CRC32 check with bmx?

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Grisu (Posted 2005) [#1]

Hi! Has someone written funcs in bmx that check if the checksum of a file is correct? They need not be über fast, so plain stuff would do fine. I looked up the archives but couldn't port the code there over to bmx.

Yan (Posted 2005) [#2]

The code from the archive seems to need little modification?? Global crc_table[256] crc_init() Print Hex$(crc_string("ABC")) End Function crc_init() Local i Local j Local value For i=0 To 255 value=i For j=0 To 7 If (value & $1) Then value=(value Shr 1) ~ $EDB88320 Else value=(value Shr 1) EndIf Next crc_table[i]=value Next End Function Function crc_string(txt$) Local bbyte Local crc Local i Local size crc=$FFFFFFFF size=Len(txt$) For i=1 To size bbyte=Asc(Mid$(txt$,i,1)) crc=(crc Shr 8) ~ crc_table[bbyte ~ (crc & $FF)] Next Return ~crc End Function Function crc_bank(bank) Local bbyte Local crc Local i Local size crc=$FFFFFFFF size=BankSize(bank)-1 For i=0 To size bbyte=PeekByte(bank,i) crc=(crc Shr 8) ~ crc_table[bbyte ~ (crc & $FF)] Next Return ~crc End Function Function crc_file(name$) Local bbyte Local crc Local file:TStream crc=$FFFFFFFF file=ReadFile(name$) If file=Null Then Return While Not Eof(file) bbyte=ReadByte(file) crc=(crc Shr 8) ~ crc_table[bbyte ~ (crc & $FF)] Wend CloseFile file Return ~crc End Function NOTE: I've only changed things enough to get it running, I haven't fully maxerised the code.

Grisu (Posted 2005) [#3]

At least it works now. Thanks! Its just aweful slow when you "test" some bigger files. Might be the readbyte command.

Grisu (Posted 2005) [#4]

Function crc_file(name$) Local crc,size,i size=FileSize(name$) Local bbyte:Byte[size] crc=$FFFFFFFF bbyte=LoadByteArray(name$) For i=0 To size crc=(crc Shr 8) ~ crc_table[bbyte[i] ~ (crc & $FF)] Next bbyte=Null FlushMem() Return ~crc End Function Done a speed up for file checking!