crc-32

[blametroi]

I wanted to create a hash on a file and figured I'd use a CRC. After some research I was beginning to think I should be using another language for what I was doing (bit shifts), but then I found out there's a CRC-32 API call in windows. Stealing the idea from rosettacode, here's a LB example of calculating a CRC-32 on a string in case anyone is interested.



' crc32.bas - attempt to use the rtlComputeCrc32 function from nt.dll
' on windows.
'

' borrowing from the vb example on https://rosettacode.org/wiki/CRC-32


' In ntdll.dll we have:
'
' RtlComputeCrc32( byval initial as Long, pdata as Any, byval ilen as long) as long
'
' crc32 of "The quick brown fox jumps over the lazy dog" should be
' &H414FA339, is it?

s$ = "The quick brown fox jumps over the lazy dog"
ls = len(s$)

print "calculating crc-32 of : "; s$
print "expected crc-32 is    : "; dechex$(hexdec("&H414FA339"))

open "ntdll.dll" for dll as #ntdll
calldll #ntdll, "RtlComputeCrc32", 0 as long, s$ as ptr, ls as long, result as long
close #ntdll

print "calculated crc-32 is  : "; dechex$(result)

if result = hexdec("&H414FA339") then
   print "crc-32 calculated correctly"
else
   print "crc-32 calculated is incorrect!"
end if

print
print "done"