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package oss
import (
"hash"
"hash/crc64"
)
// digest represents the partial evaluation of a checksum.
type digest struct {
crc uint64
tab *crc64.Table
}
// NewCRC creates a new hash.Hash64 computing the CRC-64 checksum
// using the polynomial represented by the Table.
func NewCRC(tab *crc64.Table, init uint64) hash.Hash64 { return &digest{init, tab} }
// Size returns the number of bytes Sum will return.
func (d *digest) Size() int { return crc64.Size }
// BlockSize returns the hash's underlying block size.
// The Write method must be able to accept any amount
// of data, but it may operate more efficiently if all writes
// are a multiple of the block size.
func (d *digest) BlockSize() int { return 1 }
// Reset resets the Hash to its initial state.
func (d *digest) Reset() { d.crc = 0 }
// Write (via the embedded io.Writer interface) adds more data to the running hash.
// It never returns an error.
func (d *digest) Write(p []byte) (n int, err error) {
d.crc = crc64.Update(d.crc, d.tab, p)
return len(p), nil
}
// Sum64 returns crc64 value.
func (d *digest) Sum64() uint64 { return d.crc }
// Sum returns hash value.
func (d *digest) Sum(in []byte) []byte {
s := d.Sum64()
return append(in, byte(s>>56), byte(s>>48), byte(s>>40), byte(s>>32), byte(s>>24), byte(s>>16), byte(s>>8), byte(s))
}
// gf2Dim dimension of GF(2) vectors (length of CRC)
const gf2Dim int = 64
func gf2MatrixTimes(mat []uint64, vec uint64) uint64 {
var sum uint64
for i := 0; vec != 0; i++ {
if vec&1 != 0 {
sum ^= mat[i]
}
vec >>= 1
}
return sum
}
func gf2MatrixSquare(square []uint64, mat []uint64) {
for n := 0; n < gf2Dim; n++ {
square[n] = gf2MatrixTimes(mat, mat[n])
}
}
// CRC64Combine combine crc64
func CRC64Combine(crc1 uint64, crc2 uint64, len2 uint64) uint64 {
var even [gf2Dim]uint64 // even-power-of-two zeros operator
var odd [gf2Dim]uint64 // odd-power-of-two zeros operator
// Degenerate case
if len2 == 0 {
return crc1
}
// Put operator for one zero bit in odd
odd[0] = crc64.ECMA // CRC64 polynomial
var row uint64 = 1
for n := 1; n < gf2Dim; n++ {
odd[n] = row
row <<= 1
}
// Put operator for two zero bits in even
gf2MatrixSquare(even[:], odd[:])
// Put operator for four zero bits in odd
gf2MatrixSquare(odd[:], even[:])
// Apply len2 zeros to crc1, first square will put the operator for one zero byte, eight zero bits, in even
for {
// Apply zeros operator for this bit of len2
gf2MatrixSquare(even[:], odd[:])
if len2&1 != 0 {
crc1 = gf2MatrixTimes(even[:], crc1)
}
len2 >>= 1
// If no more bits set, then done
if len2 == 0 {
break
}
// Another iteration of the loop with odd and even swapped
gf2MatrixSquare(odd[:], even[:])
if len2&1 != 0 {
crc1 = gf2MatrixTimes(odd[:], crc1)
}
len2 >>= 1
// If no more bits set, then done
if len2 == 0 {
break
}
}
// Return combined crc
crc1 ^= crc2
return crc1
}