in reply to Re^7: [OT] The interesting problem of comparing bit-strings.
in thread [OT] The interesting problem of comparing bit-strings.

The idea is that for long needles, you can discard their borders (the unaligned bits), search for the middle string using some efficient algorithm and only when it matches, check the borders

I get that. But even then, there is not "the middle bit", but rather 'eight middle bits' (and upto 7 different unaligned bits, at either end):

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Note that the "aligned middle bits" are different every bit offset, cycling every 8 bits.

Of course the same problem occurs with 64-bit units, but rotating the 64-bit units using 64, single instruction, 128-bit shiftlefts, is far more efficient than doing 64 x 8 x 16-bit shifts to achieve the same thing.


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