Class: CRCStream

• Inheritance
• Description
• Class protocol
  • initialization
  • instance creation
• Instance protocol
  • accessing
  • initialization
  • queries
  • writing

Inheritance:

   Object
   |
   +--Stream
      |
      +--HashStream
         |
         +--CRCStream
            |
            +--CRC16Stream
            |
            +--CRC32Stream
            |
            +--CRC8Stream

Package:

stx:libbasic2

Category:

System-Crypt-Hashing

Version:

rev: 1.13 date: 2019/06/06 21:17:07

user: cg

file: CRCStream.st directory: libbasic2

module: stx stc-classLibrary: libbasic2

Description:

abstract superclass of crc streams;
refactored from original crc32 stream.
For details, see https://en.wikipedia.org/wiki/Cyclic_redundancy_check

Only use CRC to protect against communication errors;
DO NOT use CRC for cryptography, authentication, security, etc.
- use secure hashes for those instead.

[parameters:] 
    polynomials:
        CRC_POLY_16             0xA001
        CRC_POLY_32             0xEDB88320L
        CRC_POLY_CCITT          0x1021
        CRC_POLY_DNP            0xA6BC
        CRC_POLY_KERMIT         0x8408

    start values:
        CRC_START_8             0x00
        CRC_START_16            0x0000
        CRC_START_MODBUS        0xFFFF
        CRC_START_XMODEM        0x0000
        CRC_START_CCITT_1D0F    0x1D0F
        CRC_START_CCITT_FFFF    0xFFFF
        CRC_START_KERMIT        0x0000
        CRC_START_SICK          0x0000
        CRC_START_DNP           0x0000
        CRC_START_32            0xFFFFFFFF

Class protocol:

 crcTableFor: generatorPolynomInteger

construct the polynom-specific lookup table

usage example(s):

CRC8Stream crcTableFor:(16r1D bitReversed8)

 flushCrcTables

CRC16Stream flushCrcTables
CRC32Stream flushCrcTables

 generatorPolynom: anLSBInteger

notice, in literature, the generator polynom is usually specified as an MSB number

usage example(s):

self assert:((self generatorPolynom:16r82F63B78) nextPut:'123456789'; hashValue) = 16rE3069283

 generatorPolynom: anLSBInteger initValue: initValue

notice, in literature, the generator polynom is usually specified as an MSB number

usage example(s):

self assert:((self generatorPolynom:16r82F63B78) nextPut:'123456789'; hashValue) = 16rE3069283

 generatorPolynom: anLSBInteger initValue: initValue xorOut: xorOut

notice, in literature, the generator polynom is usually specified as an MSB number

usage example(s):

self assert:((self generatorPolynom:16r82F63B78) nextPut:'123456789'; hashValue) = 16rE3069283

Instance protocol:

 generatorPolynom

answer the generator polynom (LSB)

 initValue

answer the init value

 xorOut

answer the xorOut value

 generatorPolynom: polyLSB initValue: initValueArg xorOut: xorOutArg

set the generator polynom for this instance.
And set start and xorOut.
Computes the crcTable for this polynom.
Notice the bit order is LSB

 reset

reset the current crc value

 hashValue

return the computed CRC

 nextPutBytes: count from: anObject startingAt: start

add the hash of anObject to the computed hash so far.