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1 : // Copyright 2011 The LevelDB-Go and Pebble Authors. All rights reserved. Use 2 : // of this source code is governed by a BSD-style license that can be found in 3 : // the LICENSE file. 4 : 5 : // Package crc implements the checksum algorithm used throughout pebble. 6 : // 7 : // The algorithm is CRC-32 with Castagnoli's polynomial, followed by a bit 8 : // rotation and an additional delta. The additional processing is to lessen the 9 : // probability of arbitrary key/value data coincidentally containing bytes that 10 : // look like a checksum. 11 : // 12 : // To calculate the uint32 checksum of some data: 13 : // 14 : // var u uint32 = crc.New(data).Value() 15 : // 16 : // In pebble, the uint32 value is then stored in little-endian format. 17 : package crc // import "github.com/cockroachdb/pebble/internal/crc" 18 : 19 : import "hash/crc32" 20 : 21 : var table = crc32.MakeTable(crc32.Castagnoli) 22 : 23 : // CRC is a small convenience wrapper for computing the CRC32 checksum used by 24 : // pebble. This is the same algorithm as used by RocksDB. 25 : type CRC uint32 26 : 27 : // New returns the result of adding the bytes to the zero-value CRC. 28 2 : func New(b []byte) CRC { 29 2 : return CRC(0).Update(b) 30 2 : } 31 : 32 : // Update returns the result of adding the bytes to the CRC. 33 2 : func (c CRC) Update(b []byte) CRC { 34 2 : return CRC(crc32.Update(uint32(c), table, b)) 35 2 : } 36 : 37 : // Value returns the cooked CRC value. The additional processing is to lessen 38 : // the probability of arbitrary key/value data coincidentally containing bytes 39 : // that look like a checksum. 40 2 : func (c CRC) Value() uint32 { 41 2 : return uint32(c>>15|c<<17) + 0xa282ead8 42 2 : }