> Ed Chester wrote:
>
>>>Hi all.
>>>I have a problemette with the following scripting issue.
>>>Its not primarily a technical problem... I quickly wrote a
>>>script that
>>>did exactly what I want, if possibly inelegantly. The problem
>>>I have is that a colleague wrote, (get this) a _visual basic_
>>><shudder>, program that does the same thing about 100 times
>>>faster. I am devastated.
>>>The truly sad thing is that I'm too focussed on the first
>>>solution to work out a faster way of doing it.
>>>
>>>Here's the problem:
>>>Got a large file (>1Mb) containing binary data.
>>>Bytes are in the correct order.
>>>Each byte is in low-endian order (lsb first).
>>>Want write an output file with bytes in the same order, but with
>>> each byte big-endianed.
>>>
It seems to me that the fastest way to solve this
problem would be with a transform, i.e. tr or y, operator.
That way all the computatiomal work could be done by
perl at compile time. It might be interesting to write
a perl script to generate the two strings used by the tr
operator
>>>Sounds simple. So I broke out my old friend Bit::Vector, and
>>>here's what I did (surrounding stuffs snipped):
>>>
>>>while (read LL, my $b, 1) {
>>> my $h = unpack "H*", $b;
>>> my $b_h = Bit::Vector -> new_Hex(8,$h) -> to_Bin;
>>> my $r = reverse($b_h);
>>> print OF pack "H*", Bit::Vector -> new_Bin(8,$r) -> to_Hex;
>>> }
>>>
>>>LL is my filehandle, $b is current byte, OF is output filehandle,
>>>$r the byte in the order I want it for output.
>>>
>>>Now I realise that the cause of my woe is that I'm using
>>>bit::vector to do something that its really overqualified
>>>for, and also that
>>>I convert to and from binary and hex unecessarily. I can probably
>>>skip packing and unpacking, probably not use Bit::Vector, and
>>>have a much faster solution - but nothing I've tried has
>>>worked. I also
>>>failed spectacularly to use Bit::Vector's Reverse method.
>>>Thinking it was clever, I also tried doing things with
>>>bitwise & and | to
>>>map bytes into the other endian form. No joy.
>>>
>>>SO - given I know somebody out there has done this before,
>>>and that you all are laughing at the type changes going on in
>>>the code above, can somebody take me out of my misery and
>>>suggest improvements so I don't have to spend my weekend
>>>feeling like I've allowed VB to do a
>>>better job than Perl?
>
> Try this:
>
> use strict;
>
> # create a byte conversion hash - one time so cheap
>
> for (0 .. 255) {
> my $b = 0;
> for (my $ii = 0; $ii < 8; $ii++) {
> if ($_ & (1 << $ii)) {
> $b |= (0x80 >> $ii);
> }
> }
> $hash{$_} = $b;
> }
>
> # open files
>
> open LL ....
> binmode LL;
> open FF ....
> binmode FF;
>
> # convert each byte using hash
>
> while (read LL, my $b, 1) {
> print OF $hash{$_};
> }
>
> close LL;
> close FF;
>
>
> --
> ,-/- __ _ _ $Bill Luebkert Mailto:[EMAIL PROTECTED]
> (_/ / ) // // DBE Collectibles Mailto:[EMAIL PROTECTED]
> / ) /--< o // // Castle of Medieval Myth & Magic
> http://www.todbe.com/
> -/-' /___/_<_</_</_ http://dbecoll.tripod.com/ (My Perl/Lakers stuff)
>
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