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43 lines
1.5 KiB
Go
43 lines
1.5 KiB
Go
// Copyright 2011 The LevelDB-Go and Pebble Authors. All rights reserved. Use
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// of this source code is governed by a BSD-style license that can be found in
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// the LICENSE file.
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// Package crc implements the checksum algorithm used throughout pebble.
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//
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// The algorithm is CRC-32 with Castagnoli's polynomial, followed by a bit
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// rotation and an additional delta. The additional processing is to lessen the
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// probability of arbitrary key/value data coincidentally containing bytes that
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// look like a checksum.
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//
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// To calculate the uint32 checksum of some data:
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//
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// var u uint32 = crc.New(data).Value()
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//
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// In pebble, the uint32 value is then stored in little-endian format.
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package crc // import "github.com/cockroachdb/pebble/internal/crc"
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import "hash/crc32"
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var table = crc32.MakeTable(crc32.Castagnoli)
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// CRC is a small convenience wrapper for computing the CRC32 checksum used by
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// pebble. This is the same algorithm as used by RocksDB.
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type CRC uint32
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// New returns the result of adding the bytes to the zero-value CRC.
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func New(b []byte) CRC {
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return CRC(0).Update(b)
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}
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// Update returns the result of adding the bytes to the CRC.
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func (c CRC) Update(b []byte) CRC {
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return CRC(crc32.Update(uint32(c), table, b))
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}
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// Value returns the cooked CRC value. The additional processing is to lessen
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// the probability of arbitrary key/value data coincidentally containing bytes
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// that look like a checksum.
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func (c CRC) Value() uint32 {
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return uint32(c>>15|c<<17) + 0xa282ead8
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}
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