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we can shift the range to 0
and subtract the beginning of the range from the public key
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This "shift" was already discussed here. And moreover, Jean_Luc made the shift in his program.
So if we input the range [a..b], the program actually shifts it to 0 and making the search within the range [0... (a-b)]
I also read all read all the DPs from binary file and can confirm this: all the tames distances are within the range [0...(a-b)] and all the wilds are within the range [0...(a-b)/2] - for wilds also the sign is used.
But you are right, Etar, that the "tame" DPs from previous keys could be used for subsequent, however their concentration will be very high on the left side of the range. Tames are distributed within the whole range, however if you use these tames for 1bit more key, they are all be only within the first half of the range, if for 2bit more key, all the tames will be on the first 25% of the range, etc...
But yes, the working files could be used for higher bits keys. However you should use the same DP size.