Re^2: Test binary equality?

    my @SB;
    my $Temp;
    sysopen(DEV, $Device, O_RDWR | O_SYNC) || die("Error: $!\n");
    
    sysseek(DEV,0,0) || die("$!\n");
    sysread(DEV,$SB[0],512) || die("1 $!\n");
    sysseek(DEV,0,0) || die("$!\n");
    sysread(DEV,$SB[1],512) || die("2 $!\n");
    sysseek(DEV,-1024,2) || die("$!\n");
    sysread(DEV,$SB[2],512) || die("3 $!\n");
    sysseek(DEV,-512,2) || die("$!\n");
    sysread(DEV,$SB[3],512) || die("4 $!\n");
    
    if (!($SB[0] eq $SB[1]))
    {
        my @Pair;
        warn("Error, First 2 superblocks do not match! Checking third.
+..");
        foreach my $I (0 .. 1)
        {
            @Pair = ($I,2) if ($SB[$I] eq $SB[2]);
        }
        if (!((@Pair[0]) && (@Pair[1])))
        {
            warn("Error, First 3 superblocks do not match! Checking fo
+urth and final...");
            foreach my $I (0 .. 2)
            {
                @Pair = ($I,3) if ($SB[$I] eq $SB[3]);
            }
            if (!((@Pair[0]) && (@Pair[1])))
            {
                die("All 4 superblock copies are different! This is ma
+jior corruption.\n");
            }
        }
        $SB[0] = $Pair[1];
    }
[download]

I know that they are not equal though, here are the first 1024 bytes:

Abydos OEFS # hexdump -C -n 1024 /dev/sdf1
00000000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |.........
+.......|
*
00000200  4f 45 46 53 2d 30 30 30  30 2e 30 30 30 30 30 30  |OEFS-0000
+.000000|
00000210  f0 26 3f f0 9d 1f dc 11  93 c2 d9 64 65 f2 e8 c0  |.&?......
+..de...|
00000220  53 74 72 75 01 00 00 00  00 00 00 00 00 00 00 00  |Stru.....
+.......|
00000230  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |.........
+.......|
*
00000400
[download]

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Re^3: Test binary equality? by ysth (Canon) on Jun 21, 2007 at 03:15 UTC
Your first two seeks are to the same position. !(... eq ...) is usually written ... ne ...	[reply]
Re^4: Test binary equality? by exodist (Monk) on Jun 21, 2007 at 03:18 UTC
Thank you, I noticed that just after posting :-( as for the eq thing, oops, I missed that (I first tested equality, then negated it.)	[reply]
Re^3: Test binary equality? by graff (Chancellor) on Jun 21, 2007 at 03:30 UTC
At the top of this thread, you said: All for places in the file should be exact copies of eachother, as in all 4 elements of the array should now contain the same exact binary data. (You meant "all four places", right?) But your hexdump of the device/file indicates that the third block of 512 bytes (starting at offset 0x200) is different from the other three (starting at 0, 0x100 and 0x300). Meanwhile, in your code snippet, I'm having trouble tracking your intent with the four "sysseek/sysread" pairs -- looks like the first two amount to reading the same block twice (?? -- was that a copy/paste error?). And as for the third and fourth pairs, you didn't mention how big the file actually is, and in any case, seeking from the end of the file seems like an unnecessary complication (possibly a mistake). Since the first two reads (first two elements of the array) are in fact the exact same data (from the same position in the file), your initial "if" block is never entered. (And why did you say `if (!($SB[0] eq $SB[1]))` instead of the simpler `if ( $SB[0] ne $SB[1] )`?) So, what's the problem again? I don't think it's the "eq" (or "ne") comparison... I think it's a mistake in how you are reading the data from the file.	[reply] [d/l] [select]
Re^4: Test binary equality? by exodist (Monk) on Jun 21, 2007 at 03:50 UTC
sorry, yes I meant all 4, and the hexdump I pasted was after I zero's out the first 512 bytes to test and make sure it would detect that they were different and give me an error. The bug was that my first 2 seeks were to the same position. I seek to the end of the file because I do not know how big the file will be, I am dealing with block devices, not real files. All I know is the first 2 and last 2 512 bytes are supposed to be identical. I know that there are 2 seeks in there that are not important since they seek to where it should be anyway, but I am not necessarily keeping the code as is and may put other stuff in between them, so I put the seeks in for now so I do not forget later.	[reply]