UltraFast CrC32 needs testing!

Hi all, i needed crc32 code so i decided to use the code supplied by MrCredo in the code archives. The code is well written but very slow. Unmodified it takes on average 25-30 seconds to calculate the crc for a 20mb file. Ive added stuff to do this from memory and managed to speed it up by around 20 times but it only works for files that will fit into the remaining physical ram. Im trying to get it to do it in 10mb chuncks from memory but its proving harder than i thought. I'll post the code for people to hack :)

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Dim crc_table(255)
crc_init()


Print Hex$(crc_file("c:\test.exe"))
WaitKey

Function crc_init()
Local i
Local j
Local value
For i=0 To 255
value=i
For j=0 To 7
If (value And $1) Then
value=(value Shr 1) Xor $EDB88320
Else
value=(value Shr 1)
EndIf
Next
crc_table(i)=value
Next
End Function


Function crc_file(name$)
Local byte
Local crc
Local file
Local size
Local a
crc=$FFFFFFFF
file=ReadFile(name$)
size=FileSize("c:\test.exe")
If file=0 Then Return
bank=CreateBank(size)
ReadBytes bank,file,0,size
CloseFile file
st#=MilliSecs()
While a<>size
crc=(crc Shr 8) Xor crc_table(PeekByte(bank,a) Xor (crc And $FF))
a=a+1
Wend
et#=MilliSecs()
Print "CRC32 Checked in "+(et#-st#)/1000+" Seconds"
FreeBank bank
Return ~crc
End Function

If you look around for the blitzsys.dll it has functions to crc files or banks of data... it may be faster, but would have to time both methods :)

What is crc if you don't mind me asking? :o)

CRC

Ah, thanks man :o)

Thanx Ross i might look into later if i need the extra speed, 0.2 seconds is ok for a 20mb file for now i hope

Nice. I see you put in the 'closefile' mrcredo missed in his original code. ;)