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Re: Locating sequence of bytes within binary file [message #71451 is a reply to message #71379]

Fri, 18 June 2010 09:47

Axel Martínez
Messages: 22
Registered: June 2010

Junior Member

Wow, I had read in Coyote's website that JD Smith always finds amazing
solutions ;), but this is over any expectation!! I am simply amazed.
Not only I see all possible solutions for my problem and their
drawbacks, but I also learn a lot!

I spent some time to understand the methods, managed now...

> As usual, we can (over-)use IDL's array strengths to brute-force this
> using REBIN and dimensional TOTAL:

The problem of this solution might be the size of the variable quill
for a large "needle" (not my case). And also the speed, as you
acknowledge...

> That motivates another deeply unsatisfying, but resoundingly faster
> (20-50x) option: simply replace all 0b's with 1b's in both input byte
> array and search array, and just double-check for spurious matches as
> you go:

This is good, but it just uses double the amount of memory to preserve
the original and the modified array. Works for me, but could be bad
for others. And, honestly, it is really not so elegant.

> We might also lobby ITT to let STRPOS and its sort accept byte arrays
> (since frankly there is very little difference between them
> internally).

This would be by far the best solution. I believe a VIP like you have
more options to lobby ITT than I do :) Maybe creating a "BYTPOS" or
actually "ANYDATAFORMAT_POS" function would be good. A similar problem
might arise looking for a sequence of integers instead of bytes...

My problem is small, and solved by any of the solutions which were
proposed. But it would be good to have a fast and memory-efficient
option available for future IDL-users :) Next time then I do not need
to be ashamed of saying that IDL does virtually everything with
arrays.

Thanks so much!!!

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[Message index]

		Locating sequence of bytes within binary file By: medd on Tue, 15 June 2010 04:30
		Re: Locating sequence of bytes within binary file By: JDS on Thu, 17 June 2010 10:48
		Re: Locating sequence of bytes within binary file By: Axel Martínez on Fri, 18 June 2010 09:47
		Re: Locating sequence of bytes within binary file By: medd on Thu, 17 June 2010 01:03
		Re: Locating sequence of bytes within binary file By: penteado on Wed, 16 June 2010 10:46
		Re: Locating sequence of bytes within binary file By: David Fanning on Fri, 18 June 2010 15:21
		Re: Locating sequence of bytes within binary file By: kamal on Thu, 24 June 2010 01:42
		Re: Locating sequence of bytes within binary file By: JDS on Fri, 18 June 2010 15:12

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