Michael C. Toren on 12 Sep 2004 00:34:03 -0000

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Re: [PLUG] corrupt jpeg

On Sat, Sep 11, 2004 at 04:40:36PM -0400, Jeff Abrahamson wrote:
> But part of the context you trimmed showed that the byte change was from
> 0xF5 to 0x95.  (I didn't verify but took the original poster's word for
> it.)  That means a high bit was lost, but other high bits were not lost.
> The file was long enough that a single bit error is not so easily
> explained.  (Recall that only *one* bit in the whole file changed.)

A change from 0xF5 to 0x95 involves changing two bits in the high nibble;
0xF is 0b1111, while 0x9 is 0b1001.


perl -e'$u="\4\5\6";sub H{8*($_[1]%79)+($_[0]%8)}sub G{vec$u,H(@_),1}sub S{vec
($n,H(@_),1)=$_[2]}$_=q^{P`clear`;for$iX){PG($iY)?"O":" "forX8);P"\n"}for$iX){
forX8){$c=scalar grep{G@$_}[$i-1Y-1Z-1YZ-1Y+1ZY-1ZY+1Z+1Y-1Z+1YZ+1Y+1];S$iY,G(
/,\$_/xg;s/X/(0..7/g;s/P/print+/g;eval' #     Michael C. Toren <mct@toren.net>

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