v = prime3
	prime4v = prime4
	prime5v = prime5
)

// Digest implements hash.Hash64.
type Digest struct {
	v1    uint64
	v2    uint64
	v3    uint64
	v4    uint64
	total uint64
	mem   [32]byte
	n     int // how much of mem is used
}

// New creates a new Digest that computes the 64-bit xxHash algorithm.
func New() *Digest {
	var d Digest
	d.Reset()
	return &d
}

// Reset clears the Digest's state so that it can be reused.
func (d *Digest) Reset() {
	d.v1 = prime1v + prime2
	d.v2 = prime2
	d.v3 = 0
	d.v4 = -prime1v
	d.total = 0
	d.n = 0
}

// Size always returns 8 bytes.
func (d *Digest) Size() int { return 8 }

// BlockSize always returns 32 bytes.
func (d *Digest) BlockSize() int { return 32 }

// Write adds more data to d. It always returns len(b), nil.
func (d *Digest) Write(b []byte) (n int, err error) {
	n = len(b)
	d.total += uint64(n)