mirror of
https://github.com/rclone/rclone.git
synced 2024-12-23 15:38:57 +01:00
203 lines
6.1 KiB
Go
203 lines
6.1 KiB
Go
// Package quickxorhash provides the quickXorHash algorithm which is a
|
|
// quick, simple non-cryptographic hash algorithm that works by XORing
|
|
// the bytes in a circular-shifting fashion.
|
|
//
|
|
// It is used by Microsoft Onedrive for Business to hash data.
|
|
//
|
|
// See: https://docs.microsoft.com/en-us/onedrive/developer/code-snippets/quickxorhash
|
|
package quickxorhash
|
|
|
|
// This code was ported from the code snippet linked from
|
|
// https://docs.microsoft.com/en-us/onedrive/developer/code-snippets/quickxorhash
|
|
// Which has the copyright
|
|
|
|
// ------------------------------------------------------------------------------
|
|
// Copyright (c) 2016 Microsoft Corporation
|
|
//
|
|
// Permission is hereby granted, free of charge, to any person obtaining a copy
|
|
// of this software and associated documentation files (the "Software"), to deal
|
|
// in the Software without restriction, including without limitation the rights
|
|
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
|
|
// copies of the Software, and to permit persons to whom the Software is
|
|
// furnished to do so, subject to the following conditions:
|
|
//
|
|
// The above copyright notice and this permission notice shall be included in
|
|
// all copies or substantial portions of the Software.
|
|
//
|
|
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
|
|
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
|
|
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
|
|
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
|
|
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
|
|
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
|
|
// THE SOFTWARE.
|
|
// ------------------------------------------------------------------------------
|
|
|
|
import (
|
|
"hash"
|
|
)
|
|
|
|
const (
|
|
// BlockSize is the preferred size for hashing
|
|
BlockSize = 64
|
|
// Size of the output checksum
|
|
Size = 20
|
|
bitsInLastCell = 32
|
|
shift = 11
|
|
widthInBits = 8 * Size
|
|
dataSize = (widthInBits-1)/64 + 1
|
|
)
|
|
|
|
type quickXorHash struct {
|
|
data [dataSize]uint64
|
|
lengthSoFar uint64
|
|
shiftSoFar int
|
|
}
|
|
|
|
// New returns a new hash.Hash computing the quickXorHash checksum.
|
|
func New() hash.Hash {
|
|
return &quickXorHash{}
|
|
}
|
|
|
|
// Write (via the embedded io.Writer interface) adds more data to the running hash.
|
|
// It never returns an error.
|
|
//
|
|
// Write writes len(p) bytes from p to the underlying data stream. It returns
|
|
// the number of bytes written from p (0 <= n <= len(p)) and any error
|
|
// encountered that caused the write to stop early. Write must return a non-nil
|
|
// error if it returns n < len(p). Write must not modify the slice data, even
|
|
// temporarily.
|
|
//
|
|
// Implementations must not retain p.
|
|
func (q *quickXorHash) Write(p []byte) (n int, err error) {
|
|
currentshift := q.shiftSoFar
|
|
|
|
// The bitvector where we'll start xoring
|
|
vectorArrayIndex := currentshift / 64
|
|
|
|
// The position within the bit vector at which we begin xoring
|
|
vectorOffset := currentshift % 64
|
|
iterations := len(p)
|
|
if iterations > widthInBits {
|
|
iterations = widthInBits
|
|
}
|
|
|
|
for i := 0; i < iterations; i++ {
|
|
isLastCell := vectorArrayIndex == len(q.data)-1
|
|
var bitsInVectorCell int
|
|
if isLastCell {
|
|
bitsInVectorCell = bitsInLastCell
|
|
} else {
|
|
bitsInVectorCell = 64
|
|
}
|
|
|
|
// There's at least 2 bitvectors before we reach the end of the array
|
|
if vectorOffset <= bitsInVectorCell-8 {
|
|
for j := i; j < len(p); j += widthInBits {
|
|
q.data[vectorArrayIndex] ^= uint64(p[j]) << uint(vectorOffset)
|
|
}
|
|
} else {
|
|
index1 := vectorArrayIndex
|
|
var index2 int
|
|
if isLastCell {
|
|
index2 = 0
|
|
} else {
|
|
index2 = vectorArrayIndex + 1
|
|
}
|
|
low := byte(bitsInVectorCell - vectorOffset)
|
|
|
|
xoredByte := byte(0)
|
|
for j := i; j < len(p); j += widthInBits {
|
|
xoredByte ^= p[j]
|
|
}
|
|
q.data[index1] ^= uint64(xoredByte) << uint(vectorOffset)
|
|
q.data[index2] ^= uint64(xoredByte) >> low
|
|
}
|
|
vectorOffset += shift
|
|
for vectorOffset >= bitsInVectorCell {
|
|
if isLastCell {
|
|
vectorArrayIndex = 0
|
|
} else {
|
|
vectorArrayIndex = vectorArrayIndex + 1
|
|
}
|
|
vectorOffset -= bitsInVectorCell
|
|
}
|
|
}
|
|
|
|
// Update the starting position in a circular shift pattern
|
|
q.shiftSoFar = (q.shiftSoFar + shift*(len(p)%widthInBits)) % widthInBits
|
|
|
|
q.lengthSoFar += uint64(len(p))
|
|
|
|
return len(p), nil
|
|
}
|
|
|
|
// Calculate the current checksum
|
|
func (q *quickXorHash) checkSum() (h [Size]byte) {
|
|
// Output the data as little endian bytes
|
|
ph := 0
|
|
for _, d := range q.data[:len(q.data)-1] {
|
|
_ = h[ph+7] // bounds check
|
|
h[ph+0] = byte(d >> (8 * 0))
|
|
h[ph+1] = byte(d >> (8 * 1))
|
|
h[ph+2] = byte(d >> (8 * 2))
|
|
h[ph+3] = byte(d >> (8 * 3))
|
|
h[ph+4] = byte(d >> (8 * 4))
|
|
h[ph+5] = byte(d >> (8 * 5))
|
|
h[ph+6] = byte(d >> (8 * 6))
|
|
h[ph+7] = byte(d >> (8 * 7))
|
|
ph += 8
|
|
}
|
|
// remaining 32 bits
|
|
d := q.data[len(q.data)-1]
|
|
h[Size-4] = byte(d >> (8 * 0))
|
|
h[Size-3] = byte(d >> (8 * 1))
|
|
h[Size-2] = byte(d >> (8 * 2))
|
|
h[Size-1] = byte(d >> (8 * 3))
|
|
|
|
// XOR the file length with the least significant bits in little endian format
|
|
d = q.lengthSoFar
|
|
h[Size-8] ^= byte(d >> (8 * 0))
|
|
h[Size-7] ^= byte(d >> (8 * 1))
|
|
h[Size-6] ^= byte(d >> (8 * 2))
|
|
h[Size-5] ^= byte(d >> (8 * 3))
|
|
h[Size-4] ^= byte(d >> (8 * 4))
|
|
h[Size-3] ^= byte(d >> (8 * 5))
|
|
h[Size-2] ^= byte(d >> (8 * 6))
|
|
h[Size-1] ^= byte(d >> (8 * 7))
|
|
|
|
return h
|
|
}
|
|
|
|
// Sum appends the current hash to b and returns the resulting slice.
|
|
// It does not change the underlying hash state.
|
|
func (q *quickXorHash) Sum(b []byte) []byte {
|
|
hash := q.checkSum()
|
|
return append(b, hash[:]...)
|
|
}
|
|
|
|
// Reset resets the Hash to its initial state.
|
|
func (q *quickXorHash) Reset() {
|
|
*q = quickXorHash{}
|
|
}
|
|
|
|
// Size returns the number of bytes Sum will return.
|
|
func (q *quickXorHash) Size() int {
|
|
return 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 (q *quickXorHash) BlockSize() int {
|
|
return BlockSize
|
|
}
|
|
|
|
// Sum returns the quickXorHash checksum of the data.
|
|
func Sum(data []byte) [Size]byte {
|
|
var d quickXorHash
|
|
_, _ = d.Write(data)
|
|
return d.checkSum()
|
|
}
|