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