// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.


// Package crc64 implements the 64-bit cyclic redundancy check, or CRC-64,
// checksum. See https://en.wikipedia.org/wiki/Cyclic_redundancy_check for
// information.
package crc64

import (
	
	
	
)

// The size of a CRC-64 checksum in bytes.
const Size = 8

// Predefined polynomials.
const (
	// The ISO polynomial, defined in ISO 3309 and used in HDLC.
	ISO = 0xD800000000000000

	// The ECMA polynomial, defined in ECMA 182.
	ECMA = 0xC96C5795D7870F42
)

// Table is a 256-word table representing the polynomial for efficient processing.
type Table [256]uint64

var (
	slicing8TablesBuildOnce sync.Once
	slicing8TableISO        *[8]Table
	slicing8TableECMA       *[8]Table
)

func buildSlicing8TablesOnce() {
	slicing8TablesBuildOnce.Do(buildSlicing8Tables)
}

func buildSlicing8Tables() {
	slicing8TableISO = makeSlicingBy8Table(makeTable(ISO))
	slicing8TableECMA = makeSlicingBy8Table(makeTable(ECMA))
}

// MakeTable returns a Table constructed from the specified polynomial.
// The contents of this Table must not be modified.
func ( uint64) *Table {
	buildSlicing8TablesOnce()
	switch  {
	case ISO:
		return &slicing8TableISO[0]
	case ECMA:
		return &slicing8TableECMA[0]
	default:
		return makeTable()
	}
}

func makeTable( uint64) *Table {
	 := new(Table)
	for  := 0;  < 256; ++ {
		 := uint64()
		for  := 0;  < 8; ++ {
			if &1 == 1 {
				 = ( >> 1) ^ 
			} else {
				 >>= 1
			}
		}
		[] = 
	}
	return 
}

func makeSlicingBy8Table( *Table) *[8]Table {
	var  [8]Table
	[0] = *
	for  := 0;  < 256; ++ {
		 := []
		for  := 1;  < 8; ++ {
			 = [&0xff] ^ ( >> 8)
			[][] = 
		}
	}
	return &
}

// digest represents the partial evaluation of a checksum.
type digest struct {
	crc uint64
	tab *Table
}

// New creates a new hash.Hash64 computing the CRC-64 checksum using the
// polynomial represented by the Table. Its Sum method will lay the
// value out in big-endian byte order. The returned Hash64 also
// implements encoding.BinaryMarshaler and encoding.BinaryUnmarshaler to
// marshal and unmarshal the internal state of the hash.
func ( *Table) hash.Hash64 { return &digest{0, } }

func ( *digest) () int { return Size }

func ( *digest) () int { return 1 }

func ( *digest) () { .crc = 0 }

const (
	magic         = "crc\x02"
	marshaledSize = len(magic) + 8 + 8
)

func ( *digest) () ([]byte, error) {
	 := make([]byte, 0, marshaledSize)
	 = append(, magic...)
	 = appendUint64(, tableSum(.tab))
	 = appendUint64(, .crc)
	return , nil
}

func ( *digest) ( []byte) error {
	if len() < len(magic) || string([:len(magic)]) != magic {
		return errors.New("hash/crc64: invalid hash state identifier")
	}
	if len() != marshaledSize {
		return errors.New("hash/crc64: invalid hash state size")
	}
	if tableSum(.tab) != readUint64([4:]) {
		return errors.New("hash/crc64: tables do not match")
	}
	.crc = readUint64([12:])
	return nil
}

func appendUint64( []byte,  uint64) []byte {
	 := [8]byte{
		byte( >> 56),
		byte( >> 48),
		byte( >> 40),
		byte( >> 32),
		byte( >> 24),
		byte( >> 16),
		byte( >> 8),
		byte(),
	}
	return append(, [:]...)
}

func readUint64( []byte) uint64 {
	_ = [7]
	return uint64([7]) | uint64([6])<<8 | uint64([5])<<16 | uint64([4])<<24 |
		uint64([3])<<32 | uint64([2])<<40 | uint64([1])<<48 | uint64([0])<<56
}

func update( uint64,  *Table,  []byte) uint64 {
	buildSlicing8TablesOnce()
	 = ^
	// Table comparison is somewhat expensive, so avoid it for small sizes
	for len() >= 64 {
		var  *[8]Table
		if * == slicing8TableECMA[0] {
			 = slicing8TableECMA
		} else if * == slicing8TableISO[0] {
			 = slicing8TableISO
			// For smaller sizes creating extended table takes too much time
		} else if len() > 16384 {
			 = makeSlicingBy8Table()
		} else {
			break
		}
		// Update using slicing-by-8
		for len() > 8 {
			 ^= uint64([0]) | uint64([1])<<8 | uint64([2])<<16 | uint64([3])<<24 |
				uint64([4])<<32 | uint64([5])<<40 | uint64([6])<<48 | uint64([7])<<56
			 = [7][&0xff] ^
				[6][(>>8)&0xff] ^
				[5][(>>16)&0xff] ^
				[4][(>>24)&0xff] ^
				[3][(>>32)&0xff] ^
				[2][(>>40)&0xff] ^
				[1][(>>48)&0xff] ^
				[0][>>56]
			 = [8:]
		}
	}
	// For reminders or small sizes
	for ,  := range  {
		 = [byte()^] ^ ( >> 8)
	}
	return ^
}

// Update returns the result of adding the bytes in p to the crc.
func ( uint64,  *Table,  []byte) uint64 {
	return update(, , )
}

func ( *digest) ( []byte) ( int,  error) {
	.crc = update(.crc, .tab, )
	return len(), nil
}

func ( *digest) () uint64 { return .crc }

func ( *digest) ( []byte) []byte {
	 := .Sum64()
	return append(, byte(>>56), byte(>>48), byte(>>40), byte(>>32), byte(>>24), byte(>>16), byte(>>8), byte())
}

// Checksum returns the CRC-64 checksum of data
// using the polynomial represented by the Table.
func ( []byte,  *Table) uint64 { return update(0, , ) }

// tableSum returns the ISO checksum of table t.
func tableSum( *Table) uint64 {
	var  [2048]byte
	 := [:0]
	if  != nil {
		for ,  := range  {
			 = appendUint64(, )
		}
	}
	return Checksum(, MakeTable(ISO))
}