onedrive: implement quickXorHash algorithm #2262

backend/onedrive/quickxorhash/quickxorhash.go

@@ -0,0 +1,203 @@
+// 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
+	threshold      = 600
+	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()
+}