github.com/zuoyebang/bitalostable@v1.0.1-0.20240229032404-e3b99a834294/internal/crc/crc.go (about)

     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 bitalostable.
     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 bitalostable, the uint32 value is then stored in little-endian format.
    17  package crc // import "github.com/zuoyebang/bitalostable/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  // bitalostable. 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  func New(b []byte) CRC {
    29  	return CRC(0).Update(b)
    30  }
    31  
    32  // Update returns the result of adding the bytes to the CRC.
    33  func (c CRC) Update(b []byte) CRC {
    34  	return CRC(crc32.Update(uint32(c), table, b))
    35  }
    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  func (c CRC) Value() uint32 {
    41  	return uint32(c>>15|c<<17) + 0xa282ead8
    42  }