

Task

Demonstrate a method of deriving the Cyclic Redundancy Check from within the language.



The result should be in accordance with ISO 3309, ITU-T V.42, Gzip and PNG.

Algorithms are described on Computation of CRC in Wikipedia.
This variant of CRC-32 uses LSB-first order, sets the initial CRC to FFFFFFFF16, and complements the final CRC.

For the purpose of this task, generate a CRC-32 checksum for the ASCII encoded string:

 The quick brown fox jumps over the lazy dog


CRC32(str, enc = "UTF-8")
{
    l := (enc = "CP1200" || enc = "UTF-16") ? 2 : 1, s := (StrPut(str, enc) - 1) * l
    VarSetCapacity(b, s, 0) && StrPut(str, &b, floor(s / l), enc)
    CRC32 := DllCall("ntdll.dll\RtlComputeCrc32", "UInt", 0, "Ptr", &b, "UInt", s)
    return Format("{:#x}", CRC32)
}
 
MsgBox % CRC32("The quick brown fox jumps over the lazy dog")