_CRC32
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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