CRC32

The _CRC32 function returns the Crc-32 checksum of any arbitrary string.

Syntax

chksum~& = _CRC32(dataString$)

Parameters

• chksum~& is the _UNSIGNED LONG checksum returned (zero (0), if the given dataString$ was empty).
• dataString$ is any literal or variable STRING to build the checksum from.

Description

• The Crc-32 checksum algorithm is slower than _ADLER32 but is usually more resistant against random collisions, it has the following known properties:
  • All single bit flips will be detected.
  • All double bit flips will be detected.
  • All 32-bit bursts of errors will be detected.
  • Has a hamming distance of 4 for data lengths up to 91706 bytes.
  • Has a hamming distance of 5 for data lengths up to 2974 bytes.
• For more informations have a closer look at Chapters 5-7 here.

Availability

• 

  none

• 

  v3.12.0

• 
• 

  yes

• 

  yes

• 

  yes

Examples

Example

Showing how the Crc-32 checksum can detect differences in two strings.

'this is the correct text t$ = "QB64 Phoenix Edition" PRINT "Correct Text: "; t$ PRINT " Crc-32 Sum: "; RIGHT$("00000000" + HEX$(_CRC32(t$)), 8) PRINT 'this text differs in just 1 bit from the above, by changing 4 to 5 'ASC("4") = 52 = &B00110100 'ASC("5") = 53 = &B00110101 t$ = "QB65 Phoenix Edition" PRINT "Mangled Text: "; t$ PRINT " Crc-32 Sum: "; RIGHT$("00000000" + HEX$(_CRC32(t$)), 8) END

Correct Text: QB64 Phoenix Edition Crc-32 Sum: 691EE005 Mangled Text: QB65 Phoenix Edition Crc-32 Sum: EEB82B46

See also

• _DEFLATE$, _INFLATE$
• _ADLER32, _MD5$

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