Class: CRC32Stream

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

Inheritance:

   Object
   |
   +--Stream
      |
      +--HashStream
         |
         +--CRC32Stream

Package:

stx:libbasic2

Category:

System-Crypt-Hashing

Version:

rev: 1.28 date: 2016/12/20 21:39:17

user: cg

file: CRC32Stream.st directory: libbasic2

module: stx stc-classLibrary: libbasic2

Author:

Stefan Vogel (stefan@zwerg)

Description:

Standard CRC method as defined by ISO 3309 [ISO-3309] or ITU-T V.42 [ITU-T-V42].
The default CRC polynomial employed is

    x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x+1
    (or 16r04C11DB7)

You can also create an instace performing the Castagnioli CRC-32C
(used in iSCSI & SCTP, G.hn payload, SSE4.2):

    self newCrc32c

    x32 + x28 + x27 + x26 + x25 + x23 + x22 + x20 + x19 + x18 + x14 + x13 + x11 + x10 + x9 + x8 + x6 + 1

Only use CRC to protect against communication errors;
do NOT use CRC for cryptography - use SHA1Stream or MD5Stream instead.

Notice that this CRC is also used with PNG images - therefore, its performance
directly affects png image processing.

throughput:
    220 Mb/s on MacBook Pro (2.6Ghz I7)
    157000 Kb/s on a 2.5Ghz 64X2 Athlon 4800+ (64bit)
    150000 Kb/s on 2Ghz Duo


[instance variables:]

[class variables:]

Related information:

    SHA1Stream
    MD5Stream

Class protocol:

 crcTableFor: generatorPolynomInteger

 initialize

 generatorPolynom: anInteger

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

 newCrc32c

return an instance of the Castagnoli CRC-32
x32 + x28 + x27 + x26 + x25 + x23 + x22 + x20 + x19 + x18 + x14 + x13 + x11 + x10 + x9 + x8 + x6 + 1
(used in iSCSI & SCTP, G.hn payload, SSE4.2)

usage example(s):

Castagnoli crc: self assert:((self newCrc32c) nextPut:'123456789'; hashValue) = 3808858755. '16rE3069283' default crc: self assert:((self new) nextPut:'123456789'; hashValue) = 3421780262. '16rCBF43926'

Instance protocol:

 generatorPolynom

answer the generator polynom

 generatorPolynom: anInteger

set the generator polynom for this instance.
Note: you have to set the bit-reversed value, so the LSB must be first

 reset

reset the current crc value

 initialize

initialize the CRC to CRC-32 ITU-T:
x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x+1

 hashValue

return the computed CRC

 nextPutBytes: count from: anObject startingAt: start

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

Examples:

  self information:(CRC32Stream hashValueOf:'resume') hexPrintString

  self information:(CRC32Stream new
                          nextPut:$r;
                          nextPut:$e;
                          nextPut:$s;
                          nextPut:$u;
                          nextPut:$m;
                          nextPut:$e;
                          hashValue) hexPrintString

  self information:(CRC32Stream hashValueOf:#[1 2 3 4 5 6 7]) hexPrintString

  self information:((CRC32Stream hashValueOf:#[16rFF 16rFF 16rFF 16rFF 16rFF 16rFF 16rFF 16rFF 16rFF 16rFF
           16rFF 16rFF 16rFF 16rFF 16rFF 16rFF 16rFF 16rFF 16rFF 16rFF
           16rFF 16rFF 16rFF 16rFF 16rFF 16rFF 16rFF 16rFF 16rFF 16rFF
           16rFF 16rFF 16rFF 16rFF 16rFF 16rFF 16rFF 16rFF 16rFF 16rFF]) hexPrintString)

  |hashStream n t|

  hashStream := CRC32Stream new.
  n := 1000000.
  t := Time millisecondsToRun:[
          n timesRepeat:[
              hashStream nextPutAll:'12345678901234567890123456789012345678901234567890'.
          ].
       ].
  t := (t / 1000) asFloat.
  Transcript show:'crc32:'; showCR: hashStream hashValue hexPrintString.
  Transcript show:t; show:' seconds for '; show:(50*n/1024) asFloat; showCR:' Kb'.
  Transcript show:(n*50/1024 / t); showCR:' Kb/s'