Isn't the point of a LFSR that it cannot be decoded?

Besides which, for 20-bit numbers there are only 1e6 mappings, so it would be easier and faster to set up a pair of lookup tables (One time pad): 

use List::Util qw[ shuffle ];;

@n = 1 .. 2**20;;
@encoded = shuffle @n;;

@encode{ @n } = @encoded;;
@decode{ @encoded } = @n;;

print total_size $_ for \( %encode, %decode );;
44036216
44068014

[download]

One-time pads are the safest encryption mechanism (used properly!), and < 100MB very easy to generate.

Of course, using them properly means never re-using them which can present an off-line storage problem, but an entire pad can be reduced to ~2.5MB. How many would you need?

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
RIP PCW

In reply to Re: LFSRs & binary encode / decode functions by BrowserUk
in thread LFSRs & binary encode / decode functions by zardoz99

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