451f4c2a8f
Before this fix quickxorhash would sometimes crash with an error like
this:
panic: runtime error: slice bounds out of range [-1248:]
This was caused by an incorrect cast of a 64 bit number to a 32 bit
one on 32 bit platforms.
See: https://forum.rclone.org/t/panic-runtime-error-slice-bounds-out-of-range/37548
137 lines
4 KiB
Go
137 lines
4 KiB
Go
// Package quickxorhash provides the quickXorHash algorithm which is a
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// quick, simple non-cryptographic hash algorithm that works by XORing
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// the bytes in a circular-shifting fashion.
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//
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// It is used by Microsoft Onedrive for Business to hash data.
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//
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// See: https://docs.microsoft.com/en-us/onedrive/developer/code-snippets/quickxorhash
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package quickxorhash
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// This code was ported from a fast C-implementation from
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// https://github.com/namazso/QuickXorHash
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// which has licenced as BSD Zero Clause License
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//
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// BSD Zero Clause License
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//
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// Copyright (c) 2022 namazso <admin@namazso.eu>
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//
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// Permission to use, copy, modify, and/or distribute this software for any
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// purpose with or without fee is hereby granted.
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//
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// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
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// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
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// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
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// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
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// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
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// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
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// PERFORMANCE OF THIS SOFTWARE.
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import "hash"
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const (
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// BlockSize is the preferred size for hashing
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BlockSize = 64
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// Size of the output checksum
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Size = 20
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shift = 11
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widthInBits = 8 * Size
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dataSize = shift * widthInBits
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)
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type quickXorHash struct {
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data [dataSize]byte
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size uint64
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}
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// New returns a new hash.Hash computing the quickXorHash checksum.
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func New() hash.Hash {
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return &quickXorHash{}
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}
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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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//
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// Write writes len(p) bytes from p to the underlying data stream. It returns
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// the number of bytes written from p (0 <= n <= len(p)) and any error
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// encountered that caused the write to stop early. Write must return a non-nil
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// error if it returns n < len(p). Write must not modify the slice data, even
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// temporarily.
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//
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// Implementations must not retain p.
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func (q *quickXorHash) Write(p []byte) (n int, err error) {
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var i int
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// fill last remain
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lastRemain := q.size % dataSize
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if lastRemain != 0 {
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i += xorBytes(q.data[lastRemain:], p)
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}
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if i != len(p) {
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for len(p)-i >= dataSize {
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i += xorBytes(q.data[:], p[i:])
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}
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xorBytes(q.data[:], p[i:])
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}
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q.size += uint64(len(p))
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return len(p), nil
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}
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// Calculate the current checksum
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func (q *quickXorHash) checkSum() (h [Size + 1]byte) {
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for i := 0; i < dataSize; i++ {
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shift := (i * 11) % 160
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shiftBytes := shift / 8
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shiftBits := shift % 8
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shifted := int(q.data[i]) << shiftBits
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h[shiftBytes] ^= byte(shifted)
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h[shiftBytes+1] ^= byte(shifted >> 8)
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}
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h[0] ^= h[20]
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// XOR the file length with the least significant bits in little endian format
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d := q.size
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h[Size-8] ^= byte(d >> (8 * 0))
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h[Size-7] ^= byte(d >> (8 * 1))
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h[Size-6] ^= byte(d >> (8 * 2))
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h[Size-5] ^= byte(d >> (8 * 3))
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h[Size-4] ^= byte(d >> (8 * 4))
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h[Size-3] ^= byte(d >> (8 * 5))
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h[Size-2] ^= byte(d >> (8 * 6))
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h[Size-1] ^= byte(d >> (8 * 7))
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return h
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}
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// Sum appends the current hash to b and returns the resulting slice.
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// It does not change the underlying hash state.
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func (q *quickXorHash) Sum(b []byte) []byte {
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hash := q.checkSum()
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return append(b, hash[:Size]...)
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}
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// Reset resets the Hash to its initial state.
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func (q *quickXorHash) Reset() {
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*q = quickXorHash{}
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}
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// Size returns the number of bytes Sum will return.
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func (q *quickXorHash) Size() int {
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return Size
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}
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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 (q *quickXorHash) BlockSize() int {
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return BlockSize
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}
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// Sum returns the quickXorHash checksum of the data.
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func Sum(data []byte) (h [Size]byte) {
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var d quickXorHash
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_, _ = d.Write(data)
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s := d.checkSum()
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copy(h[:], s[:])
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return h
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}
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